1991 BMW 5 SERIES Speed

reading should be between 400 and 500 mA.
Adjust the valve if the current reading is not as
specified. Note: The idle air stabiliser current
will fluctuate between 400 and 1100 mA if the
engine is too cold, if the coolant temperature
sensor is faulty, if there is an engine vacuum
leak, or if electrical accessories are on.
25If there is no current reading, have the idle
speed control unit (under the facia) checked
by a BMW dealer or other specialist.
26On three-wire valves, check for voltage at
the electrical connector. With the ignition on,
there should be battery voltage present at the
centre terminal (see illustration). There
should be about 10 volts between the centre
terminal and each of the outer terminals.
27If there is no voltage reading, have the idle
speed control unit (early models) or the ECU
(later models) checked by a dealer service
department or other specialist.
Adjustment (early models only)
28With the ignition switched off, connect a
tachometer in accordance with the equipment
manufacturer’s instructions.
29Make sure the ignition timing is correct
(see Chapter 5).
30Connect an ammeter to the valve as
described in paragraph 13.
31With the engine running, the current draw
should be 450 to 470 mA at 700 to 750 rpm.
32If the control current is not correct, turn
the adjusting screw until it is within the
specified range. Note: Turn the idle air bypass
screw clockwise to increase the current, or
anti-clockwise to decrease the current.
Renewal
33Remove the electrical connector and the
bracket from the idle air stabiliser valve.
Remove the valve, disconnecting the hoses.
34Refitting is the reverse of removal.
22 Exhaust system servicing-
general information
Warning: Inspect or repair
exhaust system components only
when the system is completely
cool. When working under the
vehicle, make sure it is securely
supported.
Silencer and pipes
1The exhaust system consists of the exhaust
manifold, catalytic converter, silencers, and all
connecting pipes, brackets, mountings (see
illustration)and clamps. The exhaust system
is attached to the body with brackets and
rubber mountings. If any of the parts are
improperly fitted, excessive noise and
vibration may be transmitted to the body.
2Inspect the exhaust system regularly. Look
for any damaged or bent parts, open seams,
holes, loose connections, excessive
corrosion, or other defects which could allow
exhaust fumes to enter the vehicle. Generally,
deteriorated exhaust system components
cannot be satisfactorily repaired; they should
be renewed.3If the exhaust system components are
extremely corroded or rusted together, it may
be necessary to cut off the old components
with a hacksaw. Be sure to wear safety
goggles to protect your eyes from metal
chips, and wear work gloves to protect your
hands.
4Here are some simple guidelines to follow
when repairing the exhaust system:
a) Work from the back to the front of the
vehicle when removing exhaust system
components.
b) Apply penetrating oil to the exhaust
system nuts and bolts to make them
easier to remove.
c) Use new gaskets, mountings and clamps
when fitting exhaust system components.
d) Apply anti-seize compound to the threads
of all exhaust system nuts and bolts
during reassembly.
e) Be sure to allow sufficient clearance
between newly-fitted parts and all points
on the underbody, to avoid overheating
the floorpan, and possibly damaging the
interior carpet and insulation. Pay
particularly close attention to the catalytic
converters and heat shields. Also, make
sure that the exhaust will not come into
contact with suspension parts, etc.
Catalytic converter
5Although the catalytic converter is an
emissions-related component, it is discussed
here because, physically, it’s an integral part
of the exhaust system. Always check the
converter whenever you raise the vehicle to
inspect or service the exhaust system.
6Raise and support the vehicle.
7Inspect the catalytic converter for cracks or
damage.
8Check the converter connections for
tightness.
9Check the insulation covers welded onto the
catalytic converter for damage or a loose fit.
Caution: If an insulation cover is
dented so that it touches the
converter housing inside,
excessive heat may be
transferred to the floor.
10Start the engine and run it at idle speed.
Check all converter connections for exhaust
gas leakage.
4•20 Fuel and exhaust systems
22.1 A typical exhaust system rubber
mounting21.26 Check for battery voltage on the
centre terminal

Fuel injection system - fault finding
L-Jetronic fuel injection system
Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch faulty Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump inoperative Check fuel pump fuse and fuel pump relay (see Sections 3 and 4)
Airflow meter flap (door) binding or stuck
in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3). Test fuel pressure regulator (Section 18)
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating continuously Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pump(s). Renew if necessary (see Section 3)
Insufficient residual fuel pressure Test residual fuel pressure. Renew fuel pump or fuel accumulator as necessary
(see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as required (see Chapter 4)
Coolant temperature sensor faulty or
wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (warm weather) Check fuel pressure (see Section 3)
EVAP system faulty (where applicable) Check EVAP system (see Chapter 6, Section 6)
Incorrect ignition timing Check ignition timing (see Chapter 5). Check vacuum advance system
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged or faulty Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Vacuum advance system faulty Check vacuum advance system and electronic vacuum advance relay
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Motronic fuel injection system
Note:With this system, when faults occur, the ECU stores a fault code in its memory. These codes can only be read by a BMW dealer, as
specialised equipment is required. It may save time to have at least the initial fault diagnosis carried out by a dealer.
Lack of power
Probable cause Corrective action
Coolant temperature sensor faulty, Test coolant temperature sensor and wiring. Repair wiring or renew sensor if
or wire to sensor broken faulty (see Chapter 6)
Fuel pressure incorrect Check fuel pressure from main pump and transfer pump, as applicable (see Section 3)
Throttle plate not opening fully Check accelerator cable adjustment to make sure throttle is opening fully. Adjust cable if
necessary (see Section 9)
Fuel and exhaust systems 4•21
4

Engine difficult to start, or fails to start (when cold)
Probable cause Corrective action
Cold start injector or thermotime switch
faulty (early Motronic system only) Test cold start injector and thermotime switch. Renew faulty components (see Section 19)
Fuel pump not running Check fuel pump fuse and fuel pump relay (see Sections 2 and 3)
Airflow meter flap (door) binding, or
stuck in open position Inspect the airflow meter for damage (see Section 16)
Fuel pressure incorrect Test system pressure (see Section 3)
Intake air leaks Inspect all vacuum lines, air ducts and oil filler and dipstick seals
Fuel injectors clogged or not operating Check fuel injectors (see Section 20) and wiring harness
Coolant temperature sensor faulty or Test coolant temperature sensor (see Chapter 6, Section 4)
wiring problem
TPS (throttle position sensor) incorrectly adjusted Check TPS adjustment (see Chapter 6, Section 4)
Dirt or other contaminants in fuel Check the fuel and drain the tank if necessary
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Crankshaft position signal missing Faulty position sensor or flywheel, or reference pin missing (see Chapter 5)
Engine difficult to start, or fails to start (when warm)
Probable cause Corrective action
Cold start injector leaking or operating
continuously (early Motronic system only) Test cold start injector and thermotime switch (see Section 19)
Fuel pressure incorrect Test fuel pressure (see Section 3)
Insufficient residual fuel pressure Test fuel system hold pressure (see Section 3)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks. Correct leaks as necessary
Coolant temperature sensor faulty
or wiring problem Test coolant temperature sensor (see Chapter 6, Section 4)
Vapour lock (in warm weather) Check fuel pressure (see Section 3)
EVAP system faulty Check EVAP system (see Chapter 6, Section 6)
Faulty ECU Have the ECU tested at a dealer service department or other specialist
Idle speed control system faulty Test the idle air stabiliser valve (see Section 21)
Oxygen sensor faulty (where applicable) Check the oxygen sensor (see Chapter 6, Section 4)
Engine misses and hesitates under load
Probable cause Corrective action
Fuel injector clogged Test fuel injectors. Check for clogged injector lines. Renew faulty injectors (see Section 20)
Fuel pressure incorrect Test fuel system pressure (see Section 3). Test fuel pressure regulator (see Section 18)
Fuel leak(s) Inspect fuel lines and fuel injectors for leaks (see Chapter 4)
Engine maintenance Tune-up engine (see Chapter 1). Check the distributor cap, rotor, HT leads and spark
plugs, and renew any faulty components
Airflow meter flap (door) binding, or Inspect the airflow meter for damage (see Section 16)
stuck in open position
Intake air leaks Inspect all vacuum lines, air ducts, and oil filler and dipstick seals
Throttle position sensor (TPS) incorrectly adjusted Check TPS adjustment (see Chapter 6)
Engine idles too fast
Probable cause Corrective action
Accelerator pedal, cable or throttle valve binding Check for worn or broken components, kinked cable, or other damage. Renew faulty
components
Air leaking past throttle valve Inspect throttle valve, and adjust or renew as required
Engine has erratic idle speed
Probable cause Corrective action
Idle air stabiliser valve faulty Check the idle air stabiliser valve (see Section 21)
No power to the idle air stabiliser valve Check the idle air stabiliser relay and wiring circuit (see Chapter 12)
Idle speed control unit faulty Have the idle speed control unit checked by a dealer
Poor fuel economy
Probable cause Corrective action
Cold start injector leaking
(early Motronic system only) Test and, if necessary, renew cold start injector (see Section 19)
Oxygen sensor faulty (where applicable) Test the oxygen sensor (see Chapter 6, Section 4))
Sticking handbrake/binding brakes Check the handbrake/braking system (see Chapter 9)
Tyre pressures low Check tyre pressures (Chapter 1)
4•22 Fuel and exhaust systems

5 Ignition system- general
information and precautions
The ignition system includes the ignition
switch, the battery, the distributor, the primary
(low-voltage/low-tension or LT) and
secondary (high-voltage/high-tension or HT)
wiring circuits, the spark plugs and the spark
plug leads. Models fitted with a carburettor or
L-Jetronic fuel injection are equipped with a
Transistorised Coil Ignition (TCI) system.
Models fitted with the Motronic fuel injection
system have the ignition system incorporated
within the Motronic system (Digital Motor
Electronics or DME).
Transistorised Coil Ignition (TCI)
system
This system is has four major components;
the impulse generator, the ignition control
unit, the coil, and the spark plugs. The
impulse generator provides a timing signal for
the ignition system. Equivalent to cam-
actuated breaker points in a standard
distributor, the impulse generator creates an
A/C voltage signal every time the trigger
wheel tabs pass the impulse generator tabs.
When the ignition control unit (capacitive
discharge unit) receives the voltage signal, it
triggers a spark discharge from the coil by
interrupting the primary coil circuit. The
ignition dwell (coil charging time) is adjusted
by the ignition control unit for the most
intense spark. Note: The air gap (distance
between the impulse generator and trigger
wheel tabs) can be adjusted (see Section 11).
Ignition timing is mechanically adjusted
(see Section 7). A centrifugal advance unit
that consists of spring-loaded rotating
weights advances ignition timing as engine
speed increases. The vacuum advance
adjusts ignition timing to compensate for
changes in engine load.
Motronic ignition system
This system, also known as Digital Motor
Electronics (DME), incorporates all ignition
and fuel injection functions into one central
control unit or ECU (computer). The ignition
timing is based on inputs the ECU receives for
engine load, engine speed, coolant
temperature and intake air temperature. The
only function the distributor performs is the
distribution of the high voltage signal to the
individual spark plugs. The distributor is
attached directly to the cylinder head. There is
no mechanical spark advance system used on
these systems.
Ignition timing is electronically-controlled,
and is not adjustable on Motronic systems.
During starting, a crankshaft position sensor
(reference sensor) relays the crankshaft
position to the ECU, and an initial baseline
ignition point is determined. Once the engineis running, the ignition timing is continually
changing, based on the various input signals
to the ECU. Engine speed is signalled by a
speed sensor. Early Motronic systems have
the position reference sensor and the speed
sensor mounted on the bellhousing over the
flywheel on the left-hand side. Later Motronic
systems have a single sensor (pulse sensor)
mounted over the crankshaft pulley. This
sensor functions as a speed sensor as well as
a position reference sensor. Refer to Sec-
tion 12 for checking and renewing the ignition
sensors. Note: Some models are equipped
with a TDC sensor mounted on the front of the
engine. This sensor is strictly for the BMW
service test unit, and it is not part of the
Motronic ignition system.
Precautions
Certain precautions must be observed
when working on a transistorised ignition
system.
a) Do not disconnect the battery cables
when the engine is running
b) Make sure the ignition control unit (TCI
ignition system) is always well earthed
(see Section 10).
c) Keep water away from the distributor and
HT leads.
d) If a tachometer is to be connected to the
engine, always connect the tachometer
positive (+) lead to the ignition coil
negative terminal (-) and never to the
distributor.
e) Do not allow the coil terminals to be
earthed, as the impulse generator or coil
could be damaged.
f) Do not leave the ignition switch on for
more than ten minutes with the engine
off, or if the engine will not start.
6 Ignition system- check
2
Warning: Because of the high
voltage generated by the ignition
system, extreme care should be
taken whenever an operation is
performed involving ignition components.
This not only includes the impulse
generator (electronic ignition), coil,
distributor and spark plug HT leads, but
related components such as spark plug
connectors, tachometer and other test
equipment.
1If the engine turns over but will not start,
disconnect the spark plug HT lead from any
spark plug, and attach it to a calibrated spark
tester (available at most car accessory
shops).
Note:There are two different types of spark
testers. Be sure to specify electronic
(breakerless) ignition. Connect the clip on thetester to an earth point such as a metal
bracket (see illustration).
2If you are unable to obtain a calibrated
spark tester, remove the spark plug HT lead
from one of the spark plugs. Using an
insulated tool, hold the lead about a quarter-
inch from the engine block - make sure the
gap is not more than a quarter-inch, or
damage may be caused to the electronic
components.
3Crank the engine, and observe the tip of the
tester or spark plug HT lead to see if a spark
occurs. If bright-blue, well-defined sparks
occur, sufficient voltage is reaching the plugs
to fire the engine. However, the plugs
themselves may be fouled, so remove and
check them as described in Chapter 1.
4If there’s no spark, check another HT lead
in the same manner. A few sparks followed by
no spark is the same condition as no spark at
all.
5If no spark occurs, remove the distributor
cap, and check the cap and rotor as
described in Chapter 1. If moisture is present,
use a water-dispersant aerosol (or something
similar) to dry out the cap and rotor, then refit
the cap and repeat the spark test.
6If there’s still no spark, disconnect the coil
HT lead from the distributor cap, and
test this lead as described for the spark plug
leads.
7If no spark occurs, check the primary wire
connections at the coil to make sure they’re
clean and tight. Make any necessary repairs,
then repeat the check.
8If sparks do occur from the coil HT lead, the
distributor cap, rotor, plug HT lead(s) or spark
plug(s) may be defective. If there’s still no
spark, the coil-to-cap HT lead may be
defective. If a substitute lead doesn’t make
any difference, check the ignition coil (see
Section 9). Note:Refer to Sections 10 and 11
for more test procedures on the distributors
fitted with the TCI ignition system.
Engine electrical systems 5•3
6.1 To use a spark tester, simply
disconnect a spark plug HT lead, clip the
tester to a convenient earth (like a valve
cover bolt or nut) and operate the starter –
if there is enough power to fire the plug,
sparks will be visible between the
electrode tip and the tester body
5

7 Ignition timing (TCI system)-
check and adjustment
4
Warning: Keep hands, equipment
and wires well clear of the
viscous cooling fan during
adjustment of the ignition timing.
Note:This Section describes the procedure
for checking and adjusting the ignition timing
on engines fitted with the TCI system. On
engines fitted with the Motronic engine
management system, the ignition timing is
controlled by the electronic control unit, and
no adjustment is possible. The timing can be
checked using the following procedure, but no
ignition timing values were available at the
time of writing. If the timing is thought to be
incorrect, refer to a BMW dealer.
1Some special tools are required for this
procedure (see illustration). The engine must
be at normal operating temperature, and the
air conditioning (where fitted) must be
switched off. Make sure the idle speed is
correct.
2Apply the handbrake, and chock the wheels
to prevent movement of the vehicle. The
transmission must be in neutral (manual) or
Park (automatic).
3The timing marks are located on the engine
flywheel (viewed through the timing checkhole in the bellhousing) and/or on the vibration
damper on the front of the engine.
4Where applicable, disconnect the vacuum
hose from the distributor vacuum advance
unit.
5Connect a tachometer and timing light
according to the equipment manufacturer’s
instructions (an inductive pick-up timing light
is preferred). Generally, the power leads for
the timing light are attached to the battery
terminals, and the pick-up lead is attached to
the No 1 spark plug HT lead. The No 1 spark
plug is the one at the front of the engine.
Caution: If an inductive pick-up
timing light isn’t available, don’t
puncture the spark plug HT lead
to attach the timing light pick-up
lead. Instead, use an adapter between the
spark plug and HT lead. If the insulation on
the HT lead is damaged, the secondary
voltage will jump to earth at the damaged
point, and the engine will misfire.
Note:On some models, a TDC transmitter is
fitted for checking the ignition system.
However, a special BMW tester must be
connected to the diagnostic socket to use it,
so unless the special tester is available, a
conventional timing light should be used. The
ignition timing mark may be on the vibration
damper, but if not, normally the TDC mark will
be. If the timing light is of the adjustable delay
type, then the ignition timing may be
determined by zeroing the adjustment, then
turning the adjustment until the TDC marks are
aligned, and then reading off the amount of
advance from the timing light. If a standard
timing light is being used, make a mark on the
vibration damper in accordance with the
specified advance, using the following formula
to calculate the distance from the TDC mark
to the timing mark:
Distance = 2Pr x advance
360
where P = 3.142
r = radius of vibration damper
advance = specified advance
BTDC in degrees
6With the ignition off, loosen the distributor
clamp nut just enough to allow the distributor
to pivot without any slipping.7Make sure the timing light wires are routed
away from the drivebelts and fan, then start
the engine.
8Raise the engine rpm to the specified
speed, and then point the flashing timing light
at the timing marks - be very careful of moving
engine components.
9The mark on the flywheel or vibration
damper will appear stationary. If it’s aligned
with the specified point on the bellhousing or
engine front cover, the ignition timing is
correct (see illustrations).
10If the marks aren’t aligned, adjustment is
required. Turn the distributor very slowly until
the marks are aligned, taking care not to
touch the HT leads.
11Tighten the nut on the distributor clamp,
and recheck the timing.
12Switch off the engine, and remove the
timing light and tachometer. Reconnect the
vacuum hose where applicable.
8 Distributor-
removal and refitting
4
TCI system
Removal
1After carefully marking them for position,
remove the coil HT lead and spark plug HT
leads from the distributor cap (see Chapter 1).
2Remove No 1 spark plug (the one nearest
you when you are standing in front of the
engine).
3Manually rotate the engine to Top Dead
Centre (TDC) on the compression stroke for
No 1 piston (see Chapter 2A)
4Carefully mark the vacuum hoses, if more
than one is present on your distributor.
5Disconnect the vacuum hose(s).
6Disconnect the primary circuit wires from
the distributor.
7Mark the relationship of the rotor tip to the
distributor housing (see illustration). Also
mark the relationship of the distributor
housing to the engine.
5•4 Engine electrical systems
7.1 Tools for checking and adjusting the
ignition timing
1Vacuum plugs- Vacuum hoses will, in
most cases, have to be disconnected and
plugged. Moulded plugs in various shapes
and sizes can be used for this, if wished
2Inductive pick-up timing light- Flashes a
bright, concentrated beam of light when
No 1 spark plug fires. Connect the leads
according to the instructions supplied with
the light
3Distributor spanner - On some models,
the hold-down bolt for the distributor is
difficult to reach and turn with conventional
spanners or sockets. A special spanner like
this must be used
7.9a Flywheel “OT” timing mark 7.9b Flywheel “OZ” timing mark

and down - you should feel a slight drag on
the feeler gauge as it is moved if the gap is
correct. The gap must be as given in this
Chapter’s Specifications.
3To adjust the gap, it is necessary to remove
the impulse generator and the baseplate
assembly from the distributor (see illus-
tration 10.1).
4Follow paragraphs 17 to 24 in Section 10
and loosen the screws that retain the impulse
generator to the baseplate assembly.
5Carefully insert the feeler gauge and tighten
the screws.
6Refit the assembly back into the distributor
and recheck the adjustment.12 Ignition sensors (Motronic
system)- check and renewal
2
Note:Some models are equipped with a TDC
sensor mounted on the front of the engine.
This sensor is strictly for the BMW service test
unit, and is not part of the Motronic ignition
system.
Speed and position sensors
Check
1Locate the two electrical connectors for the
sensors (see illustrations). The grey
connector is for the position sensor, and the
white connector is for the speed sensor.
2Using an ohmmeter, check the resistance
between terminal 1 (yellow wire) and terminal
2 (black wire) on the sensor side of each
connector. The resistance should be 860 to
1,060 ohms.
3Also check the resistance between terminal
3 and either terminal 1 or terminal 2. The
resistance should be approximately 100 000
ohms.
4If the reading(s) are incorrect, renew the
sensor(s).
Renewal
5Remove the sensor mounting screw(s),using an Allen key where necessary, and pull
the sensor(s) from the sockets. Disconnect
the wiring from one sensor at a time - be sure
the connectors are not interchanged when
fitting new sensors. The bellhousing is marked
with a B for the position sensor (grey
connector) and D for the speed sensor (black
connector) (see illustration). Note: It is a
good idea to check the condition of the raised
pin on the flywheel while the sensors are out
of the sockets. Turn the engine by hand as
necessary to bring the pin into view.
6Tighten the sensor mounting screw(s)
securely, but be careful not to overtighten.
Pulse sensor (later models)
Check
7Locate the two electrical connectors for the
sensor (see illustrations). Disconnect the
electrical connector from the front.
8Using an ohmmeter, check resistance
between terminal 1 (yellow wire) and terminal
2 (black wire) on the sensor side of each
connector (see illustration). The resistance
should be 500 to 600 ohms.
9If the reading is incorrect, renew the sensor.
Renewal
10Remove the pulse sensor mounting bolt
using a 5 mm hex spanner (see illustration).
5•8 Engine electrical systems
12.10 The pulse sensor itself (arrowed) is
located on the timing belt cover, to one
side of the pulley (later models)12.8 The resistance of the pulse sensor
should be 500 to 600 ohms (later models)12.7b On later 5-Series models, the pulse
sensor connector (arrowed) is located next
to the valve cover
12.7a On later 3-Series models, the pulse
sensor connector (arrowed) is located next
to the 20-pin diagnostic connector
12.5 Location of the position sensor (B) and
speed sensor (D) on the bellhousing on all
Motronic systems – do not interchange the
sensors, or the engine will not start12.1b Location of the position sensor
(grey connector) (A) and the speed sensor
(black connector) (B) on Motronic systems
(later models)12.1a Location of the position sensor (grey
connector) (A) and the speed sensor (black
connector) (B) on Motronic systems (early
models)

when the transmission selector lever is in Park
or Neutral.
Always detach the battery negative cable
before working on the starting system.
19 Starter motor-
in-vehicle check
2
Note:Before diagnosing starter problems,
make sure the battery is fully charged.
1If the starter motor does not turn at all when
the switch is operated, make sure that the
gear lever is in Neutral or Park (automatic
transmission) or, where applicable, that the
clutch pedal is depressed (manual
transmission).
2Make sure that the battery is charged, and
that all cables, both at the battery and starter
solenoid terminals, are clean and secure.
3If the starter motor spins but the engine is
not cranking, the overrun clutch in the starter
motor is slipping, and the starter motor must
be renewed.
4If, when the switch is actuated, the starter
motor does not operate at all but the solenoid
clicks, then the problem lies either in the
battery, the main solenoid contacts, or the
starter motor itself (or the engine is seized).
5If the solenoid plunger cannot be heard
when the switch is actuated, the battery is
faulty, the switch is defective, the fusible link
is burned-out (the circuit is open), or the
solenoid itself is defective.
6To check the solenoid, connect a jumper
lead between the battery (+) and the ignition
switch wire terminal (the small terminal) on the
solenoid. If the starter motor now operates,
the solenoid is OK and the problem is in the
ignition switch, starter inhibitor switch
(automatic transmission models), clutch
switch (some manual transmission models), or
the wiring.
7If the starter motor still does not operate,
remove the starter/solenoid assembly for
dismantling, testing and repair.
8If the starter motor cranks the engine at an
abnormally-slow speed, first make sure that
the battery is charged, and that all terminal
connections are tight. If the engine is partially-
seized, or has the wrong viscosity oil in it, it
will crank slowly.
9Run the engine until normal operating
temperature is reached, then disconnect the
coil HT lead from the distributor cap and earth
it on the engine.
10Connect a voltmeter positive lead to the
battery positive post, and connect the
negative lead to the negative post.11Crank the engine, and take the voltmeter
readings as soon as a steady figure is
indicated. Do not allow the starter motor to
turn for more than 10 seconds at a time. A
reading of 9 volts or more, with the starter
motor turning at normal cranking speed, is
normal. If the reading is 9 volts or more but
the cranking speed is slow, the solenoid
contacts are burned, there is a bad
connection, or the starter motor itself is faulty.
If the reading is less than 9 volts and the
cranking speed is slow, the starter motor is
faulty or the battery is responsible (defective
or discharged).
20 Starter motor-
removal and refitting
1
Note:If the starter motor is defective, it should
be renewed, or taken to an auto electrical
specialist for repair. Overhaul of the starter
motor is unlikely to be a practical proposition
for the home mechanic, even if spare parts are
available. However, the solenoid can be
renewed separately (see Section 21).
Removal
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
1Detach the battery negative cable.
2Raise the vehicle and support it securely on
axle stands.
3Clearly label the wires from the terminals onthe starter motor and solenoid, then
disconnect them. Note: On some models, it
may be necessary to remove the air cleaner
(see Chapter 4), coolant expansion tank (see
Chapter 3) and the heater hoses to gain
access to the top of the starter. Carefully label
any hoses or components that need to be
removed from the engine compartment, to
avoid confusion when reassembling.
4Unscrew the mounting bolts and detach the
starter (see illustrations).
Refitting
5Refitting is the reverse of removal.
21 Starter solenoid-
removal and refitting
1
Removal
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
1Disconnect the battery negative cable.
2Remove the starter motor (see Section 20).
3Disconnect the cable from the solenoid to
the starter motor terminal.
4Remove the screws which secure the
solenoid to the starter motor.
5Detach the solenoid from the starter body.
6Remove the plunger and plunger spring.
Refitting
7Refitting is the reverse of removal.
5•12 Engine electrical systems
20.4b Withdrawing the starter motor from
the M40 engine20.4a Working under the vehicle, remove
the starter lower mounting bolt and nut
(arrowed)

Check
12Warm up the engine, and let it run at idle.
Disconnect the oxygen sensor electrical
connector, and connect the positive probe of
a voltmeter to the oxygen sensor output
connector terminal (refer to the following
table) and the negative probe to earth (see
illustrations).
Note:Most oxygen sensor electrical
connectors are located at the rear of the
engine, near the bulkhead. Look for a large
rubber boot attached to a thick wire harness.
On early 535i models, the connector for the
oxygen sensor heater circuit is under the
vehicle. Look for a small protective cover.
These models should have the updated
oxygen sensor fitted, to make access similar
to other models. Consult your dealer service
department for additional information.
13Increase and then decrease the engine
speed, and monitor the voltage.
14When the speed is increased, the voltage
should increase to 0.5 to 1.0 volts. When the
speed is decreased, the voltage should fall to
about 0 to 0.4 volts.
15Also where applicable, inspect the oxygen
sensor heater (models with multi-wire
sensors). With the ignition on, disconnect the
oxygen sensor electrical connector, and
connect a voltmeter across the terminals
designated in the chart (see below). There
should be battery voltage (approximately
12 volts).
16If the reading is not correct, check the
oxygen sensor heater relay (see Chapter 12).
If the information is not available, check the
owner’s handbook for the exact location of
the oxygen sensor heater relay. The relay
should receive battery voltage.
17If the oxygen sensor fails any of these
tests, renew it.
Renewal
Note: Because it is fitted in the exhaust
manifold, converter or pipe, which contracts
when cool, the oxygen sensor may be very
difficult to loosen when the engine is cold.
Rather than risk damage to the sensor(assuming you are planning to re-use it in
another manifold or pipe), start and run the
engine for a minute or two, then switch it off.
Be careful not to burn yourself during the
following procedure.
18Disconnect the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
19Raise and support the vehicle.
20Disconnect the electrical connector from
the sensor.
21Carefully unscrew the sensor.
Caution: Excessive force may
damage the threads.
22A high-temperature anti-seize compound
must be used on the threads of the sensor, to
facilitate future removal. The threads of new
sensors will already be coated with this
compound, but if an old sensor is removed
and refitted, recoat the threads.23Refit the sensor and tighten it securely.
24Reconnect the electrical connector of the
pigtail lead to the main engine wiring harness.
25Lower the vehicle, and reconnect the
battery.
Oxygen Sensor Heated power
sensor type output signal supply (12V)
Unheated
(single-wire) black wire (+) Not applicable
Heated terminal 1 (+) terminals
(three-wire) 3 (+) and 2 (-)
Heated terminal 2 (+) terminals
(four-wire) 4 (+) and 3 (-)
Throttle Position Sensor (TPS)
General description
26The Throttle Position Sensor (TPS) is
located on the end of the throttle shaft on the
throttle body. By monitoring the output
voltage from the TPS, the ECU can determine
fuel delivery based on throttle valve angle
(driver demand). In this system, the TPS acts
as a switch rather than a potentiometer. One
set of throttle valve switch contacts is closed
(continuity) only at idle. A second set of
contacts closes as the engine approaches
full-throttle. Both sets of contacts are open
(no continuity) between these positions. A
broken or loose TPS can cause intermittent
bursts of fuel from the injector and an
unstable idle, because the ECU thinks the
throttle is moving.
27All models (except for early 535i models
with automatic transmission) combine the idle
and full-throttle switch; a separate idle
position switch indicates the closed-throttle
position, while the TPS is used for the full-
throttle position. On 535i models with
automatic transmission, the TPS is connected
directly to the automatic transmission control
unit. With the throttle fully open, the
transmission control unit sends the full-
throttle signal to the Motronic control unit.
All models except early 535i with
automatic transmission
Check
28Remove the electrical connector from the
TPS, and connect an ohmmeter to terminals 2
and 18 (see illustrations). Open the throttle
Engine management and emission control systems 6•3
4.12b These oxygen sensor terminal
designations are for the harness side only.
Use the corresponding terminals on the
sensor side for the testing procedures
(there are three different four-wire oxygen
sensor connectors available - don’t get
them mixed up)4.12a The oxygen sensor, once it is
warmed up (320º C), puts out a very small
voltage signal. To verify it is working,
check for voltage with a digital voltmeter
(the voltage signals usually range from
0.1 to 1.0 volt)
4.28b First check for continuity between
terminals 2 and 18 with the throttle closed
(later Motronic system shown) . . .4.28a The TPS on L-Jetronic systems is
located under the intake manifold
(terminals arrowed)
6