1998 BMW 528i engine control system

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721-6
I Airbag System (SRS)
MRS
The MRS control module contains the electronic crash sensor
for frontal impact. Sensors mounted on the driver and
pas-
sengerfloor are used for side impacts. The MRS control mod-
ule
is located between the front seat under the center
console.
MRS airbag system
diagram
1. Driver's side airbag
2. Passenger's side airbag
3. Right side impact sensor
4. Seat occupancy sensor pad
5. Right side impact airbag
6. SBE control module (analog to
digital converter)
7. Passenger pyrotechnic seat belt
tensioner and seat belt
mi-
croswitch (Hall sensor MRS Ill)
8. MRS control module
9. Driver pyrotechnic seat belt ten-
sioner and seat belt microswitch
(Hall sensor MRS
Ill)
10. Left side impact airbag
11. Left side impact sensor

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Airbag System (SRS)~
MRS control module, replacing
- Disconnect negative (-) cable from battery and cover nega-
tive terminal with insulating material.
CAUTIOI\C
Prior to disconnecting the battery, read the battery discon-
nection cautionsgiven in001 General Warnings and
Cau-
tions.
- Remove center console between front seats. See 513 lnteri-
or Trim.
Remove module mounting nuts (arrows) and lift up control
module. Disconnect electrical harness connector.
Installation is reverse of removal.
Be sure that MRS control module ground cable is attached
to the module mounting stud.
Side-impact crash sensor, removing and
installing
- Make sure ignition key is OFF.
- Remove front seat. See 520 Seats.
Remove plastic door sill trim by lifting to release clips at one
end, then sliding off. Fold up carpet towards rear seat floor. If
necessary, remove floor level heater duct.

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OBD On-Board Diagnostics
I I
General ........................... OBD-1 Diaqnostic Trouble Codes (DTCs) . . OBD-9
On-Board Diagnostics (OBD I!) ..... OBD-I
Malfunction Indicator Light (MIL)
........ OBD-2
Scan tools and scan tool display.
........ OBD-3
Diagnostic monitors
.................. OED-4
Drive cycle
......................... OED-6
Readiness codes
.................... OBD-6
Diagnostic trouble codes
(DTCs) ........ OBD-7
-
Automatic transmission diagnostic
trouble codes
....................... OBD-9
Engine diagnostic trouble
codes: M52 engine.
................. OED-13
Engine diagnostic trouble
codes: M54 engine.
................. OBD-17
Engine diagnostic trouble
codes: M62 engine.
................. OBD-24
This chapter outlines the fundamentals and equipment
requirements of On-Board Diagnostics
I1 (OBD 11) standards
as they apply to BMW vehicles. Also covered here is a listing
of BMW and OBD
I1 diagnostic trouble codes (DTCs).
ON-BOARD DIAGNOSTICS (QBD !I)
OBD II standards were developed by the SAE (Society of
Automotive Engineers) and CARB (California Air Resources
Board).
OED I1 is the second generation of on-board self-
diagnostic equipment requirements. These standards were
originally mandated for California vehicles. Since
1996 they
have been applied
toall passengervehicles sold in the United
States.
On-board diagnostic capabilities are incorporated into the
hardware and soflwareof the enginecontrol module
(ECM) to
monitor virtually every component that can affect vehicle
emissions. The
OED I1 system works to ensure that
emissions remain as clean as possible over the life of the
vehicle.
Each emission-influencing component is checked by a
diagnostic routine (called a monitor) to verify that it is
functioning properly.
If a problem or malfunction is detected,
the
diagnostic executive built into the OBD I1 system
illuminates a malfunction indicator light (MIL) on the
instrument panel.
The OBD
I1 system also stores diagnostic trouble codes
(DTCs) about the detected malfunction in the ECM so that a
repair technician can accurately find and fix the problem.

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OED-2
On-Board Diagnostics
Specialized OED II scan tool equipment is needed to access
the fault memory and
OED I1 data.
The extra hardware needed to operate the OED
I1 system
consists mainly of the following:
* Additional oxygen sensors downstream of the catalytic
converters.
Fuel tank pressure sensor and device to pressurize
fuel
storage system.
Several engine and performance monitoring devices
Standardized 16-pin
OED II connector under the
dashboard.
Upgraded components for the federally required reliability
mandate.
Malfunction indicator light (MIL)
OED II software illuminates the malfunction indicator light
(MIL) when emission levels exceed 1.5 times Federal
standards.
4 For E34 cars covered by this manual, three different MIL
symbols were used, depending on year and model.
MIL illuminates under the following conditions:
Engine management system fault detected for
two
consecutive OED iI drive cycles. See Drive cycle in this
repair group.
- Catalyst damaging fault detected.
Component malfunction causes emissions to exceed 1.5
times OED
II standards.
Manufacturer-defined specifications exceeded. Implausible input signal.
Misfire
faults.
Leak in evaporative system,
Oxygen sensors observe no purge
flow from purge valve 1
evaporative system.
ECM fails to enter closed-loop operation within specified
time.
ECM or automatic transmission control
module (TCM) in
"limp home" mode.
ignition key ON before cranking (bulb
check function).
OED
II fault memory (including the MIL) can only be reset
using a special scan tool. Removing the connector from the
ECM or disconnecting the battery does not erase the fault
memory.

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- -
On-Board Diagnostics
Professional diagnostic scan tools available atthe time of this
printing include the BMW factory tools
(DISplus, GTI,
MoDiC) and a small number of aftermarket BMW-specific
tools. See
020 Maintenance.
In addition to the professional line of scan tools, inexpensive
generic OBD
II scan tool software programs and handheld
units are readily available. Though limited, they are
nonetheless powerful diagnostic tools. These tools read live
data streams and freeze frame data as well as a host of other
valuable diagnostic data.
Diagnostic monitors
Diagnostic monitors run tests and checks on specific
emission control systems, components, and functions.
A complete drive cycle is requiredforthe tests to bevalid. See
Drive cycle in this repair group. The diagnostic monitor
signals the
ECM of the loss or impairment of the signal or
component and determines if a signal or sensor is faulty
based on
3 conditions:
* Signal or component shorted to ground
Signal or component shorted to
B+
Signal or component missing (open circuit)
The OBD
II system monitors all emission control systems that
are installed. Emission control systems vary by vehicle model
and year. For example, a vehicle may not be equipped with
secondary air injection, so no secondary air readiness code
would be present.
OBD
II software monitors the following:
Oxygen sensors
Catalysts
Engine misfire
- Fuel tank evaporative control system
Secondary air injection Fuel system
Oxygen sensor monitoring. When driving conditions allow,
response rate and switching time of each oxygen sensor is
monitored. The oxygen sensor heater function is also
monitored. The OBD
II system differentiates between
precataylst and post-catalyst oxygen sensors and reads each
one individually. In order
forthe oxygen sensor to be
effectively monitored, the system must be in closed loop
operation.

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OBD-6
On-Board Diagnostics
Fuel system monitoring. This monitor looks at the fuel
delivery needed (long
/short term fuel trim) for proper engine
operation based on programmed data. If too much or not
enough fuel is delivered over a predetermined time, a DTC is
set and the MIL illuminates.
Fuel trim refers to adiustments to base fuel schedule.
Lono- ., term fuel trim refers to gradual adjustments to the fuel
calibration adjustment as compared to short term fuel trim.
Long term fuel trim adjustments compensate for gradual
changes that occur over time.
Fuel system monitoring monitors the calculated injection time
(ti) in relation to enginespeed, load and precatalyticconverter
oxygen
sensor(s) signals.
Using this data, the system optimizes fuel delivery for all
engine operating conditions.
Evaporative system monitoring. This monitor checks the
the fuel storage system and related fuel lines for leaks. It can
detect very small leaks anywhere in the system.
A leak detection unit (LDP or DMTL) is used to pressurize the
evaporative control system on a continuous basis (as the
drive cycle allows) and to
check system integrity.
Drive cycle
The OED II drive cycle is an important concept in
understanding OBD
II requirements. The purpose of the drive
cycle is to run ail of the emission-related on-board diagnostics
over a broad range of driving conditions.
A drive cycle is considered complete when all of the
diagnostic monitors have run their tests without interruption.
~ora drive cycle to be initiated, the vehicle must be started
cold and brought up to
1 60°F and at least 40°F above its
original starting temperature.
Readiness codes
Inspection/maintenance (I/M) readiness codes are mandated
as part of OBD
II. The readiness code is stored aftercomplete
diagnostic monitoring of specified components and systems
is carried out. The readiness code function was designed to
prevent manipulating an
I/M emission test procedure by
clearing faults codes or disconnecting the ECM or battery.

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On-Board Diagnostics
Readiness codes indicate whether the OED Ii system is
actually ready to monitor the various emission control
systems on the vehicle. The vehicle must complete a drive
cycle to set readiness codes. The code is binary:
0 for ready
1 for not ready
f
4 The parameters which are monitored for readiness are:
llM readiness codes
1. Catalyst efficiency
2. Catalyst heating
3. Fuel tank evaporative control
4. Secondary air injection
5.
NC refrigerant
6. Oxygen sensors
7. Oxygen sensor heaters
8. Exhaust gas recirculation
Readiness codes are set to 1 (not ready) in the following
cases:
~9~~.f~[<+t~t~p:,~;:#j~~{]~y~ ,,... , , 8701Dbd001
The battery or ECM is disconnected.
When
all zeros are displayed, the system has established
DTCs are erased after completion of repairs and a drive
cycle is not completed.
readiness. Readiness codes
can be displayed using BMW
and aftermarket scan tools.
An
OED II scan tool can be used to determine IIM readiness.
Diagnostic trouble codes (DTCs)
SAE standard J2012 mandates a 5-digit diagnostic trouble
code (DTC) standard. Each digit represents a specific value.
Emission related DTCs
start with the letter P for power train.
When the engine service
light (MIL) is illuminated it indicates
that a DTC has been stored.
DTCs are stored as soon as they occur, whether or not the
engine service light illuminates.
DTCs store and display a time stamp.
DTCs record the current fault status: Present, not currently
present, or intermittent.

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OBD-8
I On-Board Diagnostics
DTC digit interpretation
1st digit
P powertrain
B body
C chassis
2nd digit
0 SAE
1 BMW
3rd digit
0
1
2
3
4
5
6
7
4th - 5th digits total
system
airlfuei induction
fuel injection
ignition system or misfire
auxiliary emission control
vehicle speed
& idle control
ECM
inputs/outputs
transmission
individual circuits or
components
DTC example: P 0 3 0 6
P: A powertrain problem
0: SAE sanctioned or 'generic'
a 3: Related to an ignition system / misfire
06 Misfire detected at cylinder #6
DTCs provide a freeze frame or snap-shot of a vehicle
performance or emissions fault at the moment that the fault
first occurs. This information is accessible through generic
OED I1 scan tools.
Freeze frame data contains, but is not limited to, the following
information:
Engine load (calculated)
Engine rpm
Short and
long term fuel trim
Vehicle speed
Coolant temperature Intake manifold pressure
Open/closed loop operation
Fuel pressure (if available)
DTC