1999 LAND ROVER DISCOVERY lock

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-37
There are eight IACV diagnostic checks performed by the ECM:
lOutput short circuit to earth – opening coil
lOutput short circuit to battery supply – opening coil
lOutput open circuit – opening coil
lOutput short circuit to earth – closing coil
lOutput short circuit to battery voltage – closing coil
lOutput open circuit – closing coil
lBlocked IACV – rev/min error low (engine speed must be 100 rev/min less than the target speed, engine load
less than 2.5 and the measured air flow more than 10 kg/h less than the expected air flow for a fault condition to
be flagged).
lBlocked IACV – rev/min error high (the engine speed must be more than 180 rev/min greater than the target
speed and the measured air flow more than 10 kg/h greater than the expected air flow for a fault condition to be
flagged).
Should a malfunction of the component occur, the following fault codes may be evident and can be retrieved by
TestBook.
P Code J2012 Description Land Rover Description
P1510 IACV opening coil malfunction Short circuit to battery supply - opening winding
P1513 IACV opening coil malfunction Short circuit to earth - opening winding
P1514 IACV opening coil malfunction Open circuit - opening winding
P1553 IACV closing coil malfunction Short circuit to battery supply - closing winding
P1552 IACV closing coil malfunction Short circuit to earth - closing winding
P1551 IACV closing coil malfunction Open circuit - closing winding
P0505 Idle control system malfunction Blocked IACV - high or low rev/min error

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-51
Conditions
The ECM calculates ignition timing using input from the following:
lCKP sensor.
lKnock sensors (KS).
lMAF sensor.
lTP sensor (idle only).
lECT sensor.
Function
At engine start up, the ECM sets ignition timing dependent on ECT information and starting rev/min from the CKP. As
the running characteristics of the engine change, the ignition timing changes. The ECM compares the CKP signal to
stored values in its memory, and if necessary advances or retards the spark via the ignition coils.
Ignition timing is used by the ECM for knock control.
Knock control
The ECM uses active knock control to prevent possible engine damage due to pre-ignition. This is achieved by
converting engine block noise into a suitable electrical signal that can be processed by the ECM. A major contributing
factor to engine 'knock' is fuel quality, the ECM can function satisfactorily on 91 RON fuel as well as the 95 RON fuel
that it is calibrated for.
Conditions
The ECM knock control system operates as follows:
lHot running engine.
l91 or 95 RON fuel.
Function
The ECM knock control uses two sensors located one between the centre two cylinders of each bank. The knock
sensors consist of piezo ceramic crystals that oscillate to create a voltage signal. During pre-ignition, the frequency
of crystal oscillation increases which alters the signal output to the ECM.
If the knock sensors detect pre-ignition in any of the cylinders, the ECM retards the ignition timing by 3° for that
particular cylinder. If this action stops the engine knock, the ignition timing is restored to its previous figure in
increments of 0.75°. If this action does not stop engine knock then the ECM retards the ignition timing a further 3° up
to a maximum of -15° and then restores it by 0.75° and so on until the engine knock is eliminated.
The ECM also counteracts engine knock at high intake air temperatures by retarding the ignition as above. The ECM
uses the IAT signal to determine air temperature.
Idle speed control
The ECM regulates the engine speed at idling. The ECM uses the idle air control valve (IACV) to compensate for the
idle speed drop that occurs when the engine is placed under greater load than usual. When the throttle is in the rest
position i.e. it has not been pressed, the majority of intake air that the engine consumes comes from the idle air control
valve.
IACV control idle speed
Conditions in which the ECM operates the IACV control idle speed is as follows:
lIf any automatic transmission gears other than P or N are selected.
lIf air conditioning is switched on.
lIf cooling fans are switched on.
lAny electrical loads activated by the driver.
Function
The idle air control valve utilises two coils that use opposing pulse width modulated (PWM) signals to control the
position of a rotary valve. If one of the circuits that supplies the PWM signal fails, the ECM closes down the remaining
signal preventing the idle air control valve from working at its maximum/ minimum setting. If this should occur, the idle
air control valve assumes a default idle position at which the engine idle speed is raised to 1200 rev/min with no load
placed on the engine.

ENGINE MANAGEMENT SYSTEM - V8
18-2-62 DESCRIPTION AND OPERATION
Cruise control block diagram
1SLABS ECU
2BCU
3Cruise control master switch
4SET+ switch
5RES switch
6Brake pedal switch7Clutch pedal switch
8Cruise control ECU
9Vacuum pump assembly incorporating
pneumatic actuator
10Automatic gear selector lever

ENGINE MANAGEMENT SYSTEM - V8
18-2-70 DESCRIPTION AND OPERATION
Body control unit
On manual gearbox vehicles, the BCU provides cruise control lockout or suspend function as described under brake
pedal switch.
On vehicles with automatic gearbox, the BCU monitors the status of the brake pedal switch as well as the status of
the automatic gearbox gear selector lever. The BCU monitors the gear selector lever to determine which gearbox
position the driver has selected. If the BCU detects that the driver has selected park, reverse or neutral, it sends a
signal to the cruise control ECU which inhibits cruise operation or deactivates cruise control if it is activated.
Input/Output
If the BCU receives a brake pedal switch signal or an automatic gearbox gear selector lever position signal, the BCU
sends a HIGH signal to the cruise control ECU. The cruise control ECU cancels or inhibits cruise control functions.

ENGINE MANAGEMENT SYSTEM - V8
ADJUSTMENTS 18-2-77
ADJUST ME NTS
Cable - throttle
$% 19.20.05
Adjust
1.Loosen outer cable locknuts.
2.Adjust the rear locknut until it is in contact with
the back of the abutment bracket, and the gap
between the throttle and the inner driven lever
is 0.5 mm ± 0.4 mm (0.020 ± 0.015 in).
3.Tighten cable front nut to lock cable to
abutment bracket.
Cable - cruise control
$% 19.75.11
Adjust
1.Ensure that the throttle cable is correctly
adjusted.

+ ENGINE MANAGEMENT SYSTEM -
V8, ADJUSTMENTS, Cable - throttle.
2.Loosen outer cable locknuts.
3.Adjust the rear locknut to obtain a 4.0 to 4.5
mm (0.157 to 0.177 in) gap, dimension 'A',
between the cruise control cable lever and the
throttle cable driven lever.
4.Tighten cable front locknut.

ENGINE MANAGEMENT SYSTEM - V8
REPAIRS 18-2-85
Knock sensor (KS)
$% 18.30.28
Remove
1.Release fixings and remove battery cover.
2.Disconnect battery earth lead.
3.Raise front of vehicle.
WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.
4.Remove fixings securing underbelly panel and
remove panel.
5.Disconnect multiplug from KS.
6.Remove nut securing KS to cylinder block and
remove KS. Refit
1.Clean mating faces of KS and cylinder block.
2.Fit KS to cylinder block and tighten nut to 22
Nm (16 lbf.ft).
3.Connect multiplug to KS.
4.Fit underbelly panel and secure with fixings.
5.Remove stand(s) and lower vehicle.
6.Connect battery earth lead.
7.Fit battery cover and secure the fixings.

ENGINE MANAGEMENT SYSTEM - V8
18-2-88 REPAIRS
Cable - throttle
$% 19.20.06
Remove
1.Release 3 fasteners and remove drivers side
closing panel and move aside.
2.Release inner cable from throttle pedal.
3.Release outer cable from bulkhead. 4.Release outer cable from clip, loosen lock nuts
and remove outer cable from abutment
bracket.
5.Release inner cable from operating lever and
remove cable.
Refit
1.Position cable, secure to bulkhead and
connect inner cable to throttle pedal.
2.Position inner cable to operating lever and
connect outer cable to abutment bracket and
retaining clip.
3.Position closing panel and secure fasteners.
4.Adjust throttle cable.

+ ENGINE MANAGEMENT SYSTEM -
V8, ADJUSTMENTS, Cable - throttle.

ENGINE MANAGEMENT SYSTEM - V8
18-2-96 REPAIRS
Cable - cruise control
$% 19.75.10
Remove
1.Release clip and disconnect inner cable from
actuator.
2.Release outer cable from actuator mounting
bracket.
3.Loosen cable locknuts, release outer cable
from abutment bracket and retaining clip.
4.Release inner cable from operating lever and
remove cable.
Refit
1.Position cable and connect to operating lever.
2.Position cable to abutment bracket.
3.Position outer cable to actuator mounting
bracket and connect inner cable to actuator.
4.Adjust cruise control cable.

+ ENGINE MANAGEMENT SYSTEM -
V8, ADJUSTMENTS, Cable - cruise control.
Switch - cruise control (on/off)
$% 19.75.30
Remove
1.Carefully remove switch from instrument cowl.
2.Disconnect multiplug and remove switch.
Refit
1.Position new switch and connect multiplug.
2.Carefully push switch into instrument cowl.