1999 LAND ROVER DISCOVERY light

EMISSION CONTROL - V8
17-2-40 DESCRIPTION AND OPERATION
To maintain driveability and effective emission control, EVAP canister purging must be closely controlled by the
engine management ECM, as a 1% concentration of fuel vapour from the EVAP canister in the air intake may shift
the air:fuel ratio by as much as 20%. The ECM must purge the fuel vapour from the EVAP canister at regular intervals
as its storage capacity is limited and an excessive build up of evaporated fuel pressure in the system could increase
the likelihood of vapour leaks. Canister purging is cycled with the fuelling adaptation as both cannot be active at the
same time. The ECM alters the PWM signal to the purge valve to control the rate of purging of the canister to maintain
the correct stoichiometric air:fuel mixture for the engine.
Fuel Leak Detection System Operation (vacuum type) – NAS only
The advanced evaporative loss control system used on NAS vehicles is similar to the standard system, but also
includes a CVS valve and fuel tank pressure sensor and is capable of detecting holes in the fuel evaporative system
down to 1 mm (0.04 in.). The test is carried out in three parts. First the purge valve and the canister vent solenoid
valve closes off the storage system and the vent pressure increases due to the fuel vapour pressure level in the tank.
If the pressure level is greater than the acceptable limit, the test will abort because a false leak test response will
result. In part two of the test, the purge valve is opened and the fuel tank pressure will decrease due to the depression
from the intake manifold, evident at the purge port of the EVAP canister during purge operation. In part three of the
test, the leak measurement test is performed. The pressure response of the tests determines the level of leak, and if
this is greater than the acceptable limit on two consecutive tests, the ECM stores the fault in diagnostic memory and
the MIL light on the instrument pack is illuminated. The test is only carried out at engine idle with the vehicle stationary,
and a delay of 15 minutes after engine start is imposed before diagnosis is allowed to commence.

EMISSION CONTROL - V8
DESCRIPTION AND OPERATION 17-2-41
EVAP System, Leak Detection Diagnostic (vacuum type)
The EVAP system leak detection is performed as follows:
1The ECM checks that the signal from the fuel tank pressure sensor is within the expected range. If the signal is
not within range, the leakage test will be cancelled.
2Next the purge valve is held closed and the canister vent solenoid (CVS) valve is opened to atmosphere. If the
ECM detects a rise in pressure with the valves in this condition, it indicates there is a blockage in the fuel
evaporation line between the CVS valve and the EVAP canister, or that the CVS valve is stuck in the closed
position and thus preventing normalisation of pressure in the fuel evaporation system. In this instance, the
leakage test will be cancelled.
3The CVS valve and the purge valve are both held in the closed position while the ECM checks the fuel tank
pressure sensor. If the fuel tank pressure sensor detects a decline in pressure, it indicates that the purge valve
is not closing properly and vapour is leaking past the valve seat face under the influence of the intake manifold
depression. In this instance, the leakage test will be cancelled.
4If the preliminary checks are satisfactory, a compensation measurement is determined next. Variations in fuel
level occur within the fuel tank, which will influence the pressure signal detected by the fuel tank pressure
sensor. The pressure detected will also be influenced by the rate of change in the fuel tank pressure, caused by
the rate of fuel evaporation which itself is dependent on the ambient temperature conditions. Because of these
variations, it is necessary for the ECM to evaluate the conditions prevailing at a particular instance when testing,
to ensure that the corresponding compensation factor is included in its calculations.
The CVS valve and purge valves are both closed while the ECM checks the signal from the fuel tank pressure
sensor. The rise in fuel pressure detected over a defined period is used to determine the rate of fuel evaporation
and the consequent compensation factor necessary.
5With the CVS valve still closed, the purge valve is opened. The inlet manifold depression present while the purge
valve is open, decreases EVAP system pressure and sets up a small vacuum in the fuel tank. The fuel tank
pressure sensor is monitored by the ECM and if the vacuum gradient does not increase as expected, a large
system leak is assumed by the ECM (e.g. missing or leaking fuel filler cap) and the diagnostic test is terminated.
If the EVAP canister is heavily loaded with hydrocarbons, purging may cause the air:fuel mixture to become
excessively rich, resulting in the upstream oxygen sensors requesting a leaner mix from the ECM to bring the
mixture back to the stoichiometric ideal. This may cause instability in the engine idle speed and consequently
the diagnostic test will have to be abandoned. The ECM checks the status of the upstream oxygen sensors
during the remainder of the diagnostic, to ensure the air:fuel mixture does not adversely affect the engine idle
speed.
6When the fuel tank pressure sensor detects that the required vacuum has been reached (-800 Pa), the purge
valve is closed and the EVAP system is sealed. The ECM then checks the change in the fuel tank pressure
sensor signal (diminishing vacuum) over a period of time, and if it is greater than expected (after taking into
consideration the compensation factor due to fuel evaporation within the tank, determined earlier in the
diagnostic), a leak in the EVAP system is assumed. If the condition remains, the MIL warning light will be turned
on after two drive cycles.
The decrease in vacuum pressure over the defined period must be large enough to correspond to a hole
equivalent to 1 mm (0.04 in.) diameter or greater, to be considered significant enough to warrant the activation
of an emissions system failure warning.
The diagnostic test is repeated at regular intervals during the drive cycle, when the engine is at idle condition. The
diagnostic test will not be able to be performed under the following conditions:
lDuring EVAP canister purging
lDuring fuelling adaption
lIf excess slosh in the fuel tank is detected (excess fuel vapour will be generated, invalidating the result)
Following the test, the system returns to normal purge operation after the canister vent solenoid opens. Possible
reasons for an EVAP system leak test failure are listed below:
lFuel filler not tightened or cap missing.
lSensor or actuator open circuit.
lShort circuit to vehicle supply or ground.
lEither purge or CVS valve stuck open.
lEither purge or CVS valve stuck shut or blocked pipe.
lPiping broken or not connected.
lLoose or leaking connection.

EMISSION CONTROL - V8
17-2-42 DESCRIPTION AND OPERATION
If the piping is broken forward of the purge valve or is not connected, the engine may run rough and fuelling adaptions
will drift. The fault will not be detected by the leak detection diagnostic, but it will be determined by the engine
management ECM through the fuelling adaption diagnostics.
The evaluation of leakage is dependent on the differential pressure between the fuel tank and ambient atmospheric
pressure, the diagnostic is disabled above altitudes of 9500 ft. (2800 m) to avoid false detection of fuel leaks due to
the change in atmospheric pressure at altitude.
Fuel Leak Detection System Operation (positive pressure leak detection type) – NAS only
The EVAP system with positive pressure leak detection capability used on NAS vehicles is similar to the standard
system, but also includes a fuel evaporation leak detection pump with integral solenoid valve. It is capable of detecting
holes in the EVAP system down to 0.5 mm (0.02 in.). The test is carried out at the end of a drive cycle, when the
vehicle is stationary and the ignition switch has been turned off. The ECM maintains an earth supply to the Main relay
to hold it on, so that power can be supplied to the leak detection pump.
First a reference measurement is established by passing the pressurised air through a by-pass circuit containing a
fixed sized restriction. The restriction assimilates a 0.5 mm (0.02 in) hole and the current drawn by the pump motor
during this procedure is recorded for comparison against the value to be obtained in the system test. The purge valve
is held closed, and the reversing valve in the leak detection pump module is not energised while the leak detection
pump is switched on. The pressurised air from the leak detection pump is forced through an orifice while the current
drawn by the pump motor is monitored.
Next the EVAP system diagnostic is performed; the solenoid valve is energised so that it closes off the EVAP system's
vent line to atmosphere, and opens a path for the pressurised air from the leak detection pump to be applied to the
closed EVAP system.
The current drawn by the leak detection pump is monitored and checked against that obtained during the reference
measurement. If the current is less than the reference value, this infers there is a hole in the EVAP system greater
than 0.5 mm (0.02 in) which is allowing the positive air pressure to leak out. If the current drawn by the pump motor
is greater than the value obtained during the reference check, the system is sealed and free from leaks. If an EVAP
system leak is detected, the ECM stores the fault in diagnostic memory and the MIL light on the instrument pack is
illuminated.
On NAS vehicles, the ECM works on a 2 trip cycle before illuminating the MIL. On EU-3 vehicles, the ECM works on
a 3 trip cycle before illuminating the MIL.
Following the test, the solenoid valve is opened to normalise the EVAP system pressure and the system returns to
normal purge operation at the start of the next drive cycle. Possible reasons for an EVAP system leak test failure are
listed below:
lFuel filler not tightened or cap missing.
lSensor or actuator open circuit.
lShort circuit to vehicle supply or ground.
lEither purge or solenoid valve stuck open.
lEither purge or solenoid valve stuck shut.
lBlocked pipe or air filter.
lPiping broken or not connected.
lLoose or leaking connection.
If the piping is broken forward of the purge valve or is not connected, the engine may run rough and fuelling adaptions
will drift. The fault will not be detected by the leak detection test, but will be determined by the engine management
ECM through the fuelling adaption diagnostics. This test can be run from TestBook/T4.

ENGINE MANAGEMENT SYSTEM - V8
18-2-6 DESCRIPTION AND OPERATION
Description - engine management
General
The V8 engine is equipped with the Bosch Motronic M5.2.1 engine management system. This system is a sequential
multiport fuel injection system controlled by an Engine Control Module (ECM).
A single ECM is used for the control of the existing 4.0 litre engine and the new 4.6 litre engine introduced with 03
model year vehicles for the NAS market only. The ECM contains the tunes for both engines variants. When the ECM
is replaced, TestBook/T4 must be used to select the correct tune to match the engine fitment.
The ECM has On Board Diagnostic (OBD) strategies as required by various market legislative bodies. To meet these
requirements the system monitors and reports on any faults that cause excessive exhaust emissions.
In markets that mandate OBD, the ECM monitors performance of the engine for misfires, catalyst efficiency, exhaust
leaks and evaporative control loss. If a fault occurs, the ECM stores the relevant fault code and warns the driver of
component failure by illuminating the Malfunction Indicator Light in the instrument pack.
In markets where OBD is not mandatory, the ECM will still monitor performance of the engine and store the fault code,
but will not illuminate the Malfunction Indicator Light.
The ECM uses input and output information from its sensors and actuators to control the following engine conditions:
lFuel quantity.
lClosed loop fuelling.
lOpen loop fuelling.
lIgnition timing.
lKnock control.
lIdle speed control.
lEmission control.
lOn-Board Diagnostic (OBD) where applicable.
lVehicle immobilisation.
lMisfire detection (where applicable).
lVehicle speed signal.
lRough road signal (where applicable).
lLow fuel level signal (where applicable).
lCoolant temperature gauge signal.
The ECM processes sensor information from the following input sources:
lIgnition switch (position II).
lCrankshaft speed and position sensor.
lCamshaft position sensor.
lEngine coolant temperature sensor.
lMass air flow sensor.
lIntake air temperature sensor.
lKnock sensor.
lThrottle position sensor.
lHeated oxygen sensors.
lHigh/ Low ratio switch.
lFuel tank pressure sensor (where fitted)
lThermostat monitoring sensor (where fitted)

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-49
Operation - engine management
Fuel quantity
The ECM controls engine fuel quantity by providing sequential injection to the cylinders. Sequential injection allows
each injector to deliver fuel to the cylinders in the required firing order.
To achieve optimum fuel quantity under all driving conditions, the ECM provides an adaptive fuel strategy.
Conditions
Adaptive fuel strategy must be maintained under all throttle positions except:
lCold starting.
lHot starting.
lWide open throttle.
lAcceleration.
All of the throttle positions mentioned above are deemed to be 'open loop'. Open loop fuelling does not rely on
information from the HO
2 sensors, but the air/ fuel ratio is set directly by the ECM. During cold start conditions the
ECM uses ECT information to allow more fuel to be injected into the cylinders to facilitate cold starting. This strategy
is maintained until the HO
2 sensors are at working temperature and can pass exhaust gas information to the ECM.
Because of the specific nature of the other functions e.g. hot starting, idle, wide open throttle, and acceleration they
also require an 'open loop' strategy. For NAS vehicles with secondary air injection for cold start conditions, refer to
the Emissions section.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Secondary Air Injection System.
Adaptive fuel strategy also allows for wear in the engine and components, as well as slight differences in component
signals, as no two components will give exactly the same readings.
Function
To be able to calculate the amount of fuel to be injected into each cylinder, the ECM needs to determine the amount
of air mass drawn into each cylinder. To perform this calculation, the ECM processes information from the following
sensors:
lMass air flow (MAF) sensor.
lCrank speed and position (CKP) sensor.
lEngine coolant temperature (ECT) sensor.
lThrottle position (TP) sensor.
During one engine revolution, 4 of the 8 cylinders draw in air. The ECM uses CKP sensor information to determine
that one engine revolution has taken place, and the MAF sensor information to determine how much air has been
drawn into engine. The amount of air drawn into each cylinder is therefore 1/4 of the total amount measured by the
ECM via the MAF sensor.
The ECM refers the measured air mass against a fuel quantity map in its memory and then supplies an earth path to
the relevant fuel injector for a period corresponding to the exact amount of fuel to be injected into the lower inlet
manifold. This fuel quantity is in direct relation to the air mass drawn into each cylinder to provide the optimum ratio.
During adaptive fuelling conditions, information from the heated oxygen sensors (HO
2S) is used by the ECM to correct
the fuel quantity to keep the air/ fuel ratio as close to the stoichiometric ideal as possible.
Closed loop fuelling
The ECM uses a closed loop fuelling system as part of its fuelling strategy. The operation of the three-way catalytic
converter relies on the ECM being able to optimise the air/ fuel mixture, switching between rich and lean either side
of lambda one. Closed loop fuelling is not standard for all markets, vehicles that are not fitted with HO
2S do not have
closed loop fuelling.
The ideal stoichiometric ratio is represented by λ =1. The ratio can be explained as 14.7 parts of air to every 1 part of
fuel.

ENGINE MANAGEMENT SYSTEM - V8
18-2-50 DESCRIPTION AND OPERATION
Conditions
To achieve closed loop fuelling, the ECM interacts with the following components:
lHO
2S.
lFuel injectors.
Closed loop fuelling is a rolling process controlled by the ECM. The ECM uses information gained from the CKP, ECT,
MAF/ IAT and the TP sensors, to operate under the following conditions:
lPart throttle.
lLight engine load.
lCruising.
lIdle.
Function
When the engine is operating in the above conditions, the ECM implements the closed loop fuelling strategy. The air/
fuel mixture is ignited by the high tension (ht) spark in the combustion chambers and the resulting gas is expelled into
the exhaust pipe. Upon entering the exhaust pipe the exhaust gas passes over the protruding tip of the HO
2S. The
HO
2S measures the oxygen content of the gas compared to that of ambient air and converts it into a voltage, which
is measured by the ECM.
The voltage signal read by the ECM is proportional to the oxygen content of the exhaust gas. This signal can then be
compared to stored values in the ECM's memory and an adaptive strategy can be implemented.
If the HO
2S informs the ECM of an excess of oxygen (lean mixture), the ECM extends the opening time of the fuel
injectors via the Injector Pulse Width (IPW) signal. Once this new air/ fuel ratio has been 'burnt' in the combustion
chambers the HO
2S can again inform the ECM of the exhaust gas oxygen content, this time there will be a lack of
oxygen or a rich mixture. The ECM reduces the opening time of the injectors via the IPW signal using the ECM's
adaptive fuel strategy. During closed loop fuelling the HO
2S will constantly switch from rich to lean and back again,
this indicates that the ECM and the HO
2S are operating correctly.
Open loop fuelling
Open loop fuelling does not rely on information from the HO
2S, but the air/ fuel ratio is set directly by the ECM, which
uses information gained from the ECT, MAF/ IAT, the TP sensors and also the vehicle speed sensor (VSS). The ECM
uses open loop fuelling under the following conditions:
lCold start.
lHot start.
lWide open throttle.
lAcceleration.
The ECM uses open loop fuelling to control fuel quantity in all non adaptive strategy conditions. The ECM implements
fuelling information carried in the form of specific mapped data contained within its memory.
Because there is no sensor information (e.g. HO
2S), provided back to the ECM, the process is called an 'open loop'.
The ECM will also go into open loop fuelling if a HO
2S fails.
Ignition timing
The ignition timing is an important part of the ECM adaptive strategy. Ignition is controlled by a direct ignition system
using two four-ended coils operating on the wasted spark principle.
When the ECM triggers an ignition coil to spark, current from the coil travels to one spark plug, then jumps the gap at
the spark plug electrodes, igniting the mixture in the cylinder in the process. Current continues to travel along the earth
path (via the cylinder head) to the spark plug negative electrode at the cylinder that is on the exhaust stroke. The
current jumps across the spark plug electrodes and back to the coil completing the circuit. Since it has simultaneously
sparked in a cylinder that is on the exhaust stroke, it has not provided an ignition source there and is consequently
termed 'wasted'.

ENGINE MANAGEMENT SYSTEM - V8
18-2-52 DESCRIPTION AND OPERATION
Evaporative emission control
Due to increasing legislation, all new vehicles must be able to limit evaporative emissions (fuel vapour) from the fuel
tank.
The ECM controls the emission control system using the following components:
lEVAP canister.
lPurge valve.
lCanister vent solenoid (CVS) valve – (NAS vehicles with vacuum type EVAP system leak detection capability
only)
lFuel tank pressure sensor – (NAS vehicles with vacuum type EVAP system leak detection capability only)
lFuel leak detection pump – (NAS vehicles with positive pressure type EVAP system leak detection capability
only)
lInterconnecting pipe work.
Refer to Emissions section for operating conditions of evaporative emission systems.

+ EMISSION CONTROL - V8, DESCRIPTION AND OPERATION, Evaporative Emission Control
Operation.
On-Board Diagnostics (OBD) - North American Specification vehicles only
The ECM monitors performance of the engine for misfires, catalyst efficiency, exhaust leaks and evaporative control
loss. If a fault occurs, the ECM stores the relevant fault code and warns the driver of component failure by illuminating
the Malfunction Indicator Light in the instrument pack.
On vehicles fitted with automatic gearbox, the ECM combines with the Electronic Automatic Transmission (EAT) ECU
to provide the OBD strategy.
Conditions
If the OBD function of the ECM flags a fault during its operation, it falls into one of the following categories:
lmin = minimum value of the signal exceeded.
lmax = maximum value of the signal exceeded.
lsignal = signal not present.
lplaus = an implausible condition has been diagnosed.
Function
All of the ECM's internal diagnostic fault paths are monitored by the OBD system. Specific faults have their own
numeric code relating to certain sensors or actuators etc. These specific faults fall into two types, error codes (E xxx)
or cycle codes (Z xxx). E codes represent instantaneous faults and Z codes relate to codes generated after completion
of a drive cycle.
If an emission relevant fault occurs on a drive cycle, the ECM stores a temporary fault code, if the fault does not occur
on subsequent drive cycles the fault code stays as a temporary fault code. If the fault recurs on subsequent drive
cycles the ECM stores the fault code as a permanent code, and depending on which component has failed the ECM
will illuminate the MIL.
Immobilisation system
The ECM and the body control unit (BCU) security system comprise the immobilisation system.
The ECM and the BCU combine to prevent the engine from running unless the appropriate security criteria are met.
The ECM and the BCU are a matched pair, if either one is replaced for any reason, the system will not operate unless
the replaced unit is correctly matched to its original specification. TestBook must be used to reconfigure the
immobilisation system.
Conditions
The ECM operates immobilisation in three states:
l'New'.
l'Secure'.
l'No Code'.

ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-53
Function
With the ECM operating in the 'New' state, TestBook is required to instruct the ECM to learn the new BCU code. If the
ECM is in delivery state (i.e. direct from the supplier), it will not run the vehicle and will store a new ECM fault code
when it is fitted. This code must be cleared after instructing the ECM to learn the BCU code using TestBook.
When the ECM is in the 'Secure' state, no further action is required as the ECM has successfully learned the BCU
code. A 'Secure' ECM can not be configured to a 'No Code' state.
If the vehicle is fitted with an ECM with a valid code, the engine will start and the MIL will go out.
However, if the ECM has an invalid BCU security code the engine will crank, start, and then immediately stall. The
status of the security system can only be interrogated using TestBook.
TestBook is able to retrieve the following immobilisation fault codes:
Misfire detection
Due to increasing legislation, all new vehicles must be able to detect two specific levels of misfire.
Conditions
The ECM is able to carry out misfire detection as part of the OBD system using the following component parts:
lFlywheel reluctor adaptation.
lCalculation of engine roughness.
lDetection of excess emissions misfire.
lDetection of catalyst damaging misfire.
Function
The flywheel/ reluctor ring is divided into four segments 90° wide. The ECM misfire detection system uses information
generated by the CKP to determine crankshaft speed and position. If a misfire occurs, there will be an instantaneous
slight decrease in engine speed. The ECM misfire detection system is able to compare the length of time each 90°
segment takes and is therefore able to pinpoint the source of the misfire.
For the ECM misfire detection system to be calibrated for the tolerances of the reluctor tooth positions, the flywheel/
reluctor ring must be 'adapted' as follows:
l1800 - 3000 rev/min = speed range 1.
l3000 - 3800 rev/min = speed range 2.
l3800 - 4600 rev/min = speed range 3.
l4600 - 5400 rev/min = speed range 4.
The ECM carries out flywheel/ reluctor ring adaptions across all the above speed ranges and can be monitored by
TestBook. The test should be carried out as follows:
lEngine at normal operating temperature.
lSelect second gear (for both automatic and manual transmission vehicles).
lAccelerate until engine rev limiter is operational.
lRelease throttle smoothly to allow engine to decelerate throughout the speed ranges.
lRepeat process as necessary until all adaptations are complete.
P Code J2012 Description Land Rover Description
P1666 Engine anti-theft signal circuit malfunction BCU serial link frame/ bit timing error
P1667 Engine anti-theft signal circuit low Serial link short circuit to earth
P1668 Engine anti-theft signal circuit high Serial link open circuit
P1672 Engine anti-theft signal circuit wrong code
receivedSecure ECM, received incorrect code
P1673 Engine anti-theft signal new engine control
module not configuredNew ECM fitted
P1674 Engine anti-theft signal No code ECM, valid code received