Engine Controls - Self-Diagnostics - with Codes: Overview Land Rover Discovery II

ECM CONNECTOR IDENTIFICATION

On Discovery Series II, ECM is located on the right side "A" post behind the front passenger kick panel. On Range Rover, the ECM is mounted in a plastic E-box located on the left side of engine compartment firewall. ECM is cooled by a dedicated fan, which provides cabin air to the plastic E-box maintaining a suitable environment for ECM operation. The operating temperature of the ECM is monitored by an internal temperature sensor. On all models, the ECM has 5 independent connectors totalling 134 pins. (Scheme 6)and (Scheme 7). See ECM CONNECTOR IDENTIFICATION table.

Scheme 6

Scheme 7

ECM CONNECTOR IDENTIFICATION

Description

DTCs P0100 and P0101 will set based on compared signals from the Mass Airflow (MAF)/Intake Air Temperature (IAT) sensors and the Throttle Position (TP) sensor. DTC P0100 will set if there is a mass or volume airflow circuit malfunction. If P0100 is set go to DTC P0102 & P0103: MASS OR VOLUME AIRFLOW CIRCUIT LOW/HIGH INPUT testing. DTC P0101 is a load monitoring DTC based on an unexpected throttle position ratio to airflow. DTC P0101 will set if there is a mass or volume airflow circuit range or performance problem. If DTC P0101 is set go to DTC P0120, P0122 & P0123: THROTTLE POSITION (TP) SENSOR CIRCUIT testing.

Note. Mass Airflow (MAF) and Intake Air Temperature (IAT) sensors are combined into a single unit and located between the air filter housing and the intake manifold. ECM uses input signals from the MAF/IAT sensor unit to calculate volume of air flowing into the engine.

MAF sensor uses a hot-film element to monitor mass of airflow being drawn into engine. There are 2 sensing elements, one element monitors ambient air temperature, while the other is heated to a temperature 360°F (200°C) more than ambient air temperature. When intake air passes the heated element, the temperature decreases, reducing the resistance of the hot-film element. In order to maintain the set temperature, the heated element circuit must supply more current. Changes in current are detected in the monitoring circuit. This change data is supplied to the ECM as a voltage between 0.0-5.0 volts. ECM interprets this data as a measure of the mass of airflow. The measured mass of airflow is used by the ECM to determine the amount of fuel to be injected for optimum engine performance and low emissions.

ECM checks MAF sensor for open circuit and confirms expected sensor output voltage at specific engine speeds. ECM will use a default value for airflow based on throttle position, engine speed and intake air temperature. A MAF sensor failure will result in hard engine starts, engine stalling after starting, engine idle speed control inoperative, poor throttle response and driveability, emissions control inoperative, MAF sensor signal offset, reduced engine performance, and/or a high long term fuel correction.

MAF sensor can fail or supply an incorrect signal in the following ways

1. Open in sensor harness.
2. Short to battery voltage in sensor harness.
3. Short to ground in sensor harness.
4. Contaminated or damaged sensor element.
5. Air leak after the MAF sensor.
6. Inlet air restriction.
7. Resistance in wiring harness causing signal offset.

The Intake Air Temperature (IAT) sensor uses a thermistor with a Negative Temperature Coefficient (NTC). As intake air temperature increases, IAT sensor resistance and output voltage decreases. If there is an IAT sensor failure, ECM will substitute a value of 113°F (45°C) for intake air temperature.

IAT sensor can fail or supply an incorrect signal in the following ways

1. Adaptive fueling is disabled.
2. Idle speed adaptation is disabled.
3. Catalyst monitoring affected due to exhaust temperature model.
4. Idle speed actuator test is disabled.
5. Warm up ignition angle is affected.
6. Condenser fan hot restart is inhibited.

IAT sensor can fail or supply an incorrect signal because of the following

1. Open in sensor harness.
2. Short to battery voltage in sensor harness.
3. Short to ground in sensor harness.
4. Increased sensor resistance.
5. Contaminated or damaged sensor element.

ECT sensor is located at top front of engine, next to upper coolant outlet pipe. ECT sensor have a Negative Temperature Coefficient (NTC) thermistor. As coolant temperature increases, sensor thermistor resistance decreases, as coolant temperature decreases, sensor thermistor resistance increases. ECM receives a 0.0-5.0 volt analog signal which is used to control fuel injector ON time during cold starting and warm-up (a richer mixture at low coolant temperatures and a leaner mixture at high coolant temperatures).

On Discovery Series II, ECT sensor uses one thermistor and a 4-pin connector with 2 wires. see scheme 5 ECM supplies the instrument cluster with a Pulse Width Modulated (PWM) coolant temperature signal temperature gauge operation. ECM provides ECT sensor with a 5-volt reference via ECM 52-pin connector C0636 terminal No. 22 (Green wire). ECM provides ECT sensor ground via ECM 52-pin connector C0636 terminal No. 21 (Red/Black wire). (Scheme 6)and (Scheme 7).

On Range Rover, ECT sensor uses 2 thermistors and a 4-pin connector with 4 wires. see scheme 5 ECM uses ECT sensor thermistor input signals from 2 wires to control fuel injector ON time. The other ECM sensor thermistor analog signals from the other 2 wires are used by the Body Control Module (BECM) to control engine temperature warning lamp operation on instrument cluster. ECM provides ECT sensor with a 5-volt reference via ECM 52-pin connector C0636 terminal No. 22 (Green/Blue wire). ECM provides ECT sensor ground via ECM 52-pin connector C0636 terminal No. 21 (Red/Black wire). (Scheme 6)and (Scheme 7).

On all models equipped with Secondary Air Injection (SAI), ECT sensor signal is monitored by ECM at engine start, to determine if the engine is cold enough to warrant SAI operation. ECT sensor is then monitored to switch off the SAI when required engine coolant temperature has been attained.

If there is an ECT sensor failure the ECM uses a changing default value during warm up based on Inlet Air Temperature (IAT) sensor signal. When strategy default value is 140°F (60°C), ECM implements a fixed ECT sensor default value of 185°F (85°C). It will also illuminate the MIL. An ECT sensor failure may result in a fast idle condition on initial start-up until normal operating temperature value is reached.

If there is an ECT sensor signal failure any of the following symptoms may be observed

1. Poor cold or warm/hot starting and driveability.
2. MIL will be illuminated.
3. Instrument cluster temperature warning lamp will be illuminated.
4. Temperature gauge reads excessively cold or hot.
5. Cooling fan will not operate.
6. Secondary Air Injection (SAI) pump will operate at engine start up even when engine is hot.

ECT sensor can fail or supply incorrect signal in the following ways

1. ECT sensor open circuit.
2. ECT sensor circuit short to battery voltage.
3. ECT sensor circuit short to ground.
4. Incorrect mechanical fitting.
5. An ECT sensor signal fixed at more than 104°F (40°C) will not be detected.
6. An ECT sensor signal fixed at less than 104°F (40°C) will not be detected.

TP sensor is located on the rear of the throttle body assembly in the engine compartment. TP sensor signal informs ECM of actual throttle position and rate of change in throttle position. ECM compares TP sensor output with Mass Airflow (MAF) sensor output. If values from these two sensors do not agree and fuel injection feedback indicates correct air/fuel mixture, ECM assumes MAF sensor is correct and TP sensor has failed. During deceleration when the ECM receives a closed throttle position signal from the TP sensor the ECM closes fuel injectors for as long as the throttle is closed.

The TP sensor signal is also used by the Electronic Automatic Transmission (EAT) ECU to determine correct points for gear shifts and acceleration kickdown. On Discovery Series II, ECM also supplies the Self-Leveling and ABS (SLABS) ECU and the Active Cornering Enhancement (ACE) ECU with TP sensor information as a PWM signal. On all models, the EAT ECU not seeing a TP signal will cause poor gear change quality, loss of kickdown or EAT ECU to select default transmission control.

If there is a TP sensor signal failure the ECM uses a default value derived from engine load and speed. A TP sensor failure may result in the following symptoms

1. Poor engine performance.
2. Delayed throttle response.
3. Emission control failure.
4. Closed loop idle speed control inoperative.
5. Automatic gearbox kickdown inoperative.
6. Incorrect altitude adaptation.
7. MIL illuminated.

TP sensor can fail or supply incorrect signal in the following ways

1. TP sensor open circuit.
2. Short to battery voltage or ground.
3. Signal out of parameters.
4. Restriction in air inlet or blocked air filter (load monitoring, ratio of the TP sensor to MAF sensor).
5. Vacuum leak.

There are 4 Heated Oxygen Sensors (HO2S) located in the exhaust system. Front HO2S (bank 1, sensor 1) is located in front of the left side catalytic converter. Rear HO2S (bank 1, sensor 2) is located after the left side catalytic converter. Front HO2S (bank 2, sensor 1) is located in front of the right side catalytic converter. Rear HO2S (bank 2, sensor 2) is located after the right side catalytic converter. Rear HO2S measure oxygen content after catalytic converters to monitor operating efficiency of converters.

Each HO2S is electrically heated to ensure sensor achieves operating temperature as quickly as possible after start-up. ECM energizes HO2S heater using a Pulse Width Modulation (PWM) signal which starts low and increases within 30 seconds to desired heater temperature. Primary HO2S heaters are wired in parallel and secondary HO2S heaters are wired in parallel for synchronous ECM control of each heater pair.

HO2S operating temperature is approximately 662°F (350°C). To achieve and maintain this temperature there is a heating element incorporated in HO2S which is controlled by a PWM signal from the ECM. The HO2S heating elements are activated immediately after engine start or during low engine load conditions when exhaust gas temperature is insufficient to maintain the required HO2S operating temperature. If the heater fails, the ECM will not allow closed loop fueling to be implemented until the sensor has achieved the required operating temperature. This value equates to an HO2S output signal of 450-500 mV. A richer mixture will increase HO2S output voltage towards 1000 mV. A leaner mixture decreases HO2S output voltage towards 100 mV. From cold start, ECM runs an open loop fueling strategy. ECM keeps this strategy in place until the HO2S is at a normal operating temperature. At this point the ECM starts to receive HO2S information and it can then switch into closed loop fueling as part of its adaptive strategy. The maximum operating temperature of the HO2S tip is 1706°F (930°C), temperatures greater than this will damage the sensor.

In the event of a HO2S signal failure any of the following symptoms may be observed

1. Default to open loop fueling on defective bank.
2. ECM will eventually default into open loop fueling.
3. High CO reading.
4. Excessive emissions.
5. Strong hydrogen sulfide smell like a strong smell of rotten eggs until the ECM defaults to open loop fueling.
6. MIL will be illuminated.

HO2S can fail in the following ways or supply incorrect signal

1. HO2S sensor open circuit.
2. Short circuit to battery voltage.
3. Short circuit to ground.
4. Sensor disconnected.
5. Stoichiometric ratio outside the correct operating band.
6. HO2S contamination from leaded fuel or other source.
7. Air leak into the exhaust system.
8. Wiring harness damage.
9. Sensors installed incorrectly or cross wired.

Note. Front and rear HO2S sensors are not interchangeable even though they can be mounted in reversed positions. The harness connections are different: Orange in front and Gray in rear. Connector signal terminals are gold plated and heater supply terminals are tin plated. Interchanging terminals will cause contamination and adversely affect system performance.

If front HO2S wiring is crossed over (LH bank to RH bank), engine will run normally after initial start up, but performance will become progressively worse as sensors go towards maximum rich for one bank of cylinders and maximum lean for the other. If front HO2S wiring is switched left for right, vehicle will operate properly until sensors reach operating temperature. ECM will then cause one bank of cylinders to run very rich and the other bank to run very lean. This will cause engine to misfire, idle rough and emit black smoke, with possible catalytic converter damage.

During adaptive fueling conditions, ECM uses information from HO2S to correct fuel quantity to keep air/fuel ratio as close to the stoichiometric ideal as possible. Closed loop fueling is used as part of ECM fueling strategy. The operation of the three-way catalytic converter relies on ECM being able to optimize the air/fuel mixture, switching between rich and lean either side of the stoichiometric ideal.

Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim.

Multiport Sequential Fuel Injection (SFI) system uses one fuel injector per cylinder. Fuel injectors are fitted between pressurized fuel rail and intake manifold. Each injector contains a solenoid controlled by ECM. When solenoid is energized, a plunger is pulled off its seat and allows pressurized fuel to spray into the intake manifold. Fuel injector total failure or a leak that causes a rich mixture will cause a misfire in affected cylinder.

On Discovery Series II, the fuel injectors are supplied with battery voltage through the main relay via fuse No. 1 (30-amp) located in engine compartment fuse box. On Range Rover, the fuel injectors are supplied with battery voltage through the main relay via fuse No. 37 (30-amp) located in engine compartment fuse box. On all models, fuel injector operation is controlled by the ECM through the ground path of each fuel injector. This facility allows the ECM to control the fuel injectors so that sequential fuel injection can take place.

Specific fuel injector failures will generate a specific DTC for suspect injector that are stored in the ECM as follows

Injector No. 1

1. DTC P0201 will set because of an open circuit.
2. DTC P0261 will set because of a short circuit to ground.
3. DTC P0262 will set because of a short to battery voltage.

Injector No. 2

1. DTC P0202 will set because of an open circuit.
2. DTC P0264 will set because of a short circuit to ground.
3. DTC P0265 will set because of a short to battery voltage.

Injector No. 3

1. DTC P0203 will set because of an open circuit.
2. DTC P0267 will set because of a short circuit to ground.
3. DTC P0268 will set because of a short to battery voltage.

Injector No. 4

1. DTC P0204 will set because of an open circuit.
2. DTC P0270 will set because of a short circuit to ground.
3. DTC P0271 will set because of a short to battery voltage.

Injector No. 5

1. DTC P0205 will set because of an open circuit.
2. DTC P0273 will set because of a short circuit to ground.
3. DTC P0274 will set because of a short to battery voltage.

Injector No. 6

1. DTC P0206 will set because of an open circuit.
2. DTC P0276 will set because of a short circuit to ground.
3. DTC P0277 will set because of a short to battery voltage.

Injector No. 7

1. DTC P0207 will set because of an open circuit.
2. DTC P0279 will set because of a short circuit to ground.
3. DTC P0280 will set because of a short to battery voltage.

Injector No. 8

1. DTC P0208 will set because of an open circuit.
2. DTC P0282 will set because of a short circuit to ground.
3. DTC P0283 will set because of a short to battery voltage.

The flywheel and reluctor ring are divided into four 90-degree segments. The ECM misfire detection system uses information from the Crankshaft Position (CKP) sensor to determine crankshaft speed and position. If a misfire occurs, there will be an instantaneous decrease in engine speed. The ECM is able to compare the length of time each 90-degree segment takes and is therefore able to pinpoint the source of the misfire.

The ECM performs misfire detection as part of OBD system using the following

1. Crankshaft Position (CKP) Sensor.
2. Calculation of engine roughness.
3. Detection of excess emissions misfire.
4. Detection of catalyst damaging misfire.

KS "A" is located on left side of engine block between cylinders No. 3 and No. 5, and KS "B" is located on right side of engine between cylinders No. 2 and No. 4. KS contains a piezoelectric ceramic element which produces a voltage proportional to engine vibration. ECM uses KS, Camshaft Position (CMP) sensor and Crankshaft Position (CKP) sensor signals to verify engine knock based on positions of cylinders. If CMP sensor fails, ECM will disable knock control. If knock control is disabled, ECM will default to a safe ignition map.

If a knock sensor should fail, the following symptoms may be observed

1. Possible rough running.
2. Reduction in engine performance.

CKP sensor is located on the left side of flywheel housing, below cylinder No. 7. A reluctor ring mounted to flywheel is used to generate a the CKP signal. CKP sensor provides ECM with information indicating that engine is turning, engine speed and crankshaft position during engine cycle. ECM controls fuel injection and coil firing based on signal from CKP sensor. Engine overspeed protection is set at 5500 RPM and is based on CKP sensor signal.

The tip of the CKP sensor protrudes through an aperture in the engine block rear flange, adjacent to the outer circumference of the flywheel. A 60-tooth reluctor ring is mounted to the flywheel which provides the reference signal to the CKP sensor. The output voltage varies in proportion to engine speed. The reluctor ring has a set tooth pattern, 60 teeth are spaced at 6 degrees intervals and are 3 degrees wide. Two teeth are removed to provide a reference mark at 60° BTDC for No. 1 cylinder. There is no back up strategy or limp home mode if sensor fails, the engine will stop or will not start.

There is no default strategy for the CKP sensor. In the event of a CKP sensor signal failure any of the following symptoms may be observed

1. Engine cranks but fails to start.
2. MIL remains on at all times.
3. Engine misfires (CKP sensor incorrectly fitted).
4. Engine runs roughly or even stalls (CKP sensor incorrectly fitted).
5. Tachometer fails to operate.

If a CKP sensor should fail, the following DTCs may be set

1. If DTC P0335 is set, the reference mark is outside search window when engine speed is more than 500 RPM for more than 2 revolutions.
2. If DTC P0336 is set, the incorrect number of teeth have been detected plus or minus one tooth between reference marks when engine speed is more than 500 RPM.

CMP sensor is a Hall Effect sensor located in the engine front cover, above and behind the crankshaft pulley. CMP sensor produces 4 pulses for every 2 revolutions of the engine (one pulse is slightly longer than the others). CMP sensor is positioned close to the camshaft gear wheel, the gear wheel has 4 slots machined at 90 degree intervals. This allows ECM to recognize 4 individual cylinders every camshaft revolution or all 8 cylinders every crankshaft revolution. CMP sensor Hall effect works as a magnetic switch. It switches battery voltage on or off depending on the position of the camshaft gear wheel in relationship to the sensor. The ECM uses this signal for cylinder recognition to control sequential fuel injection, engine knock and diagnostic purposes.

If CMP sensor fails, default strategy is to continue normal ignition timing. Fuel injection timing will default to bank control based on top dead center timing. Injection timing will either be correct or one revolution out of synchronization. Individual cylinder knock control will be disabled and misfire identification may be incorrect. There may not be a driveability problem with a fault being indicated by illumination of the MIL.

The CKP sensor failure must be detected for more than 100 cam pulses (25 engine revolutions) when engine speed is greater than 500 RPM. If there is a CMP sensor signal failure any of the following symptoms may be observed

1. Ignition timing reverts to default values from ECM memory.
2. Loss of cylinder correction and/or active knock control.
3. Loss of active knock control diagnostics.
4. Loss of cylinder identification for misfire diagnostics.
5. Loss of quick synchronization of crankshaft and camshaft for cranking/start up.
6. Fuel injection could be 360 degrees out of phase.
7. Front HO2S sensor aging period diagnostic disabled.

Secondary Air Injection (SAI) system is used to supply additional air to the exhaust system, just behind the exhaust valves. This additional air is used to decrease amount time required for catalytic converters to reach normal operating temperature. SAI system includes a SAI pump, SAI vacuum solenoid valve, 2 SAI control valves (1 for each bank of cylinders), SAI pump relay, vacuum reservoir, vacuum harness and pipes. see scheme 10or see scheme 11.

When engine is started the ECM checks engine coolant temperature. If engine coolant temperature is less than 131°F (55°C), ECM will activate SAI pump. SAI pump will operate for approximately 95 seconds when engine coolant temperature is 46°F (8°C) and approximately 30 seconds when engine coolant temperature is 131°F (55°C). ECM can cancel SAI pump operation if engine speed or load is excessive.

When ECM energizes the SAI pump, the ECM energizes the SAI vacuum solenoid valve, which opens the SAI vacuum valve. When vacuum valve opens vacuum from the reservoir is applied to the vacuum operated SAI control valves on each side of the engine. When vacuum is applied the SAI control valves open simultaneously and allow air from SAI pump through to the exhaust ports. Secondary air is injected into the inner most exhaust ports on each bank.

When ECM breaks the ground circuit to de-energize SAI vacuum solenoid valve, the vacuum supply to the SAI control valves is cut off and the valves close to prevent further air being injected into the exhaust manifold. At the same time as the SAI vacuum solenoid valve is closed, the ECM opens the ground circuit to the SAI pump relay, to stop the SAI pump. A vacuum reservoir is included in the vacuum line between the intake manifold and the SAI vacuum solenoid valve. This prevents changes in vacuum pressure from the intake manifold being passed on to cause fluctuations of the secondary air injection solenoid valve. The vacuum reservoir contains a one way valve and ensures a constant vacuum is available for the SAI vacuum solenoid valve operation. This is particularly important when the vehicle is at high altitude.

There are 2 Heated Oxygen Sensors (HO2S) mounted at rear of each catalytic converter. The rear HO2S are used to monitor catalyst efficiency. If the left bank catalyst efficiency has deteriorated DTC P0420 will set. If the right side catalyst efficiency has deteriorated DTC P0430 will set. In either case the MIL will be illuminated.

When the ECM grounds EVAP purge valve, the valve opens to allow fuel vapors stored in the EVAP canister to be purged to the engine intake manifold. If the EVAP purge valve malfunctions or sticks in the open or closed position, the EVAP system will cease to function. A DTC will be set and the MIL will be illuminated if the valve status is unchanged for 45 seconds after engine has been running for 15 minutes. The ECM does not have a default operation available. If the purge valve is stuck open, a rich air fuel mixture is likely to result, causing engine misfire and fueling adaptations to change.

ECM must control EVAP system purging to maintain driveability and effective emission control. An unexpected one percent concentration of fuel vapor from the EVAP canister added to intake air can shift the air fuel ratio by as much as 20 percent. ECM must purge fuel vapor from EVAP canister at regular intervals to prevent excessive build-up of fuel pressure in system and possible vapor leaks. Canister purging is cycled with fueling adaptation because both cannot be active at the same time. ECM alters purge valve PWM signal to control purging rate of the EVAP canister to maintain optimum stoichiometric air fuel mixture for the engine.

An EVAP purge valve malfunction could be caused by the following

1. Sticking EVAP purge valve.
2. EVAP purge valve blocked.
3. EVAP purge valve connector or harness wiring open or short circuit.
4. EVAP purge valve stuck open.

EVAP system includes a fuel pressure sensor and a Canister Vent Solenoid (CVS) valve. The system is capable of detecting holes in the fuel system down to 0.04" (1 mm).

ECM carries out test as follows

1. ECM closes the EVAP purge valve and CVS valve which closes off the fuel vapor storage system. The vent pressure will increase due to the fuel vapor pressure in the fuel tank. If the fuel vapor pressure increase is more than the acceptable limit, the test will abort because a false leak test response will result.
2. Next, the purge valve is opened during engine idle allowing the fuel tank pressure to decrease due to purge operation.
3. ECM will perform the leak test measurement. The pressure recorded from the tests determines the extent of a possible leak. If leak test measurement is greater than a preset limit on two consecutive tests, the ECM will set the appropriate DTC and illuminate the MIL. The leak test measurement is only carried out during engine idle with the vehicle stationary. When leak test is complete, ECM opens the CVS valve, returning the system to normal purge operation.

EVAP system includes a fuel tank pressure sensor and an EVAP Canister Vent Solenoid (CVS) valve, which is normally open. During EVAP system leak testing, ECM closes CVS valve and purge valve. ECM then monitors EVAP system pressure using fuel tank pressure sensor. If ECM detects a pressure decrease greater than a predetermined value, ECM will store a DTC. If EVAP CVS valve does not operate properly or a leak is detected, ECM will store a DTC.

CVS valve is mounted at the right side of the engine compartment. On Discovery Series II, battery voltage for CVS valve solenoid operation is supplied from Main relay and fuse No. 2 (15-amp) located in the engine compartment fuse/relay box. On Range Rover, battery voltage for CVS valve solenoid operation is supplied from Main relay and fuse No. 26 (20-amp) located in the engine compartment fuse/relay box. On all models, the ground connection is via the ECM which controls the CVS valve solenoid operation.

CVS valve is normally open, allowing any build up of pressure within EVAP system to escape, while keeping hydrocarbons in the EVAP canister. When the ECM is runs a fuel system test, the CVS valve is closed to seal the system. The ECM is then able to measure the pressure in the EVAP system using the fuel tank pressure sensor. ECM performs electrical integrity checks on the CVS valve to determine wiring or power supply malfunctions. The ECM can also detect a valve blockage if the signal from the fuel tank pressure sensor indicates a depressurizing fuel tank when the CVS valve should be open to the atmosphere.

Fuel tank pressure sensor measures fuel tank pressure allowing ECM to systematically check EVAP system for leaks. Fuel tank pressure sensor is located on top of fuel tank with fuel pump and fuel gauge sending unit. Fuel tank pressure sensor is a non-serviceable item. If pressure sensor replacement is necessary, the complete fuel tank pump and sending unit must be replaced.

A fuel tank pressure sensor failure will not be noticed by the driver, but if ECM detects a malfunction, it will store a DTC in diagnostic memory and the MIL will be illuminated.

Possible failure symptoms of the fuel tank pressure sensor are as follows

1. Fuel tank pressure sensor poor performance.
2. Fuel tank pressure sensor low range malfunction.
3. Fuel tank pressure sensor high range malfunction.

Fuel level sensor is located in fuel tank next to fuel pump. On Defender and Discovery, fuel level sensor is activated when fuel pump relay is energized. On Range Rover, fuel level sensor is activated through Body Electric Control Module (BECM). On all models, fuel level sensor signal is used for fuel gauge display. On Discovery with Advanced EVAP system, fuel level sensor signal can be used to disable fuel system and HO2S diagnostics.

The VSS is used, by the ECM, to control idle speed and over-run cut off. The ECM receives the signal through a hard wired connection direct from the Self Leveling and Anti-Lock Brake System (SLABS) ECU. On vehicles equipped with A/T, there are 2 vehicle speed signals received by the ECM. The second signal originates at the transmission output shaft speed sensor. It is sent to the ECM from the Electronic Automatic Transmission (EAT) ECU though the Controller Area Network (CAN). The ECM compares the vehicle speed signal generated by the SLABS ECU with that from the EAT ECU and information from the transfer case. This allows the ECM to consider vehicle speeds during low range gearing and compensate as necessary.

Vehicle speed signal generated by the SLABS ECU is a zero to battery voltage Pulse Width Modulated (PWM) signal. Signal pulses are generated 8000 times per mile, with a signal frequency that changes with road speed. At zero MPH the ECU outputs a 2 Hz reference signal for diagnostic purposes.

The VSS can fail in the following ways

1. An open circuit.
2. Short to battery voltage or ground.

In the event of a VSS failure, any of the following symptoms may be observed

1. MIL illuminated after 2 driving cycles.
2. SLABS/HDC warning lamp illuminated and audible warning.

Note. The IAC rotary valve must not be forced to move by mechanical means. The actuator can not be serviced; if defective, the entire IAC valve must be replaced as a unit.

IAC valve is used to maintain idle speed under all operating conditions. IAC valve uses 2 coils that use opposing PWM signals to control the opening and closing position of a rotary valve. If one of the PWM signal circuits fails, ECM closes down the remaining signal preventing the IAC valve from working at its maximum or minimum setting. If this should occur, the IAC valve automatically resumes a default idle position. In this condition, the engine idle speed is increased and maintained at 1200 RPM with no engine load. The cold start idle speed is held at 1200 RPM in neutral for approximately 20 seconds and ignition timing is retarded as a catalyst heating strategy. The cold start idle speed and the default idle speed position give the same engine speed. Although the idle speed is the same they must not be confused with each other as they are set separately by the ECM.

IAC valve diagnostic checks performed by the ECM are as follows

1. Opening coil output short circuit to ground.
2. Opening coil output short circuit to battery supply.
3. Opening coil output open circuit.
4. Closing coil output short circuit to ground.
5. Closing coil output short circuit to battery voltage.
6. Closing coil output open circuit.
7. If engine speed is 100 RPM less than the target speed, engine load is less than 2.5 and the measured air flow is more than 2.8 kg/s less than the expected air flow a DTC will be set as a blocked IAC valve with a low RPM error.
8. If engine speed is more than 180 RPM greater than the target speed and the measured air flow is more than 2.8 kg/s greater than the expected air flow for a DTC will be set as a blocked IAC valve with a high RPM error.

IAC valve can fail or supply an incorrect signal in the following ways

1. Actuator malfunction.
2. Rotary valve seized.
3. Wiring harness or connector fault.
4. Intake air system air leak.
5. Blocked, restricted or crimped actuator port or hoses.

When ignition is turned to ON position battery voltage is applied to charging system fault indicator. Indicator will go out when generator begins to operate.

Controller Area Network (CAN) system is a high speed serial interface between the ECM and the Electronic Automatic Transmission (EAT) ECU. The CAN system uses a data bus to transmit information messages between ECM and EAT ECU. Because there are only two components in this CAN system, one will transmit information messages and the other will receive information messages, and vice-versa.

The CAN system uses a twisted pair of wires to form the data bus to reduce electrical interference. The information messages are structured so that each of the receivers (ECM or EAT ECU) is able to interpret and react to the messages sent.

CAN system is used by the EAT ECU and ECM for transmission of the following information

1. Gearshift torque control information.
2. Gear selected and gear change information.
3. EAT OBD information and MIL illumination request.
4. Vehicle speed signal.
5. Engine torque and speed.
6. Engine coolant temperature.
7. Intake air temperature.
8. Altitude adaptation factor.
9. Throttle angle and/or pedal position.

If there is a Controller Area Network (CAN) malfunction the following DTCs may be set

1. If DTC P0601 is set, there is an internal ECM memory check sum error.
2. If DTC P0603 is set, there is an internal ECM keep alive memory Random Access Memory (RAM) error.
3. If DTC P0604 is set, there is an internal ECM RAM error.
4. If DTC P0606 is set, there is a ECM processor malfunction.

When ignition is turned to ON position, ECM carries out a Amber SERVICE ENGINE SOON/MIL self-test. As a bulb check, MIL will illuminate for 3 seconds when ignition switch is turned to ON position and should go out if no DTCs are detected. If a DTC is detected the MIL will be will go out for one second before illuminating again to indicate a DTC exists.

ECM uses CKP sensor signal to determine engine speed. ECM shares the engine speed information with the Electronic Automatic Transmission (EAT) ECU, tachometer located in instrument cluster, Body Electrical Control Module (BECM) by transmitting the data via the CAN link. On Discovery Series II, engine speed output signal is scaled down to 2 pulses per crankshaft revolution and sent to the tachometer. On Range Rover, engine speed output signal is scaled down to 4 pulses per crankshaft revolution and sent to the tachometer.

The fuel pump relay is a 4-pin normally open relay located in the engine compartment fuse/relay box. Fuel pump relay controls the fuel pump operation, regulating fuel supply to fuel injectors. When ignition switch is turned on and the engine is cranked, the ECM activates the fuel pump relay, allowing fuel system to be pressurized to 52 psi (3.6 kPa). The ECM then deactivates the relay until the engine has started and fuel pressure decreases. If the fuel pump operates, but the fuel pressure is out of limits, adaptive fuel faults will be stored.

If there is a fuel pump relay failure any of the following symptoms may be observed

1. The engine stalls or will not start.
2. There is no fuel pressure at the fuel injectors.

SAI control valves are located on brackets at each side of the engine. SAI air injection supply pipes connect to a large port on the side of each SAI control valve via a short rubber connection hose. A small vacuum port is located on each SAI control valve opposite the air injection supply port. Vacuum supply to each vacuum operated SAI control valve is through small nylon hoses from the SAI vacuum solenoid valve. An intermediate connector is included in the vacuum hose to split the vacuum applied to each vacuum operated valve, so that both valves open and close simultaneously.

When vacuum is applied to SAI control valves, the valve opens to allow the pressurized air from the SAI pump through to the exhaust manifolds. The injection air is output from each SAI control valve through a port in the bottom of each unit. A metal pipe connects the output port of each SAI control valve and each exhaust manifold via an intermediate "T" fitting. The "T" fitting splits the pressurized air delivered to the two center exhaust ports on each cylinder head. The pipes between the "T" fitting and the exhaust manifold are enclosed in thermal sleeving to protect the surrounding components from the heat of the exhaust gases. When the SAI vacuum solenoid valve is de-energized, the vacuum supply line opens to atmosphere, causing the vacuum operated valves to close automatically.

Request for A/C operation is signaled to Heating and Ventilation Air Conditioning (HVAC) control unit and ECM when A/C control panel switch is pressed, completing a ground path. Battery voltage to A/C control panel switch is supplied via ECM 40-pin connector C0637 terminal No. 38 (Purple/White wire on Discovery Series II; Yellow/Black wire on Range Rover). When A/C operation request is received, A/C compressor clutch will be engaged based on other operating requirements. If there is an A/C request failure, the A/C system will not work even if all other requirements are met.

The A/C compressor clutch relay is a 4-pin normally open relay located in the engine compartment fuse box. When the ECM grounds A/C clutch relay coil the switching contacts close o allow the relay contacts to close and the A/C clutch to receive battery voltage. When the ECM opens the ground path, the clutch relay will be de-energized and shut down A/C compressor clutch. Battery voltage to A/C clutch relay is supplied via fuse No. 6 (10-amp) located in the engine compartment fuse/relay box. Battery voltage to A/C clutch relay coil is supplied from the main relay, also located in the engine compartment fuse/relay box. A/C clutch relay coil ground is supplied via ECM 40-pin connector terminal No. 29 (Black/Gray wire on Discovery Series II; Black/Green wire on Range Rover). When the relay is energized the output from the switching contacts goes directly to the A/C compressor clutch. If there is an A/C clutch relay failure, the A/C system will not work even if all other requirements are met.

When the vehicle travels across rough terrain, or on rough roads the ECM could falsely interpret suspension vibrations as a misfire and invoke engine misfire protocols and/or set a false DTC. The Self-Leveling and Anti-Lock Brake System (SLABS) ECU sends a rough road PWM signal to the ECM. Based on this rough road PWM signal, the ECM can suspend misfire detection for as long as the vehicle is travelling on a rough road.

Rough road signal input is measured at ECM 40-pin connector C0637 terminal No. 34 (Red/Green wire on Discovery Series II; Yellow/Pink wire on Range Rover). The SLABS ECU rough road PWM signal varies in accordance with changing road conditions. The rough road PWM signal operates at a frequency of 2.10-2.56 Hz. ECM rough road control is based on specific changes to the PWM signal. If there is a rough road PWM signal failure the Hill Descent Control/Anti-Lock Braking System (HDC/ABS) warning light may be illuminated.

The ECM transmits throttle angle, engine torque, engine identification, and transmission type data to the SLABS ECU to support the Hill Descent Control (HDC) system. The data is transmitted via a 0-12 volt PWM signal at a frequency of 179.27 Hz.

HDC signal output is from ECM 52-pin connector C0636 terminal No. 29 (Gray/Purple wire). The ECM generates a PWM signal that varies in pulse width in accordance with changing throttle angle or engine torque. The throttle angle data is transmitted on pulses 1, 3, 5 and 37. The engine torque data is transmitted on pulses 2, 4, 6 and 38. The type of engine and transmission information is transmitted on pulse 39. A synchronizing pulse is transmitted after every 39th pulse.

ECM and Body Control Unit (BCU) security system comprise the immobilization system. The ECM and BCU combine to prevent the engine from operating unless the appropriate security criteria are met. The ECM and BCU are a matched pair, if either one is replaced for any reason, the system will not operate unless the replaced unit is correctly synchronized to its original specification. A Land Rover TestBook must be used to reconfigure and synchronize the immobilization system. The ECM operates the vehicle immobilization system in a NEW, SECURE or NO CODE state.

When the ECM operating in the NEW state, a Land Rover TestBook is required to instruct the ECM to learn a new BCU code. If the ECM is a NEW replacement direct from the supplier, it will not operate the vehicle and will store a new ECM DTC when it is installed. This DTC must be cleared after instructing the ECM to learn the BCU code using TestBook.

When the ECM is operating 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 has an ECM with a valid code, the engine will start and the MIL will go out. 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 determined using Land Rover TestBook. The immobilization serial "W" link signal input is at ECM 40-pin connector C0637 terminal No. 33 (Light Green/Gray wire).

On Range Rover, the ECM is located at the left corner of the engine compartment inside an "E" box. The ECM "E" box is equipped with a cooling fan that provides cooler cabin air into the "E" box to provide a cooler environment for the Bosch Motronic 5.2.1 ECM. "E" box cooling fan operation is controlled by the ECM. The operating temperature of the ECM is monitored by an internal temperature sensor which it uses to determine when "E" box cooling fan operation is necessary.

When an OBD relevant error is detected within the transfer case Electronic Control Unit (ECU), a MIL illumination request is sent to ECM. If transfer case cannot move into high range, an incorrect transfer motor position is detected or a vehicle speed sensor malfunction is detected and the ECM will store a DTC. MIL will illuminate if malfunctions are detected during 2 drive cycles. Each time the ignition is turned on (power-up) the ECM checks the signal line. The transfer case ECU is located under the left front seat and has one 36-pin harness connector.