Engine Controls - System & Component Testing Land Rover Discovery L318

INTRODUCTION

Before testing separate components or systems, follow proper workflow. See DIAGNOSTIC PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. If no Diagnostic Trouble Codes (DTC) are present and a no-start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If no DTCs are present and a driveability condition exists, proceed to appropriate TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

Discovery is equipped with Generic Engine Management System (GEMS). 1999-2000 Range Rover and Discovery Series II are equipped with Bosch Motronic 5.2.1 engine management system.

Note. Testing individual components does not isolate short or open circuits. Perform all resistance and voltage tests using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate shorted or open wiring harness.

Scheme 19

Scheme 20

Scheme 21

Scheme 22

Ground Circuits (Discovery)

1. Using a backprobe set, check for continuity in Black wires between ground connection and ECM Black 18-pin connector terminals No. 5, 9 and 10, individually. (Scheme 23) See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If continuity exists, go to next step. If continuity does not exist, repair open in suspect Black wire.
2. Start engine and allow to idle. Using a backprobe set, measure voltage between ground and ECM Black 18-pin connector terminals No. 5, 9 and 10. Voltage should be less than one volt. If voltage is greater than one volt, check for an open, corrosion or loose ground connection. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).

Power Circuits (Discovery)

Turn ignition on. Using a backprobe set, measure voltage between ground and ECM Black 18-pin connector terminal No. 8 (White/Green wire). See WIRING DIAGRAMS . If battery voltage does not exist, check fuse No. 3 (20-amp), located in satellite fuse box No. 1. If fuse is okay, check for an open in suspect circuit between fuse box and ECM. If fuse is not okay, repair short in suspect circuit and replace fuse. See WIRING DIAGRAMS .

Scheme 23

Ground Circuits (Discovery Series II & Range Rover)

1. Using a backprobe set, check for continuity in Black wires between ground and ECM Black 9-pin connector C0634 terminals No. 4, 5, and 6, Black 52-pin connector C0636 terminal No. 17 and Gray 9-pin connector C0638 terminal No. 5, individually. (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). On Discovery Series II, ground connection is located at right rear side of engine compartment. On Range Rover, ground connection is located at right side of engine compartment, near the horn. If continuity exists, go to next step. If continuity does not exist, repair open in suspect Black wire.
2. Start engine and allow to idle. Using a backprobe set, measure voltage between ground and ECM Black 9-pin connector C0634 terminals No. 4, 5, and 6, Black 52-pin connector C0636 terminal No. 17 and Gray 9-pin connector C0638 terminal No. 5, individually. Voltage should be less than one volt. If voltage is greater than one volt, check for an open, corrosion or loose ground connection. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).

Power Circuits (Discovery Series II)

1. Turn ignition off. Using a backprobe set, check for voltage between ground and ECM Black 9-pin connector C0634 terminal No. 7 (Purple/Yellow wire). If battery voltage is present, go to next step. If battery voltage is not present, check for open or short in Purple/Yellow wire between ECM and fuse No. 12 (20-amp) located in engine compartment fuse/relay box. (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). Perform repairs as necessary.
2. Turn ignition off. Using a backprobe set, measure voltage between ground and ECM Black 24-pin connector C0635 terminal No. 23 (Blue/Red wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage does not exist, ensure inertia switch is closed. If necessary, reset inertia switch and recheck for voltage. If inertia switch is closed, check circuit between ECM, main relay, inertia switch and fuse No. 13 (15-amp), located in engine compartment fuse/relay box. Perform repairs as necessary.

Power Circuits (Range Rover)

Turn ignition off. Using a backprobe set, check for voltage between ground and ECM Black 9-pin connector C0634 terminal No. 7 (Purple/Yellow wire). If battery voltage is present, go to next step. (Scheme 24)and (Scheme 25). See WIRING DIAGRAMS. If battery voltage is not present, check for open or short in Purple/Yellow wire between ECM and fuse No. 44 (30-amp) located in engine compartment fuse/relay box. Perform repairs as necessary.

Scheme 24

Scheme 25

CAMSHAFT POSITION (CMP) SENSOR & CRANKSHAFT POSITION (CKP) SENSOR SYNCHRONIZATION

1. CKP sensor is located on the left side of flywheel housing. CMP sensor is located on left front of engine.
2. Compare CKP sensor wave pattern with known-good pattern. Check wave pattern for bent teeth on reluctor ring and regularity. See DTC P0335 & P0336: CRANKSHAFT POSITION (CKP) SENSOR MALFUNCTION testing in appropriate SELF-DIAGNOSTICS article. If wave pattern is okay, go to next step. If CKP wave pattern is okay and engine misfire DTCs are set, see DTC P0300-P0308: MISFIRE DETECTED IN ONE OR MORE CYLINDERS testing in appropriate SELF-DIAGNOSTICS article. If wave pattern is not okay, go to «CRANKSHAFT POSITION (CKP) SENSOR»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__camshaft-position-cmp-sensor-circuit) .
3. Compare CMP sensor wave pattern with known-good wave pattern. See DTC P0340: CAMSHAFT POSITION (CMP) SENSOR MALFUNCTION in appropriate SELF-DIAGNOSTICS article. If wave pattern is okay, go to next step. If wave pattern is not okay, go to «CRANKSHAFT POSITION (CKP) SENSOR»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__camshaft-position-cmp-sensor-circuit) .
4. Compare synchronization of CKP sensor and CMP sensor wave patterns with known-good patterns. See DTC P0340: CAMSHAFT POSITION (CMP) SENSOR MALFUNCTION in appropriate SELF-DIAGNOSTICS article. If wave patterns are synchronized, both sensors are okay. If wave patterns are not synchronized, go to «CRANKSHAFT POSITION (CKP) SENSOR»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__camshaft-position-cmp-sensor-circuit) .

CAMSHAFT POSITION (CMP) SENSOR CIRCUIT

Note. It is physically possible to interchange the camshaft sprocket installed on vehicles equipped with GEMS ignition system and vehicles equipped with Bosch Motronic 5.2.1 ignition system. However, because the GEMS and Motronic systems are incompatible, an incorrect camshaft signal will be received by the ECM and DTC P0340 will set.

1. Check for CMP sensor output wave pattern. If there is no sensor output wave pattern, go to step 4 . If there is an output wave pattern, go to next step.
2. Compare wave pattern with known-good wave pattern. See DTC P0340: CAMSHAFT POSITION (CMP) SENSOR MALFUNCTION in appropriate SELF-DIAGNOSTICS article. If wave pattern is okay, go to next step. If wave pattern is not okay, ensure correct cam reluctor ring and cam shaft are installed in engine. It is possible for an incorrect camshaft to be installed in engine. If camshaft and reluctor ring are correct, ensure CMP sensor is correctly installed. Repair as necessary and recheck wave pattern.
3. Compare synchronization of CKP sensor and CMP sensor wave patterns with known-good patterns. See DTC P0340: CAMSHAFT POSITION (CMP) SENSOR MALFUNCTION in appropriate SELF-DIAGNOSTICS article. If wave patterns are synchronized, both sensors are okay. If wave patterns are not synchronized, cam timing is incorrect. Repair as necessary and recheck wave pattern.
4. Remove CMP sensor. Without touching engine block, wave CMP sensor close enough to generate an output signal. If there is still no output signal from sensor, go to next step. If there is an output wave pattern, repeat step 2 . If step 2) has been repeated one time already, substitute a known-good ECM and recheck system. If symptom or indication goes away, replace original ECM.
5. Check for poor connections or loose wires between CMP sensor and ECM. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . Repair as necessary and recheck. If no problems are found with wires or connectors, replace CMP sensor and recheck. Ensure wave pattern is okay.

CRANKSHAFT POSITION (CKP) SENSOR CIRCUIT

1. Check CKP sensor installation. Ensure sensor is secure, and that the heat shield and connector are correctly installed. If incorrect spacer is installed sensor will have either a weak signal or hit the reluctor ring. Remove CKP sensor and ensure tip is not bent or damaged. Repair or replace components as necessary.
2. Remove "D" plate from transmission bell housing and inspect condition of reluctor ring. Rotate engine and check runout of reluctor ring. If any teeth are bent or reluctor ring does not run true, replace reluctor ring and flywheel. After replacing reluctor ring check CKP sensor wave pattern. See DTC P0335 & P0336: CRANKSHAFT POSITION (CKP) SENSOR MALFUNCTION testing in appropriate SELF-DIAGNOSTICS article. If wave pattern is okay, repair is complete. If wave pattern is not okay, go to next step.
3. Check for poor connections or loose wires between CKP sensor and ECM. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . Repair as necessary and recheck wave pattern. If wave pattern is okay, repair is complete. If wave pattern is not okay, go to next step.
4. Measure CKP sensor resistance between sensor terminals. Nominal sensor resistance is 1235-1365 ohms. If sensor resistance is not 1000-1600 ohms, replace CKP sensor and recheck CKP sensor wave pattern.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

Turn ignition off. Disconnect ECT sensor connector. Drain small amount of coolant. Remove ECT sensor from vehicle and measure resistance at various temperatures. Replace ECT sensor if not within specification. See ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE table.

ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE

ENGINE FUEL TEMPERATURE (EFT) SENSOR

EFT sensor is located on left side of engine, mounted to fuel rail. Turn ignition off and disconnect sensor connector. Remove EFT sensor from vehicle and measure resistance at various temperatures. Replace sensor if not within specification. See ENGINE FUEL TEMPERATURE SENSOR RESISTANCE table.

ENGINE FUEL TEMPERATURE SENSOR RESISTANCE

HEATED OXYGEN SENSOR (HO2S) CIRCUIT

There are 2 Primary Heated Oxygen Sensors (HO2S-1) located in front of each catalytic convertor. There are 2 Secondary Heated Oxygen Sensors (HO2S-2) located after each catalytic convertor. Start engine and bring to normal operating temperature. Compare wave patterns with known-good wave patterns. See P0150-P0153, P0156-P159, P0171-P0172, P0174-P0175, P1137-P1139, P1157-P1159, P1171-P1172 & P1185-P1196: HO2S CIRCUIT MALFUNCTION testing in appropriate SELF-DIAGNOSTICS article. See HEATED OXYGEN SENSOR VOLTAGE and HEATED OXYGEN SENSOR HEATER RESISTANCE tables.

HEATED OXYGEN SENSOR VOLTAGE

HEATED OXYGEN SENSOR HEATER RESISTANCE

INTAKE AIR TEMPERATURE (IAT) SENSOR

Intake air temperature sensor is located on air cleaner housing. Turn ignition off and disconnect sensor connector. Remove sensor from vehicle and measure resistance at various temperatures. Replace sensor if not within specification. See INTAKE AIR TEMPERATURE SENSOR RESISTANCE table.

INTAKE AIR TEMPERATURE SENSOR RESISTANCE

KNOCK SENSOR (KS)

There are 2 knock sensors located on either side of engine block. One mounted between cylinders No. 3 and 5, the other mounted between cylinders No. 2 and 4. Check for continuity between KS terminal and KS body. If continuity exists, replace KS.

MASS AIRFLOW SENSOR (MAF) CIRCUIT

1. In heavily polluted atmospheres MAF sensor may become contaminated causing incorrect voltage outputs. An air intake system that is restricted, has air leaks or missing components will cause incorrect voltage outputs. Turn ignition on. Measure voltage between ground and MAF sensor 3-pin connector terminal No. 1 (Brown/Orange wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If battery voltage does not exist, go to next step. If battery voltage exists, go to step 3 .
2. Measure voltage between ground and ECM Black 18-pin connector terminal No. 7 (Brown/Orange wire). If battery voltage does not exist, repair open or short in Brown/Orange wire between ECM and relay. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If battery voltage exists, repair open in Brown/Orange wire between MAF sensor and relay. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) .
3. Start engine and allow to idle. Backprobe MAF sensor 3-pin connector. Measure output voltage between sensor output terminal No. 2 (Blue/Green wire) and sensor ground terminal No. 3 (Red/Black wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . Voltage output should increase as air flow increases. See «MASS AIRFLOW SENSOR OUTPUT VOLTAGE»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing) table.

MASS AIRFLOW SENSOR OUTPUT VOLTAGE

Scheme 26

PARK/NEUTRAL SWITCH

See IDLE CONTROL SYSTEM (GEMS) .

THROTTLE POSITION (TP) SENSOR

Note. TP sensor and fuel tank pressure sensor share a 5.0 volt reference voltage. A fuel tank pressure sensor failure that causes a short circuit will affect TP sensor output and set a TP sensor DTC.

Check TP sensor output voltage. See THROTTLE POSITION SENSOR SIGNAL VOLTAGE table. TP sensor output voltage should change smoothly as throttle position changes. Turn ignition off and disconnect TP sensor 3-pin connector. TP sensor resistance measured between terminals No. 1 and No. 3 should be 3200-4800 ohms. Replace TP sensor if output voltage or resistance is not as specified.

THROTTLE POSITION SENSOR VOLTAGE

VEHICLE SPEED SENSOR

See DTC P0500: VEHICLE SPEED SENSOR (VSS) SIGNAL OUT OF RANGE in appropriate SELF-DIAGNOSTICS article.

Note. It is physically possible to interchange the camshaft sprocket installed on vehicles equipped with GEMS ignition system and vehicles equipped with Bosch Motronic 5.2.1 ignition system. However, because the GEMS and Motronic systems are incompatible, an incorrect camshaft signal will be received by the ECM and DTC P0340 will set.

1. CMP sensor is located at the front of the engine block, above and behind the crankshaft pulley. CMP sensor is a magnetic switch used for switching battery voltage ON and OFF as slots in the camshaft sprocket pass by the sensor. This results in a 0.0-12.0 volt output signal sent as a square wave pattern to ECM 52-pin connector C0636 terminal No. 20 (Gray/Blue wire). (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).
2. Check for a CMP sensor wave pattern. If there is no wave pattern, go to next step. If wave pattern is not as specified, ensure correct cam sprocket is installed. Ensure that CMP sensor air gap between sensor and the side of the camshaft sprocket is less than 0.08" (2.0 mm) and that "O" ring is not damaged. Perform repairs as necessary.
3. Turn ignition off. Remove CMP sensor. Turn ignition on. Without touching engine block, wave CMP sensor close enough to generate an output signal. If no signal is generated, go to next step. If a signal is generated, ensure CMP sensor is correctly installed (install a NEW "O" ring) and check for excessive camshaft sprocket runout tolerance, excessive camshaft end-play, misaligned camshaft and crankshaft, incorrect speed signal correlation with CKP sensor signal or a magnetized camshaft sprocket.
4. Turn ignition off. Check for continuity in Black wire between CMP sensor 3-pin connector terminal No. 1 and ECM 52-pin connector C0636 terminal No. 17. If continuity exists, go to next step. If continuity does not exist, repair open in Black wire.
5. Turn ignition off. Check for continuity in Black wire between ground and CMP sensor 3-pin connector terminal No. 1 and ECM 52-pin connector C0636 terminal No. 17. If continuity exists, go to next step. If continuity does not exist, repair open in Black wire.
6. Turn ignition off. Check for continuity in Gray/Blue wire between CMP sensor 3-pin connector terminal No. 2 and ECM 52-pin connector C0636 terminal No. 20. If continuity exists, go to next step. If continuity does not exist, repair open in Gray/Blue wire.
7. Turn ignition on. Measure voltage between ground and CMP sensor 3-pin connector terminal No. 3 (Brown/Pink wire). If battery voltage is present, go to next step. On Discovery Series II, if battery voltage is not present, check fuse No. 2 (15-amp) located in engine compartment fuse/relay box. On Range Rover, if battery voltage is not present, check fuse No. 26 (20-amp) located in engine compartment fuse/relay box. On all models, if fuse is okay, check Brown/Pink wire. Perform repairs as necessary.

1. Check CKP sensor installation. Ensure sensor is secure, and that the heat shield and connector are correctly installed. If incorrect spacer is installed sensor will have either a weak signal or hit the reluctor ring. Remove CKP sensor and ensure tip is not bent or damaged. Repair or replace components as necessary.
2. Remove inspection plate from transmission bell housing and inspect condition of reluctor ring teeth. Rotate engine and check reluctor ring runout. If any teeth are bent or missing, or reluctor ring does not run true, replace reluctor ring and/or flywheel. After replacing reluctor ring check CKP sensor wave pattern. CKP sensor signal is a 0-300 mV AC that changes as engine speed increases and decreases. If wave pattern is okay, repair is complete. If wave pattern is not okay, go to next step.
3. Turn ignition off. Disconnect CKP sensor 3-pin connector and ECM 52-pin connector C0636. (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). Check for continuity between CKP sensor connector terminal No. 3 (Black wire) and ECM 52-pin connector C0636 terminal No. 45. If continuity exists, go to next step. If continuity does not exist, repair open in Black wire.
4. Turn ignition off. Check for continuity between ground and ECM 52-pin connector C0636 terminal No. 45 (Black wire). If continuity does not exist, go to next step. If continuity exists, repair short to ground in CKP sensor shield circuit. If sensor shield is not properly grounded a false or interrupted signal may be result.
5. Turn ignition off. Check for continuity between CKP sensor connector terminal No. 2 (Pink/Black wire) and ECM 52-pin connector C0636 terminal No. 46 (Pink/Black wire). If continuity exists, go to next step. If continuity does not exist, repair open or short in Pink/Black wire.
6. Turn ignition off. Check for continuity between CKP sensor connector terminal No. 1 (Black/Yellow wire) and ECM 52-pin connector C0636 terminal No. 32 (Black/Yellow wire). If continuity exists, go to next step. If continuity does not exist, repair open or short in Black/Yellow wire.
7. Turn ignition off. Reconnect ECM 52-pin connector C0636 and CKP sensor 3-pin connector. Turn ignition to START position. Check for a 0-300 mV AC signal at ECM 52-pin connector C0636 terminal No. 32 (Black/Yellow wire) as engine turns over. Voltage should vary and increase as engine speed increases with a peak voltage of approximately 300 mV. If signal voltage is not as specified, replace CKP sensor and recheck. If voltage is as specified, repair is complete.

Turn ignition off. Disconnect ECT sensor connector. Drain small amount of coolant. Remove ECT sensor from vehicle and measure resistance at various temperatures. Replace ECT sensor if not within specification. (Scheme 27)

Scheme 27

HEATED OXYGEN SENSOR (HO2S)

There are 2 primary Heated Oxygen Sensors (HO2S) located in front of each catalytic convertor. There are 2 secondary HO2S located after each catalytic convertor. Start engine an operate at normal operating temperature. Replace HO2S if output voltage is not as specified. See HEATED OXYGEN SENSOR (HO2S) OUTPUT VOLTAGE (BOSCH) table.

HEATED OXYGEN SENSOR (HO2S) OUTPUT VOLTAGE (BOSCH)

MASS AIRFLOW/INTAKE AIR TEMPERATURE (MAF/IAT) SENSOR CIRCUIT

1. Turn ignition off. Disconnect MAF/IAT sensor unit 5-pin connector. Turn ignition on and measure voltage between ground and connector terminal No. 2 (Brown/Pink wire). See WIRING DIAGRAMS article. If battery voltage is present, go to next step. If battery voltage is not present, check for an open or short in Brown/Pink wire between MAF/IAT sensor and fuse (No. 2, 15-amp on Discovery Series II or No. 26, 20-amp on Range Rover) located in engine compartment fuse/relay box. Perform repairs as necessary.
2. Turn ignition on and measure voltage between ground and MAF/IAT sensor connector terminal No. 4 (Red wire). If 5.0 volts is present, go to next step. If 5.0 volts is not present, check for an open or short in Red wire between MAF/IAT sensor and ECM 52-pin connector C0636 terminal No. 7. Perform repairs as necessary.
3. Turn ignition off. Check for continuity between ground and MAF/IAT sensor connector terminal No. 3 (Red/Black wire). If continuity exists, go to next step. If continuity does not exist, check for an open or short in Red/Black wire between MAF/IAT sensor and ECM 52-pin connector C0636 terminal No. 9. Perform repairs as necessary.
4. Turn ignition off and connect MAF/IAT sensor 5-pin connector. Start engine and allow to idle at normal operating temperature. Backprobe MAF/IAT sensor 5-pin connector terminal No. 1 (Gray/Light Green wire) and measure sensor output signal voltage. Output signal voltage should be approximately 0.0-5.0 volts and increase as engine speed and airflow increase. (Scheme 28) If voltage is as specified, go to next step. If voltage is not as specified, replace MAF sensor and retest.
5. Start engine and allow to idle at normal operating temperature. Backprobe ECM 52-pin connector C0636 terminal No. 34 (Gray/Light Green wire) measure sensor output signal voltage. Output signal voltage should be approximately 0.0-5.0 volts and increase as engine speed and airflow increases. (Scheme 28) If voltage is as specified, go to next step. If voltage is not as specified, check Gray/Light Green wire for an open or short between MAF/IAT sensor and ECM. Check for poor connections, loose terminals, and wires. Perform repairs as necessary.
6. Turn ignition off and connect MAF/IAT sensor 5-pin connector. Start engine and allow to idle at normal operating temperature. Backprobe MAF/IAT sensor 5-pin connector terminal No. 5 (Blue/Green wire) and measure sensor output signal voltage. Output signal voltage should be approximately 0.0-5.0 volts and increase as engine speed and airflow increase. (Scheme 29)table. If voltage is as specified, go to next step. If voltage is not as specified, replace MAF sensor and retest.
7. Start engine and allow to idle at normal operating temperature. Backprobe ECM 52-pin connector C0636 terminal No. 23 (Blue/Green wire) measure sensor output signal voltage. Output signal voltage should be approximately 0.0-5.0 volts and increase as engine speed and airflow increases. (Scheme 29) If voltage is not as specified, check Blue/Green wire for an open or short between MAF/IAT sensor and ECM. Check for poor connections, loose terminals, and wires. Perform repairs as necessary.

Scheme 28

Scheme 29

Ensure KS mounting bolt is tightened to 16 ft. lbs. (22 N.m). Check for poor connections, loose terminals, and open or shorted wires. See WIRING DIAGRAMS .

Note. Because ECM is able to determine the closed throttle position, the TP sensor does not need to be adjusted when replaced.

1. Check for poor connections, loose terminals, and open or shorted wires. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If no problems are found, go to next step. Perform repairs as necessary.
2. Turn ignition on. Backprobe between ECM 52-pin connector C0636 terminals No. 24 (Yellow/Light Green wire) and No. 25 (Red/Black wire). Measure voltage while moving throttle valve between fully closed (idle) and fully open (wide open) positions. See «THROTTLE POSITION SENSOR SIGNAL VOLTAGE»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing) table. If voltage is as specified and changes smoothly, test is complete. If voltage is not as specified, replace TP sensor.

THROTTLE POSITION SENSOR SIGNAL VOLTAGE

CANISTER PURGE SOLENOID (DISCOVERY)

Measure resistance between canister purge solenoid terminals. See WIRING DIAGRAMS . Resistance should be approximately 22-40 ohms. Replace canister purge solenoid if resistance is not as specified.

Discovery

Fuel injector solenoid resistance should by approximately 15.7-16.7 ohms at 68°F (20°C).

Discovery Series II & Range Rover

Fuel injector solenoid `resistance should be approximately 13.8-15.2 ohms at 68°F (20°C).

1. Fuel pump relay is an integral component of the multifunction relay unit, which is located in right rear of engine compartment. Disconnect connectors at multifunction relay unit. Check continuity with ohmmeter positive probe connected to multifunction relay unit 6-pin Black connector C1030 terminal No. 2 and negative probe connected to multifunction relay unit 6-pin Black connector C1030 terminal No. 1. (Scheme 31) Continuity should exist. If continuity is as specified, go to next step. If continuity is not as specified, replace multifunction relay unit.
2. Reverse polarity of the ohmmeter. Continuity should not exist. If continuity is as specified, go to next step. If continuity is not as specified, replace multifunction relay unit.
3. Check continuity between multifunction relay unit 9-pin Black connector C1029 terminals No. 7 and 4. (Scheme 30) Continuity should not exist. If continuity is as specified, go to next step. If continuity is not as specified, replace multifunction relay unit.
4. Apply battery voltage to multifunction relay unit 6-pin Black connector C1030 terminal No. 2 and ground multifunction relay unit 6-pin Black connector C1030 terminal No. 1. Check continuity between multifunction relay unit 9-pin Black connector C1029 terminals No. 7 and 4. Continuity should exist. If continuity is as specified, fuel pump relay is okay. If continuity is not as specified, replace multifunction relay unit.

Scheme 30

Scheme 31

1. Fuel pump relay is an integral component of the multifunction relay unit, which is located in right rear of engine compartment. Before checking fuel pump relay, check inertia fuel shut-off switch located on engine compartment firewall. Check for continuity between inertia fuel shut-off switch White/Purple wire terminals. If continuity exists, go to next step. If continuity does not exist, depress inertia fuel shut-off switch plunger to reset switch. If continuity still does not exist, replace inertia fuel shut-off switch.
2. Turn ignition off. Disconnect ECM Black 36-pin and 18-pin connectors. Turn ignition on. Measure voltage between ground and multifunction relay unit 6-pin connector terminal No. 2 (White/Green wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, go to step 4. If battery voltage does not exist, go to next step.
3. If battery voltage does not exist, check fuse No. 3 (20-amp), located in satellite fuse/relay box No. 1 behind fascia, left of steering column. If fuse is okay, repair open in White/Green wire. If fuse is not okay, repair short in White/Green wire and replace fuse. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).
4. Using a backprobe set, measure voltage between ground and ECM Black 18-pin connector terminal No. 8 (White/Green wire). (Scheme 23) See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, go to next step. If battery voltage does not exist, repair open in White/Green wire.
5. Ensure ignition is on. Measure voltage between ground and multifunction relay unit 8-pin connector terminal No. 7 (Purple/White wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, go to next step. If battery voltage does not exist, check fuse No. 6 (15-amp). If fuse is not okay, repair short in Purple/White wire and replace fuse. If fuse is okay, check for an open in Purple/White wire. Repair as necessary. If Purple/White wire is okay, repair open or short in power supply circuit between battery and fuse No. 6. See POWER DISTRIBUTION in «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).
6. Turn ignition off. Using a fused jumper wire and backprobe set, connect ECM Black 36-pin connector terminal No. 24 (Blue/Purple wire) to ground. (Scheme 26) See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). Turn ignition on. Check fuel pump operation. If fuel pump is not operating, go to next step. If fuel pump is operating, substitute a known-good ECM and recheck for original symptom or indication. If symptom or indication goes away, replace original ECM.
7. Measure voltage between ground and multifunction relay unit 8-pin connector terminal No. 4 (White/Purple wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, repair open in circuit between multifunction relay unit, inertia fuel shut-off switch and fuel pump. If battery voltage does not exist, replace fuel pump relay and recheck.

Discovery Series II

1. Ensure main relay is operating properly. See «Main Relay (Discovery Series II)»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing) . Remove fuel pump relay. Turn ignition on. Measure voltage between ground and fuel pump relay connector terminal No. 85. If battery voltage is present, go to next step. If battery voltage is not present, check for continuity between fuel pump relay connector terminal No. 85 and main relay connector terminal No. 87. If continuity does not exist, repair or replace engine compartment fuse/relay box.
2. Turn ignition off. Check for continuity between fuel pump relay connector terminal No. 86 and ECM 24-pin connector C0635 terminal No. 18 (Blue/Purple wire). If continuity exists, go to next step. If continuity does not exist, repair open in Blue/Purple wire. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) .
3. Turn ignition off. Measure voltage between ground and fuel pump relay connector terminal No. 30. If battery voltage is present, go to next step. If battery voltage is not present, check fuse No. 10 (30-amp). If fuse is blown, go to next step. If fuse is okay, check for continuity in fuse/relay box circuit between fuel pump relay connector terminal No. 30 and battery voltage supply Red wire connection. If continuity does not exist, repair or replace engine compartment fuse/relay box.
4. If fuse No. 10 (30-amp) is blown, check for a short in White/Purple wire between fuel pump relay in engine compartment fuse/relay box and fuel pump connector terminal No. 1. Perform repairs as necessary. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) .
5. Check for continuity between fuel pump relay terminals No. 1 and 2. If continuity exists, go to next step. If continuity does not exist, replace fuel pump relay.
6. Check for continuity between fuel pump relay terminals No. 3 and 5. If continuity does not exist, go to next step. If continuity exists, replace fuel pump relay.
7. Using a fused jumper wire, connect battery voltage to fuel pump relay terminal No. 1. Using another jumper wire, connect fuel pump relay terminal No. 2 to ground. When fuel pump relay is energized, check for continuity between fuel pump relay terminals No. 3 and 5. If continuity does not exist, replace fuel pump relay.

Range Rover

1. Fuel pump relay is in engine compartment fuse/relay box, which is located on right side of engine compartment. Before checking fuel pump relay, check inertia fuel shut-off switch located on engine compartment firewall. Check for continuity between inertia fuel shut-off switch terminals No. 1 (White/Orange wire) and No. 3 (White/Blue wire). If continuity exists, go to next step. If continuity does not exist, depress inertia fuel shut-off switch plunger to reset switch. If continuity still does not exist, replace inertia fuel shut-off switch.
2. Turn ignition on. Measure voltage between ground and fuel pump relay terminal No. 1, located in engine compartment fuse/relay box. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, go to next step. If battery voltage does not exist, repair power supply circuit between fuse/relay box and battery.
3. Turn ignition off. Measure voltage between ground and fuel pump relay terminal No. 3. If battery voltage exists, go to next step. If battery voltage does not exist, check fuse No. 39 (20-amp). If necessary, replace fuse, and repair power supply circuit between fuse/relay box and battery. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).
4. Turn ignition off. Disconnect ECM connectors. Check for continuity in Blue/Purple wire between engine compartment fuse/relay box and ECM 24-pin connector C0635 terminal No. 18. (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If continuity exists, go to next step. If continuity does not exist, repair open in Blue/Purple wire.
5. Check for continuity between fuel pump relay terminals No. 1 and 2. If continuity exists, go to next step. If continuity does not exist, replace fuel pump relay.
6. Check for continuity between fuel pump relay terminals No. 3 and 5. If continuity does not exist, go to next step. If continuity exists, replace fuel pump relay.
7. Using a fused jumper wire, connect battery voltage to fuel pump relay terminal No. 1. Using another jumper wire, connect fuel pump relay terminal No. 2 to ground. When fuel pump relay is energized, check for continuity between fuel pump relay terminals No. 3 and 5. If continuity does not exist, replace fuel pump relay.

IDLE SPEED CONTROL (ISC) STEPPER MOTOR

See IDLE CONTROL SYSTEM (GEMS) .

1. Main relay may also be called the Multiport Fuel Injection Load relay. Main relay is an integral component of the multifunction relay unit, which is located in right rear of engine compartment. Disconnect connectors at multifunction relay unit. Check continuity with ohmmeter positive probe connected to multifunction relay unit 9-pin Black connector C1029 terminal No. 6 and negative probe connected to multifunction relay unit 6-pin Black connector C1030 terminal No. 3. (Scheme 30)and (Scheme 31). Continuity should exist. If continuity is as specified, go to next step. If continuity is not as specified, replace multifunction relay unit.
2. Reverse polarity of the ohmmeter. Continuity should not exist. If continuity is as specified, go to next step. If continuity is not as specified, replace multifunction relay unit.
3. Check continuity between multifunction relay unit 9-pin Black connector C1029 terminals No. 6 and 8, and between terminals No. 6 and 3. Continuity should not exist. If continuity is as specified, go to next step. If continuity is not as specified, replace multifunction relay unit.
4. Apply battery voltage to multifunction relay unit 9-pin Black connector C1029 terminal No. 6 and ground multifunction relay unit 6-pin Black connector C1030 terminal No. 3. Check continuity between multifunction relay unit 9-pin Black connector C1029 terminals No. 6 and 8, and between terminal No. 6 and 3. Continuity should exist. If continuity is as specified, fuel pump relay is okay. If continuity is not as specified, replace multifunction relay unit.

1. Main relay may also be called the Multiport Fuel Injection Load relay. Main relay is an integral component of the multifunction relay unit, which is located in right rear of engine compartment.
2. Using a backprobe set, measure voltage between ground and multifunction relay unit 8-pin connector terminal No. 6 (Brown/Light Green wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, go to step 4. If battery voltage does not exist, check fuse No. 7 (20-amp). If fuse is okay, go to next step. If fuse is not okay, repair short in Brown/Light Green wire and replace fuse.
3. Measure voltage on battery side of fuse No. 7 (20-amp). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If battery voltage exists, repair open in Brown/Light Green wire. If battery voltage does not exist, repair power supply circuit from battery. See appropriate wiring diagram in POWER DISTRIBUTION article in ACCESSORIES & EQUIPMENT.
4. Disconnect negative battery cable. Disconnect ECM Black 36-pin and 18-pin connectors. Check for continuity in Blue/Red wire between ECM Black 18-pin connector terminal No. 17 and multifunction relay unit 6-pin connector terminal No. 3. (Scheme 23) See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If continuity exists, go to next step. If continuity does not exist, repair open or short in Blue/Red wire.
5. Using a backprobe set, check for continuity between multifunction relay unit 8-pin connector terminals No. 6 (Brown/Light Green wire) and No. 3 (Brown/Orange wire), and between terminals No. 6 and No. 8 (Brown/Orange wire). If continuity does not exist, go to next step. If continuity exists, remove main relay and recheck relay unit for continuity between specified terminals. If continuity does not exist, go to step 8. If continuity exists, repair or replace multifunction relay unit.
6. Reconnect negative battery cable. Using a backprobe set, connect ECM Black 18-pin connector terminal No. 17 (Blue/Red wire) to ground. (Scheme 23) See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). Measure voltage between ground and multifunction relay unit 8-pin connector terminals No. 3 (Brown/Orange wire) and No. 8 (Brown/Orange wire), individually. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams).
7. If battery voltage exists at both terminals, substitute a known-good ECM and retest for original symptom or indication. If symptom or indication goes away, replace original ECM. If battery voltage does not exist, replace main relay and retest. If battery voltage still does not exist, check multifunction relay unit internal circuits. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). Repair or replace multifunction relay unit as necessary.
8. Remove main relay. Check for continuity between main relay coil terminals. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If continuity exists, go to next step. If continuity does not exist, replace main relay.
9. Using a fused jumper wire, connect battery voltage and ground to main relay coil terminals. Check for continuity between main relay switch terminals. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). If continuity exists, main relay is operating properly. If continuity does not exist, replace main relay. Remove battery ground and check for continuity between main relay switch terminals. If continuity exists, replace main relay.

1. Main relay may also be called the engine main control relay. Main relay is in the engine compartment fuse/relay box which is located at the right side of the engine compartment. Battery voltage is supplied directly to engine compartment fuse/relay box through Red wire from battery.
2. Before checking main relay, check inertia switch located on engine compartment firewall. Check for continuity between inertia switch terminals No. 1 (Brown/Black wire) and No. 3 (White/Green wire). If continuity exists, go to next step. If continuity does not exist, depress inertia switch plunger to reset switch. If continuity still does not exist, replace inertia switch.
3. Turn ignition off. Remove main relay from engine compartment fuse/relay box. Measure voltage between ground and main relay connector terminal No. 85. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If battery voltage is present, go to step 4 . If battery voltage is not present, check fuse No. 13 (15-amp) located in engine compartment fuse/relay box. Preform repairs as necessary. If fuse is okay, go to next step.
4. Measure voltage between ground and main relay connector terminal No. 30. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If battery voltage is present, go to next step. If battery voltage is not present, repair open in circuit between main relay and battery. If circuit can not be repaired, replace engine compartment fuse/relay box.
5. Using a backprobe set, check for continuity between main relay connector terminal No. 86 and ECM 24-pin connector terminal No. 23 (Blue/Red wire). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If continuity exists, go to next step. If continuity does not exist, repair open in circuit between main relay and ECM.
6. Check for continuity between main relay terminals No. 85 and 86. If continuity exists, go to next step. If continuity does not exist, replace main relay.
7. Check for continuity between main relay terminals No. 30 and 87. If continuity does not exist, go to next step. If continuity exists, replace main relay.
8. Using a fused jumper wire, connect battery voltage to main relay terminal No. 85. Using another jumper wire, connect main relay terminal No. 86 to ground. When main relay is energized, check for continuity between main relay terminals No. 30 and 87. If continuity does not exist, replace main relay.

1. Main relay may also be called the engine main control relay. Main relay is in the engine compartment fuse/relay box which is located at the right side of the engine compartment. Battery voltage is supplied directly to engine compartment fuse/relay box through Red wire from battery.
2. Turn ignition off. Remove main relay from engine compartment fuse/relay box. Measure voltage between ground and main relay connector terminals No. 1 and 3. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams) . If battery voltage is present at both terminals, go to next step. If battery voltage is not present, check for an open in Red wire between battery and engine compartment fuse/relay box. Repair as necessary. If Red wire is okay, repair or replace engine compartment fuse/relay box.
3. Check for continuity between main relay terminals No. 1 and 2. If continuity exists, go to next step. If continuity does not exist, replace main relay.
4. Check for continuity between main relay terminals No. 3 and 5. If continuity does not exist, go to next step. If continuity exists, replace main relay.
5. Using a fused jumper wire, connect battery voltage to main relay terminal No. 1. Using another jumper wire, connect main relay terminal No. 2 to ground. When main relay is energized, check for continuity between main relay terminals No. 3 and 5. If continuity does not exist, replace main relay.

FUEL SYSTEM PRESSURE RELEASE

Fuel pressure can be released at either the fuel supply line at the fuel rail or at the fuel filter. Position shop towel around fitting to protect against fuel spray. Carefully loosen fitting. When fuel pressure has been released, tighten fitting.

Fuel Pressure Test (Discovery)

Note. Regulated fuel pressure should be 35-37 psi (2.4-2.6 kg/cm 2 ) with engine at idle. Pressure will vary depending on amount of intake manifold vacuum acting on fuel pressure regulator.

1. Ensure engine temperature is less than normal operating temperature. If engine is at normal operating temperature, there may be abnormal pressure readings because of hot-soak fuel vaporization. Removing fuel filler cap may reduce effect of fuel vaporization. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-system-pressure-release) . Install fuel pressure gauge to fuel rail. Install shut-off valves in fuel supply and return lines. Activate fuel pump and bleed air from fuel pressure gauge.
2. Allow fuel pressure to stabilize and record fuel pressure. Turn fuel pump off and monitor gauge for changes in fuel pressure. If fuel pressure does not change, go to «FUEL INJECTOR BALANCE CHECK»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-injector-balance-test) . If fuel pressure decreases, close shut-off valve on fuel supply line and check fuel pressure. If fuel pressure decreases, go to next step. If fuel pressure does not decrease, check valve in fuel pump is faulty. Replace fuel pump.
3. If fuel pressure continues to decrease, close shut-off valve on fuel return line and check fuel pressure. If fuel pressure does not decrease, replace fuel pressure regulator. If fuel pressure continues to decrease, check fuel system for a leak. Repair as necessary. If no leaks are found, one or more fuel injectors may be leaking. Go to «FUEL INJECTOR BALANCE CHECK»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-injector-balance-test) .

Fuel Pressure Test (Discovery Series II & Range Rover)

Note. Regulated fuel pressure should be 50 psi (3.5 kg/cm 2 ) with engine at idle.

Fuel pump delivery pressure and pressure regulator operating pressure can be checked using a Schraeder type valve located at the rear of the engine on the fuel rail. The valve allows the pump delivery pressure to be measured using a suitable gauge and an adaptor and hose. If fuel pressure is not as specified at engine idle, ensure fuel line is not pinched, crushed or damaged and that there are no loose or leaking connections. If fuel lines are okay, replace fuel pump/sending unit assembly.

FUEL CONTROL

Fuel Pump Current Draw

The maximum fuel pump current draw should be 6.5 amps at 12.5 volts.

Fuel Injector Balance Test

1. Ensure engine temperature is less than normal operating temperature. If engine is at normal operating temperature, there may be abnormal pressure readings because of hot-soak fuel vaporization. Removing fuel filler cap may reduce effect of fuel vaporization. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-system-pressure-release) . Install fuel pressure gauge to fuel rail.
2. Connect fuel injector tester to No. 1 injector. Connect tester Red lead to battery positive terminal and Black lead to battery negative terminal. Activate fuel pump and bleed air from fuel pressure gauge. Turn fuel pump off and allow fuel pressure to stabilize. Record stabilized fuel pressure. Set fuel injector tester for a 500 mS pulse.
3. Using fuel injector tester, trigger fuel injector No. 1 and record stabilized fuel pressure. Move tester to fuel injector No. 2. Turn fuel pump on and allow fuel pressure to stabilize. Record stabilized fuel pressure. Trigger fuel injector No. 2 and record stabilized fuel pressure. Repeat procedure for remaining fuel injectors, recording fuel pressures before and after triggering each fuel injector. Ensure fuel system is pressurized before triggering each fuel injector.
4. Compare injector pressure drop for all injectors to the average pressure drop. Injector pressure drop is the difference between recorded pressures before and after fuel injector is triggered. For example, if the pressure before the injector is triggered is 30 psi and after is 16 psi, the injector pressure drop will be 14 psi. Add pressure drop values for all 8 injectors and divide by 8 to obtain the average fuel injector pressure drop.
5. The pressure drop for each injector should be within 2 psi (more or less than) of the average injector pressure drop. For example, if the average fuel pressure drop is 14 psi, then the injector pressure drop for each injector could be 12-16 psi.
6. Closely monitor injector pressure drop on each cylinder that has a misfire. If an injector is clogged or restricted, the injector pressure drop will be more than 2 psi greater (i.e.: more than 16 psi) than the average. If the injector is allowing to much fuel or is leaking, the injector pressure drop will be more than 2 psi less (i.e.: less than 12 psi) than the average. Replace any injector with a fuel pressure drop more than 2 psi greater or less than the average pressure drop. If pressure drop for all injectors are within 2 psi of the average, go to «FUEL INJECTOR ELECTRICAL CHECK»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__fuel-injector-electrical-test) .

Fuel Injector Electrical Test

1. Using a backprobe set, connect Snap-On Personal Automotive Computer (PAC) tester to suspect fuel injector driver terminal. See «IDENTIFYING FUEL INJECTOR DRIVER CONNECTOR TERMINALS (GEMS)»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing) or «IDENTIFYING FUEL INJECTOR DRIVER CONNECTOR TERMINALS (BOSCH)»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing) table. Set Snap-On PAC tester to 100 volt scale and 5.0 mS. Start engine and allow it to idle. Compare fuel injector wave pattern with known-good wave pattern. (Scheme 32)
2. If injector coil release spikes average approximately 80 volts, go to next step. An injector coil with a short will have average coil release spikes lower than 80 volts. Replace faulty fuel injector if coil release spikes average less than 80 volts.
3. Reset Snap-On PAC tester to 50 volt scale. Start engine and allow to idle. Check "On" time voltage for each injector. If "On" time voltage is constant at one volt or less, fuel injector drivers are operating properly. If "On" time voltage is not constant at one volt or less, go to next step.
4. If "On" time voltage is more than one volt, injector driver is not providing a consistent ground for the injector coil. Check for poor connections or loose wires between suspect fuel injector and ECM. See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). Perform repairs as necessary. If no problems are found, substitute a known-good ECM and recheck for original symptom or indication. If symptom or indication goes away, replace original ECM.

IDENTIFYING FUEL INJECTOR DRIVER CONNECTOR TERMINALS (GEMS)

IDENTIFYING FUEL INJECTOR DRIVER CONNECTOR TERMINALS (BOSCH)

Scheme 32

Turn ignition off. Disconnect IAC valve 4-pin connector. Measure resistance of IAC valve motor coils between terminals "A" and "D", and between "B" and "C". See WIRING DIAGRAMS . If resistance either coil is not 51-55 ohms, replace IAC valve and ensure warm idle position is 20-30 steps.

Turn ignition on. Using a backprobe set, measure voltage at ECM Red 36-pin connector terminal No. 18 (Orange/Black wire). With shift lever in Park or Neutral voltage should be zero. With shift lever in Drive, battery voltage should exist.

IDLE AIR CONTROL VALVE CIRCUIT (IACV)

Note. The ECM sets engine cold start idle speed and default idle speed at 1200 RPM. Although the engine idle speed is the same, one condition represents normal engine operation and the other does not.

1. IACV has a 3-pin connector and is located on the side of the intake air duct. IACV is used to maintain good quality idle speed under all operating conditions. IACV has 2 coils that use opposing PWM signals to control the open or closed positions of a rotary valve. IACV OPEN PWM signal is sent from ECM 52-pin connector C0636 terminal No. 42 (Red/Green wire). IACV CLOSE PWM signal is sent from ECM 52-pin connector C0636 terminal No. 43 (Blue/Gray wire). If one of the PWM signals fails, the ECM closes down the remaining signal causing the IACV to revert to a default position.
2. Check for an intake air system air leak. Check for blocked, restricted or crimped IACV actuator port or hoses.
3. Turn ignition off. Disconnect IACV 3-pin connector. Turn ignition on. Measure voltage between ground and IACV 3-pin connector terminal No. 2 (Brown/Orange wire). If battery voltage is present, go to step 5 . On Discovery Series II, if battery voltage is not present, check fuse No. 2 (15-amp) located in engine compartment fuse/relay box. On Range Rover, if battery voltage is not present, check fuse No. 37 (30-amp). On all models, if fuse is okay, go to next step. If fuse is not okay, replace fuse and recheck component operation.
4. Turn ignition off. Check for continuity in Brown/Orange wire between fuse and IACV 3-pin connector terminal No. 2. If continuity does not exist, repair Brown/Orange wire as necessary. If continuity exists, check main relay operation and circuit between fuse and ignition switch. Perform repairs as necessary.
5. Turn ignition off. Check for continuity in Red/Green wire between IACV 3-pin connector terminal No. 1 and ECM 52-pin connector C0636 terminal No. 43. If continuity exists, go to next step. If continuity does not exist, repair Red/Green wire as necessary.
6. Turn ignition off. Check for continuity in Blue/Gray wire between IACV 3-pin connector terminal No. 3 and ECM 52-pin connector C0636 terminal No. 42. If continuity exists, go to next step. If continuity does not exist, repair Blue/Gray wire as necessary.
7. Turn ignition off. Using a fused jumper wire, connect battery voltage to IACV terminal No. 2 (Brown/Orange wire). Using another jumper wire, alternately ground IACV terminals No. 1 (Red/Green wire) and No. 3 (Blue/Gray wire). Replace IACV if IACV actuator operation can not be detected.

IGNITION SYSTEM

Note. For basic ignition checks, see BASIC DIAGNOSTIC PROCEDURES article.

TIMING CONTROL SYSTEMS

Note. Ignition timing is controlled by Land Rover's Generic Engine Management System (GEMS) or Bosch Motronic 5.2.1 and is not adjustable.

ADVANCED EVAP SYSTEM (DISCOVERY)

Note. Temperature differences between vehicle and test equipment can cause misleading test results because of expansion and contraction of test gases during test. Ensure vehicle and test equipment temperatures are similar.

EVAP System Pressure Test

1. Ensure fuel filler cap is properly installed. Using Land Rover TestBook (use diagnostic disc DRG0002), close EVAP canister vent solenoid. Connect EVAPS Diagnostic Station System (LRA-19-004) to vehicle according to manufacturer instructions. Install Service Port Adapter (LRA-19-004-1) to line from fuel vapor separator, at EVAP canister. Connect EVAP diagnostic station Red hose to service port adapter. (Scheme 33)
2. Open valve on nitrogen cylinder. Turn control panel valve to PRESSURE position and pressurize EVAP system to 14.5 in. H2O. Turn control panel valve to OFF/HOLD position and monitor pressure gauge for 2 minutes. If pressure decrease is less than 6 in. H2O within 2 minutes, system is okay at this time. Go to step 4. If pressure decrease is more than 6 in. H2O within 2 minutes, go to next step.
3. Turn control panel valve to PRESSURE position and pressurize EVAP system to 30.0 in. H2O. Using an ultrasonic leak detector, check all system hoses, connections and joints for leaks. Repair as necessary and repeat EVAP system pressure test. When pressure test is completed, go to next step.
4. Insert Blue pressure release hose into pressure exhaust evacuation pipe. Turn control panel valve to PRESSURE RELEASE position. Using TestBook, open EVAP canister vent solenoid. Monitor pressure gauge until EVAP system pressure is zero inches of H2O. Turn control panel valve to OFF/HOLD position and close nitrogen cylinder valve. When repairs are completed, perform «EVAP SYSTEM PRESSURE TEST DRIVE CYCLE»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__evap-system-pressure-test-drive-cycle).

EVAP System Pressure Test Drive Cycle

1. Turn ignition on for 30 seconds. Ensure Engine Coolant Temperature (ECT) is less than 140°F (60°C).
2. Start engine and allow to idle for 2 minutes. Perform 2 light accelerations from zero to 35 MPH using light pedal pressure and slow to a stop. Perform 2 medium accelerations from zero to 45 MPH using moderate pedal pressure and slow to a stop. Perform 2 hard accelerations from zero to 55 MPH using heavy pedal pressure.
3. When second acceleration cycle is completed, increase vehicle speed to 60 MPH and continue for 5 minutes. Reduce speed to 50 MPH and continue for 5 minutes. Reduce speed to 35 MPH, continue for 5 minutes and slow to a stop.
4. Allow engine to idle for 2 minutes. Check for DTCs using Land Rover TestBook or OBD-II scan tool. If any DTC is indicated, perform specified repairs. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION table in appropriate SELF-DIAGNOSTICS article. If no DTCs are indicated, repair is complete.

Scheme 33

1. Ensure fuel filler cap is properly installed. Using Land Rover TestBook confirm that DTCs displayed relate to an EVAP system fault. Inspect components in fuel and EVAP system for damage or poor connections. (Scheme 34)or (Scheme 35). Repair or replace components as necessary. Reset Malfunction Indicator Lamp (MIL) using TestBook.
2. Perform Drive Cycle. See «EVAP SYSTEM PRESSURE TEST DRIVE CYCLE»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing). Using TestBook confirm that the Evaporative Loss Control (ELC) Inspection and Maintenance (IM) flag has cleared. This procedure should confirm that the ELC test was carried out during the drive cycle and that the fault was corrected.
3. If the IM flag is still indicated, use TestBook to check for a DTC is set or IM flag is still indicated, but no DTCs are set. If a DTC is set, perform DTC inspection and appropriate repairs. If a IM flag is still indicated, but no DTCs are set the conditions for the ELC check have not been met and the drive cycle must be repeated. Connect the EVAP Diagnostic Station to the service port and carry out the procedures given in the operating instructions supplied with the equipment. Perform repairs as indicated by the EVAP Diagnostic Station and repeat step 2.

1. Switch ignition on for 30 seconds. Ensure engine coolant temperature is less than 140°F (60°C). Start the engine and allow to idle for 2 minutes.
2. Perform 2 light accelerations, 0-35 mph, with light pedal pressure. Perform 2 medium accelerations, 0-45 mph, with moderate pedal pressure. Perform 2 hard accelerations, 0-55 mph, with heavy pedal pressure.
3. Increase speed to 60 mph and cruise for 8 minutes. Decrease speed to 50 mph and cruise for 3 minutes. Allow engine to idle for 3 minutes. Connect Testbook and check for DTCs.

Scheme 34

Scheme 35

1. When the engine is started, the ECM checks the engine coolant temperature. If Engine Coolant Temperature (ECT) indicates that coolant temperature is less than 131°F (55°C), ECM will activate the Secondary Air Injection (SAI) system. Ensure ECT sensor is operating properly.
2. ECT sensor ground is at ECM 52-pin connector C0636 terminal No. 21 (Red/Black wire). ECT sensor input analog 0-5 volt signal is at ECM 52-pin connector C0636 terminal No. 22 (Green wire). (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). (Scheme 36)
3. Battery voltage is supplied to the inertia switch via fuse No. 13 (10-amp) located in the engine compartment fuse/relay box. When inertia switch is closed, battery voltage is supplied to main relay coil. Main relay operation is controlled through ECM main relay coil ground at ECM 24-pin connector C0635 terminal No. 23 (Blue/Red wire). Ensure main relay is operating properly.
4. When main relay is energized, battery voltage is supplied to SAI pump relay coil via fusible link No. 2 (50-amp) located in the engine compartment fuse/relay box. SAI pump relay operation is controlled through ground at ECM 52-pin connector C0636 terminal No. 16 (Black/Orange wire).
5. When the main relay is energized, battery voltage is supplied the SAI vacuum solenoid valve via fuse No. 2 (15-amp) located in engine compartment fuse/relay box. SAI vacuum solenoid valve operation is controlled through ground at ECM 52-pin connector C0636 terminal No. 4 (Black/Blue wire). SAI vacuum solenoid valve is energized at the same time as the SAI air pump is energized.

Scheme 36

1. When the engine is started, the ECM checks the engine coolant temperature. If Engine Coolant Temperature (ECT) indicates that coolant temperature is less than 131°F (55°C), ECM will activate the Secondary Air Injection (SAI) system. Ensure ECT sensor is operating properly.
2. ECT sensor ground is at ECM 52-pin connector C0636 terminal No. 21 (Red/Black wire). ECT sensor input analog 0-5 volt signal is at ECM 52-pin connector C0636 terminal No. 22 (Green/Blue wire). (Scheme 24)and (Scheme 25). See «WIRING DIAGRAMS»(/land-rover/discovery/l318-1998-2002/remont/testing-diagnostics/#engine-controls-system-component-testing__wiring-diagrams). (Scheme 37)
3. When SAI pump relay is energized, battery voltage is supplied to relay coil connector terminal No. 5 via fusible link No. 2 (50-amp) located in the engine compartment fuse/relay box. SAI pump relay operation is controlled through ground at ECM 52-pin connector C0636 terminal No. 16 (Brown/Green wire).
4. When the main relay is energized, battery voltage is supplied to SAI vacuum solenoid valve connector terminal No. 1 (Brown/Pink wire) via fuse No. 26 (20-amp) located in engine compartment fuse/relay box. SAI vacuum solenoid valve operation is controlled through ground at ECM 52-pin connector C0636 terminal No. 4 (Pink/Blue wire). SAI vacuum solenoid valve is energized at the same time as the SAI air pump is energized.

Scheme 37

MISCELLANEOUS CONTROLS

Note. Although some of the controlled devices listed here are not technically engine performance components, they can affect driveability if they malfunction.

When A/C switch is turned on, a 12-volt A/C request signal will be seen at ECM Red 36-pin connector terminal No. 28 (Yellow/Black wire). When ECM confirms proper system operating conditions, a 12-volt A/C grant signal will be seen at ECM Black 36-pin connector terminal No. 1 (Black/Gray wire).

When A/C switch is turned on, an A/C request signal will be seen at ECM 40-pin connector C0637 terminal No. 16 (Yellow/Gray wire) and terminal No. 38 (Yellow/Black wire). The operation of the ATC request is via A /C switch being connected to ground.

WIRING DIAGRAMS

1. For 1999 Discovery, see «SYSTEM WIRING DIAGRAMS»(ref-120995) article in WIRING DIAGRAMS.
2. For 1999 Range Rover, see «SYSTEM WIRING DIAGRAMS»(ref-117866) article in WIRING DIAGRAMS.
3. For 2000 Discovery, see «SYSTEM WIRING DIAGRAMS»(ref-119053) article in WIRING DIAGRAMS.
4. For 2000 Range Rover, see «SYSTEM WIRING DIAGRAMS»(ref-119439) article in WIRING DIAGRAMS.

See also:
• WIRING DIAGRAMS
• CRANKSHAFT POSITION (CKP) SENSOR
• ENGINE COOLANT TEMPERATURE SENSOR RESISTANCE
• FUEL SYSTEM PRESSURE RELEASE
• FUEL INJECTOR BALANCE CHECK
• FUEL INJECTOR ELECTRICAL CHECK
• EVAP SYSTEM PRESSURE TEST DRIVE CYCLE