Engine Performance Self-Diagnostics Land Rover Discovery I

INTRODUCTION

To properly diagnose and repair this vehicle, follow TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM. If no trouble codes are present and a no start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If no trouble codes are present and a driveability condition exists, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

TESTING PROCEDURE

To carry out tests when 40 way connector is connected to the ECM, it is necessary to remove the two screws securing the shroud to the connector to enable the multi-meter probes to be inserted into the back of the appropriate pin. (Scheme 7) For pin number identification, pin numbers 1, 13, 14, 27, 28 and 40 are molded onto rear of connector. (Scheme 7) To gain access to ECM remove front seat base trim of front right seat.

1. Before proceeding with testing vehicle, perform preliminary checks. See «PRELIMINARY CHECKS»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-performance-self-diagnostics__preliminary-checks) . If no problem is present, go to next step.
2. If engine cranks but does not start, no diagnostic trouble codes are set and scan tool can communicate with ECM, see «NO DIAGNOSTIC TROUBLE CODE TEST»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-performance-self-diagnostics) .
3. If Lucas Diagnostic Equipment or Test Book cannot communicate with the ECM and engine cranks but does not start, go to next step. If scan tool other then Lucas Diagnostic Equipment or Test Book cannot communicate with ECM and engine cranks but does not start, see scan tool manufacturers procedure for checking scan tool performance. If no problem is present, check engine control module power and ground circuits, see «ENGINE CONTROL MODULE POWER & GROUND TEST»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-performance-self-diagnostics) .
4. Check Lucas Diagnostic Equipment or Test Book connections. If connections are okay, go to next step.
5. On Lucas Diagnostic Equipment check that the memory card is correct and inserted properly. On Test Book check that CD is correct and inserted properly. Check Lucas Diagnostic Equipment or Test Book internal power source. If no problem is present, check engine control module power and ground circuits, see «ENGINE CONTROL MODULE POWER & GROUND TEST»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-performance-self-diagnostics) .

PRELIMINARY CHECKS

1. Check that the inertia fuel shutoff switch is not tripped. Inertia fuel shutoff switch is located beneath left front seat (on 1993-94 models) or on right side of fire wall at back of engine compartment (on 1995 models). (Scheme 1)or (Scheme 2).
2. Check main and fuel pump relay fuses.
3. Check for ample fuel in tank.
4. Check air inlet system for possible leaks into the intake manifold.
5. Check spark plug wires for correct firing order, routing and visual damage. See appropriate SPECIFICATIONS article.
6. Check ignition timing. See appropriate SPECIFICATIONS article.

Only when the above checks have been carried out, should circuit diagnosis begin.

Scheme 1

Scheme 2

RETRIEVING DIAGNOSTIC TROUBLE CODES

The Engine Control Module (ECM) is capable of storing fault codes. A lit service engine warning light indicates that a fault is present. For U.S. vehicles, these fault codes may be read by switching the ignition switch to ON position and observing the fuel injection fault display unit. Fuel injector fault display unit is located beneath right front seat. (Scheme 5)or (Scheme 6). The codes are displayed one at a time in the order of system priority. See DIAGNOSTIC TROUBLE CODE ORDER OF SYSTEM PRIORITY under DIAGNOSTIC TROUBLE CODE DEFINITIONS. To view the next code, when multiple codes are stored, the previous code must be cleared. See CLEARING DIAGNOSTIC TROUBLE CODES. If no other codes are present, the display will appear blank.

CLEARING DIAGNOSTIC TROUBLE CODES

Note. Serial link can also be referred to as data link connector or MFI data link connector. Main relay can be also be referred to as fuel injection load relay.

It is necessary to clear code displayed when fault has been rectified or to view the following code when more then one code is stored. Clear fault code displayed using following procedure

1. Switch ON ignition.
2. Disconnect White 5-pin serial link connector, wait 5 seconds and reconnect. Serial link connector can be located beneath right front seat (on 1993-94 models) or behind right side of fascia (on 1995 models). (Scheme 3)or (Scheme 4).
3. Switch OFF ignition, wait for fuel injection load relay to turn off.
4. Switch ON ignition. The display should now reset. If no other faults exist, and original fault has been rectified, display will be blank. If other faults exist, they will be displayed at this time.
5. If multiple faults exist, repeat steps 1 - 4 as each fault is cleared the code will change to the next one in order of system priority, until all faults are cleared. See «DIAGNOSTIC TROUBLE CODE ORDER OF SYSTEM PRIORITY»(/land-rover/discovery/i-1989-1998/remont/testing-diagnostics/#engine-performance-self-diagnostics) under DIAGNOSTIC TROUBLE CODE DEFINITIONS. The display will now be blank.

SUMMARY

If no trouble codes are present and a no start condition exists, proceed to appropriate BASIC DIAGNOSTIC PROCEDURES article. If no trouble codes are present and a driveability condition exists, proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, ENGINE STALLS, etc.).

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DIAGNOSTIC TROUBLE CODE ORDER OF SYSTEM PRIORITY

Scheme 3

Scheme 4

Scheme 5

Scheme 6

ENGINE CONTROL MODULE

CONNECTOR IDENTIFICATION

There are six pin numbers 1, 13, 14, 27, 28 and 40 molded onto the rear of the connector. (Scheme 7)

CONNECTOR IDENTIFICATION

Scheme 7

DIAGNOSTIC TESTS

Note. For identification of circuits, terminals and wire colors referenced in the following testing, see WIRING DIAGRAMS .

Scheme 8

Scheme 9

Scheme 10

Scheme 11

Scheme 12

Scheme 13

Scheme 14

Scheme 15

Scheme 16

Scheme 17

Scheme 18

Scheme 19

CODE 02: RECONNECTED ECM FAULT

Code 02 will show if the Engine Control Module (ECM) has just been reconnected. Switch ON ignition to clear the display.

Code Set Criteria

Code will set if Mass Airflow (MAF) sensor signal is less than 1.22 volts with engine running, or greater than 4.96 volts with engine speed less than 976 RPM for more than 1.6 seconds.

Diagnostic Procedure

Test mass airflow sensor. Perform Test "D". (Scheme 20)- (Scheme 22). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment (Test Book).

Scheme 20

Scheme 21

Scheme 22

Code will set if Engine Coolant Temperature (ETC) sensor signal is out of range (0.15-4.9 volts) for more than 1.6 seconds.

Test coolant temperature sensor. Perform Test "E". (Scheme 23) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 23

Code will set if Fuel Temperature Sensor (FTS) signal is out of range (0.08-4.9 volts) for more than 1.6 seconds.

Test fuel temperature sensor. Perform Test "F". (Scheme 24) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 24

Code will set if Throttle Position Sensor (TPS) output is less than 0.78 volts for more than 1.6 seconds.

Test Throttle Position (TP) sensor. Perform Test "G". (Scheme 25)and (Scheme 26). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 25

Scheme 26

CODE 18: THROTTLE POSITION SENSOR INPUT HIGH/MASS AIRFLOW SENSOR INPUT LOW FAULT

Test Throttle Position (TP) sensor and Mass Airflow (MAF) sensor. Perform Test "H". (Scheme 27)and (Scheme 28). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 27

Scheme 28

CODE 19: THROTTLE POSITION SENSOR INPUT LOW/MASS AIRFLOW SENSOR INPUT HIGH FAULT

Test Throttle Position (TP) sensor and Mass Airflow (MAF) sensor. Perform Test "H". (Scheme 27)and (Scheme 28). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

CODE 21: TUNE SELECT RESISTOR FAULT

To suit individual market requirements, a tune select resistor is connected across terminals No. 5 and 27 of Engine Control Module (ECM). Tune select resistor is located adjacent to ECM, and strapped to CHECK ENGINE cable assembly. Value of resistor is dependent on market application. For USA models, resistor (with White wire) value is 3900 ohms. Code 21 identifies that the tune select resistor is open circuit. To test tune select resistor, perform Test "A". (Scheme 29) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 29

CODE 23: FUEL SUPPLY FAULT

1. Remove fuel pump relay. Fuel pump relay is located under passenger seat. see scheme 30 Start and run engine.
2. When sufficient fuel has been used to cause fuel line pressure to drop, injectors will become inoperative, resulting in engine stall. Switch off ignition. Disconnect the battery negative lead.
3. Disconnect fuel filter outlet pipe, located on the chassis under the right rear wheel arch. (Scheme 30) Connect the pressure gauge on the outlet from the filter.
4. Reconnect the battery and turn the ignition to ON position, while observing pressure gauge. Pressure should be 2.39-2.67 kg/cm 2 (34-38 psi). Maximum allowable pressure drop is 0.7 kg/cm 2 (10 psi) per minute. If pressure is low, ensure filter is not blocked and pump is operating correctly, recheck pressure. If pressure is still low renew regulator. Repair or replace fuel pressure regulator as necessary. After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

CODE 28: ENGINE AIR LEAK FAULT

Check for air leaks in following areas

1. Hose, mass airflow sensor to plenum.
2. Breather system hoses to plenum.
3. Brake servo hose.
4. Vacuum reservoir hose (fresh air solenoid).
5. Distributor vacuum advance.
6. Hose, purge valve to plenum.
7. Injector seals.
8. By pass air valve to plenum.
9. Plenum chamber to ram housing.
10. Ram housing to inlet manifold.
11. Inlet manifold to cylinder head.
12. Bypass air valve hose.

CODE 29: ECM MEMORY FAULT

If fault Code 29 is detected, all other faults are unreliable and must therefore be ignored. Code 29 indicates an ECM memory fault. To test ECM, perform Test "I". (Scheme 31)

Scheme 30

CODE 34: LEFT BANK INJECTOR FAULT (BANK "A")

Test fuel injectors, perform Test "J". (Scheme 32) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 31

CODE 36: RIGHT BANK INJECTOR FAULT (BANK "B")

Test fuel injectors, perform test "J". (Scheme 32) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

CODE 40: LEFT BANK MISFIRE FAULT (BANK "A")

If code 50 is displayed along with code 40, check distributor cap, rotor, coil, electrical connections, pick-up (air-gap), amplifier or, if code 34 is displayed check injectors. See CODE 34: LEFT BANK INJECTOR FAULT (BANK "A") . If only code 40 is displayed check right bank component. Check spark plugs, plug wires, distributor cap, if code 34 is displayed check injectors. See CODE 34: LEFT BANK INJECTOR FAULT (BANK "A") .

Code will set if left bank Heated Oxygen Sensor (HO2S) will not switch after Engine Control Module (ECM) had radically altered fueling on left bank of injectors. Test is performed when engine is at normal operating temperature, Throttle Position (TP) sensor signal is above 2 volts, and a road speed signal is received.

Test HO2S. Perform Test "K". (Scheme 33)and (Scheme 34). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 32

Scheme 33

Scheme 34

Scheme 35

Code will set if right bank Heated Oxygen Sensor (HO2S) will not switch after Engine Control Module (ECM) had radically altered fueling on right bank of injectors. Test is performed when engine is at normal operating temperature, Throttle Position (TP) sensor signal is above 2 volts, and a road speed signal is received.

Test HO2S. Perform Test "K". (Scheme 33)and (Scheme 34). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

CODE 48: IDLE AIR CONTROL VALVE FAULT

Check base idle speed. See appropriate ON-VEHICLE ADJUSTMENTS article. If base idle speed is okay, test idle speed stepper motor. Perform Test "M". (Scheme 37)and (Scheme 38). After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 36

Scheme 37

CODE 50: RIGHT BANK MISFIRE FAULT (BANK "B")

If code 40 is displayed along with code 50, check distributor cap, rotor, coil, electrical connections, pick-up (air-gap), amplifier or, if code 36 is displayed check injectors. If only code 50 is displayed check right bank component. Check spark plugs, plug wires, distributor cap, if code 36 is displayed, check injectors. See CODE 36: RIGHT BANK INJECTOR FAULT (BANK "B") .

CODE 59: GROUP FAULTS 23/28

This indicates that a fault has been registered that is caused by fuel supply or an air leak, but exact fault cannot be identified. Check all items outlined under CODE 23: FUEL SUPPLY FAULT and CODE 28: ENGINE AIR LEAK .

Code will set if Mass Airflow (MAF) sensor signal is greater than 3 volts with engine speed at 2000-3000 RPM.

Note. If speedometer does not operate, see appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.

Test vehicle speed sensor signal. Perform Test "N". (Scheme 39) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 38

Code will set if when park/neutral position switch signal is 5 volts during cranking or zero volts with engine speed above 2663 RPM and Mass Airflow (MAF) sensor signal is more than 3 volts.

Test park/neutral position switch. Perform Test "O". (Scheme 40) After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 39

CODE 88: CANISTER PURGE VALVE LEAK FAULT

Test purge control solenoid valve. Perform Test "P". (Scheme 41)and see scheme 43. After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas Diagnostic Equipment or Test Book.

Scheme 40

Scheme 41

WIRING DIAGRAMS

1. For 1993 Defender 110 & 1994 Defender 90, see «ENGINE PERFORMANCE»(ref-137610-S29482404332002030800000) in SYSTEM WIRING DIAGRAMS article in WIRING DIAGRAMS.
2. For 1995 Defender 90, see «ENGINE PERFORMANCE»(ref-138158-S01244690182002032500000) in SYSTEM WIRING DIAGRAMS article in WIRING DIAGRAMS.
3. For 1995 Discovery, see «ENGINE PERFORMANCE»(ref-137618-S31844388562002030800000) in SYSTEM WIRING DIAGRAMS article in WIRING DIAGRAMS.

See also:
• TESTING PROCEDURE
• PRELIMINARY CHECKS
• NO DIAGNOSTIC TROUBLE CODE TEST
• CLEARING DIAGNOSTIC TROUBLE CODES
• Code 02
• Code 18
• Code 19
• Code 21
• Code 23
• Code 28
• Code 29
• Code 34
• Code 36
• Code 40
• Code 48
• Code 50
• Code 59
• Code 88
• WIRING DIAGRAMS