If you're traveling in the backcountry, one of the most discouraging things you can experience is a bright glowing "Check Engine" light staring back at you from the dashboard of your vehicle. Not only is the light disheartening, it's so vague that it's not really all that helpful. Something is wrong. What is wrong? Where did it go wrong? Is it serious?

Fortunately, all 3.9L V8 poweed NAS Land Rovers were equipped with an LED readout as part of their OBD (On Board Diagnostics). Unfortunately, all this LED gives you is a two digit code, which is equally meaningless unless you know what that code corresponds to.

The exact location of the LED reader varies based upon vehicle model and model year. Generally, it should be found near the ECU for the vehicle. On 1993 NAS Defender 110s and 1994 NAS Defender 90s the ECU is found on the passenger side kick panel against the firewall. On the 1994-95 Discovery the LED readout is under the passenger side seat, while on the 1995 NAS Defender 90, it is generally found in the cubby box, beneath the passenger seat.

On a side note, the position of the ECU on the 1995 Defender 90 makes it particularly susceptible to water damage during deep water crossings. Owners of this vehicle would be well advised to seal the bottom of the PS cubby box.

The LED box is black plastic, approximately 1" x 2.5" x 3" in size. Once you've located the display, simply put the key in the ignition and turn to the "on" position. Record the two digit code and cross reference with the list below. Then take steps to rectify the problem.

Once the problem is resolved, you can clear the code simply by disconnecting the vehicle battery for 30 seconds. If the check engine light returns, you will know that the mechanical problem is continuing to occur.

The fault codes are displayed on the LED in order of priority. If more than one fault exists, you have to clear the display before the next fault code will show up.

Below is an interpretation of what those codes translate are, as well as basic steps for rectifying some of the problems. All advice is done at your own risk. We suggest having a qualified mechanic do the repair work, or consulting a Land Rover shop manual for diagnosing and fixing the mechanical problems.

Click on the fault code below to go directly to the code diagnosis:

02

12

14

17

18

19

21

23

25

28

29

34

36

40

44

45

48

50

58

59

68

69

88

Code 02

The ECU has just been reconnected.
Switch on the ignition to clear the display.
Clearing the display. Switch ignition on. Disconnect serial link mating plug, wait 5 seconds, then reconnect.
Switch ignition off, wait for main relay to drop out.
Switch ignition on. The display should now be reset. If there are other faults, the next one will be displayed. Otherwise the display will be black.

If there is more than one fault, repeat steps 1-4 to clear each fault until the display is blank. If no LEDs are on: Good news, nothing is wrong. Either that or the LEDs are burned out or the display isn't getting any power.

Code 12

Airflow meter
Refer to service test 19, continuity test procedure.

Code 14

Coolant Thermistor
Refer to service test 14, continuity test procedure.

Code 17

Throttle Potentiometer
Refer to service test 17, continuity test procedure.

Code 18

Throttle Potentiometer Input high/
airflow meter low
Refer to service tests 17, 18 and 19, continuity test procedure.

Code 19

Throttle Potentiometer Input Low/
airflow meter High
Refer to service tests 17, 18 and 19, continuity test procedure.

Code 21

Fuel Tune Select
Identifies that the tune select resistor is open circuit - refer to tune select resistor test in service manual.

Code 23

Fuel Supply
Check fuel system pressure - test 20 of continuity test procedure.

Code 25

Ignition Misfire
This code indicates that an ignition system misfire has been detected. Codes 40 and 50 indicate on which bank the misfire has occurred.

Code 28

Air Leak
Check for air leaks in the following areas:
Hose, air flow meter to plenum
Breather system hoses to plenum
Brake servo hose
Vacuum reservoir hose (fresh air solenoid)
Distributor vacuum advance
Hose, purge valve to plenum
Injector seals
Joint - bypass air valve to plenum, plenum chamber to ram housing, ram housing to inlet manifold, manifold to cylinder head

Code 29

ECU Memory Check
If detected, all other fault codes are unreliable and must be ignored.
Procedure:
1. Leave battery connected
2. Switch ignition off
3. Wait for approximately 5 seconds
4. Disconnect ECU plug
5. Reconnect ECU plug
6. Switch ignition on and check display unit
If fault code 29 is detected again, swap out the ECU for another one and retest.

Code 34

Injector Bank A
The display will indicate if the injector(s) are causing the engine to run rich or lean. If the bank is running rich, check for faulty injector wiring and connectors, stuck open injectors. If the bank is running lean, check for faulty injector wiring and connectors, blocked injectors.

Code 36

Injector Bank B
Same testing and procedures as Code 34, except relevant to bank A injectors.

Code 40
CODE 50

Misfire, Bank A (Left bank)
Misfire, Bank B (Right Bank)
If both codes are displayed, check the following components common to both banks:
Distributor cap
Rotor arm
Coil
Electrical connections
Pick-up (air gap)
Amplifier
Injectors (if code 34 or 36 is displayed)
If just either code 40 or 50 is displayed, check components specific to that particular bank that the misfire has occurred on. ie - spark plugs, HT leads, distributor cap.

Code 44
Code 45

Lambda (Oxygen) Sensor A - Left bank
Lambda (Oxygen) Sensor b - Right bank
If one of these fault codes is displayed, check the wiring to that particular lambda sensor. If both codes are displayed, the voltage supply to the heater coils of the sensors must be checked. Refer to test 26, continuity test procedure.

Code 48

Stepper motor
Check base idle speed - see setting procedure. Refer to tests 15 and 16 of continuity test procedure. Check road speed sensor - refer to test 25 of the continuity test procedure.

Code 58

group Faults 23/28
This indicates that a fault has been registered that is caused by the fuel supply or an air leak but the exact fault cannot be identified. Check all items outlined under codes 23 and 28 (above).

Code 59

Fuel thermistor
Refer to test 13 of the continuity test procedure.

Code 68

Road Speed sensor
Refer to test 25 of the continuity test procedure.

Code 69

Gearswitch
Refer to test 24 of the continuity test procedure.

Code 88

Purge Valve Leak
Refer to test 9 and 10 of the continuity test procedure.