Later model RRC came with a on board diagnostic reader for the check engine light. A rather simple but clever design allows us to figure out why the light is on but also displays multiple codes to make life a little easier. Under the right seat are to computer and a black box about 2"X3" the has a sticker that reads Range Rover On Board Diagnostic Display, it will display one code at a time in big easy to read red analog letters. Below are the pictures of the plugs and display, as well as instructions for resetting and reading multible codes. This should be made a sticky for future owners.

Description of fault codes
The fault codes are listed in order of priority. Where more than one fault exists, clearing the first fault code will permit the next code to be displayed.

Note: Fault code 02 will show if the ECU has been reconnected. Switch on ignition to clear the display.

Clearing fault code display
It is necessary to clear the code displayed when the fault has been rectified, and to access any fauther fault codes that may exist. Clear the fault code display using the following procedure:
1. Switch on the ignition.
2. Disconnect serial link mating plug, wait 5 seconds, reconnect.
3. Switch off ignition. Wait for the main relay to drop out.
4. Switch on ignition, the display should now reset, If no other faults exist the display will be blank.
5. If mulitiple faults exist repeat steps 1-4 til each fault is cleared.

Codes and their translations:
Code 29: ECU memory check - If this fault is present all other faults are unrelible and must be ignored.

Proceed as followed:
1. Leave battery connected
2. Switch off ignition
3. Wait 5 seconds
4. Disconnect ECU plug
5. Reconect ECU plug
6. Switch on ignition and check display unit.

Note: If fault Code 29 is present again restart test sequence.

Code 44 - Left oxygen sensor
Code 45 - Right oxygen sensor

Code 25 - Ignition Misfire - This code indicates that a misfire has been detected, code 40 or 50 will indicate which bank the misfire has occured.

Code 40 - Misfire bank A - left bank
Code 50 - Misfire bank B - right bank

If both fault codes are present check the following components:
- Distribitor cap
- Rotor arm
- Coil
- Electrical connectors
- Pick- up (air gap)
- Amplifier
- Injectors if Codes 34 or 36 are displayed.

If either Code 40 or 50 is displayed check components applicable to the particular bank that has had the misfire.
- Spark plugs HT leads
- Distributor cap
- Injectors if Codes 34 or 36 are displayed.

Code 12 - Mass airflow sensor

Code 21 - Fuel tune selector - Identifies that the tune selector circuit is open.

Code 34 - Injector Bank A - The display will indicate if the injectors are causing the engine to run rich or lean.

Code 36 - Injector Bank B - The display will indicate if the injectors are causing the engine to run rich or lean.

Code 14 - Coolant Thermistor

Code 17 - Throttle Potentiometer

Code 18 - Throttle potentiometer input high/airflow meter low

Code 19 - Throttle potentiometer input low/airflow meter high

Code 88 - Purge valve leak

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
- Distribitor vacuum advance
- Hose, purge valve to plenum
- Injector seals

Code 23 - Fuel Supply - Check fuel supplie pressure

Code 48 - Stepper motor

Code 68 - Road speed sensor

Code 69 - gearswitch

Group 58 - Group faults 23/28 - This indicates that a fault has been resistered that is caused by the fuel supply or an air leak but the exact fault cannot be identified. Check all items outlined under code 23 and 28.

Code 15 - Fuel Thermistor

The second plug, one one the floor, is the serial link mating plug as well and the ECU plug.

This is the On Board Diagnostic Display, the black box with a sticker on it.