Last Updated 31 May 2000
Most people are aware of the 'Engine Fault' light on the dash board, but not many know what it means when it comes on. Basically, when illuminated, it indicates that the ECU is not happy with one or more of the inputs it is receiving from the engine sensors. In most circumstances, the ECU ignores the input that it believes is faulty, and starts to 'assume safe' values. This is often termed 'Limp Home Mode'. It also lights the CEL (Check Engine Light) to tell the driver that a fault exists. Unless you know a lot about engine diagnostics, all you can do is take the car to the nearest LC approved garage, and let them charge you an arm and a leg for changing the offending sensor (You can't go to a normal Vauxhall Garage because they don't have the required program cartridge for the Tech 1 engine diagnostic tool).
However, it is possible for any reasonably competent person to diagnose and repair most faults. The only piece of equipment you need is - a paper clip, or short length of wire. Open the bonnet, and locate the ECU ALDL plug. It's at the back of the engine bay on the left hand side (looking from the front of the car), above the brake servo (for RHD Carltons. - on LHD Omegas its above the Air Conditioning Drier/Accumulator). There are acutally 2 ALDL connectors, one dedicated to the ECU, and one for other systems, including the alarm, and possibly the Antilock Brake System (not certain about this last one). The ECU ALDL plug is the one with just 4 wires in it, coloured Brown, White+Black striped, Orange and Purple.
Once you have located the correct ALDL plug, pull off the blanking cover. The ALDL connectors have blanking cover plug inserted into them to prevent water getting in. Pull off this blanking cover plug by releasing the locking clip. Once the blanking cover is off, you should have full access to the ALDL plug. It has 4 wires connected into it, as follows (The colours shown are the colours in my car, but I believe all cars to be the same).
Insert the paper clip in the position shown, so that it connects terminals A (Brown wire) to B (Black/White striped wire). When you do this, the Auxillary Water Pump (AWP) and the Auxillary Electric Fan (AEF) should start. .The AEF will run at full speed, and make quite a lot of noise. However, you should be able to hear and feel the AWP humming/whirring/buzzing. You may also see water being returned into the expansion tank. If either the AWP or AEF do not start, then you have a fault which could cause your engine to overheat, and cause serious (and expensive) damage. Get them fixed before summer arrives !
Then sit inside the car and turn the ignition on - BUT DO NOT START THE ENGINE. Instead, look at the CEL - It should be blinking out Trouble Codes (TC), also know as blink codes. To decode the TC count the blinks and pauses. For example, Trouble Code 24 (TC24) will be blinked out as follows:
BLINK - BLINK - PAUSE - BLINK - BLINK - BLINK - BLINK - PAUSE
Each BLINK lasts about half a second, and the PAUSE between digits of the code lasts about a second. Each TC will be blinked out three times. With the engine off, the CEL will blink out TC12 three times. This does not indicate a fault, it simply means that the ECU is not receiving an input from the crankshaft sensor (becaause the engine isn't running !) However once the CEL has blinked out TC12 three times, it will continue and blink out any real trouble codes (3 times each) before beginning again with three TC12's. So in a healthy engine/ECU, all you should get is a continuous stream of TC12's. But if you get any other TC's then you need to know what they mean.
| Trouble Code | Meaning | Probable Cause |
| TC13 | Front Oxygen Sensor Open Circuit | Bad Lambda Sensor |
| TC14 | Coolant Temperature Sensor High | Coolant Temp Sensor Faulty |
| TC15 | Coolant Temperature Sensor Low | Coolant Temp Sensor Faulty |
| TC16 | Turbo Wastegate Overboost | Faulty Turbo Wastegate Faulty Wastegate Solenoid Manifold Air Pressure Sensor Faulty |
| TC21 | Throttle Position Sensor High | Faulty Throttle Position Sensor |
| TC22 | Throttle Position Sensor Low | Faulty Throttle Position Sensor Throttle Position Sensor badly adjusted |
| TC23 | Manifold Air Temperature Sensor High | Faulty (short circuit) Manifold Air Temperature Sensor No coolant in Charge Cooler |
| TC24 | No Vehicle Speed Signal | Faulty Gearbox Speed Sensor |
| TC25 | Manifold Air Temperature Sensor Low | Faulty (open circuit) Manifold Air Temperature Sensor |
| TC31 | Camshaft Speed Sensor Signal | Faulty Camshaft Sensor Timing Chain Broken - TC31 is the least of your problems here ! |
| TC33 | Manifold Air Pressure Sensor High | Faulty Manifold Air Pressure Sensor Turbo Wastegate or Solenoid failure |
| TC34 | Manifold Air Pressure Sensor Low | Faulty Manifold Air Pressure Sensor |
| TC41 | Cylinder Select Error | Faulty ECU - Has the ECU been chipped ? |
| TC42 | Bypass or EST Line Failure | Faulty Ignition Coil Pack |
| TC43 | Knock Sensor Circuit | Faulty Knock Sensor Extremly poor fuel quality - 95 RON or better is reccomended. |
| TC44 | Front Oxygen Sensor Lean Exhaust | Bad Lambda Sensor |
| TC45 | Front Oxygen Sensor Rich Exhaust | Bad Lambda Sensor |
| TC51 | ECU or EPROM error | Faulty ECU - Has the ECU been chipped ? |
| TC53 | Battery Voltage High | Faulty Alternator or Battery Faulty ECU |
| TC63 | Rear Oxygen Sensor Open Circuit | Bad Lambda Sensor |
| TC64 | Rear Oxygen Sensor Lean Exhaust | Bad Lambda Sensor |
| TC65 | Rear Oxygen Sensor Rich Exhaust | Bad Lambda Sensor |
| TC66 | Turbo Boost System Out Of Limits | Faulty Wastegate Solenoid Manifold Air Pressure Sensor Faulty |
As you can see, most of the TC's can be put down to sensor faults. However, before you go and buy a new sensor, make sure it isn't a simple wiring problem. Unplug the suspect sensor and inspect the connector and wiring for signs of water damage or corrosion. Where applicable, clean the sensor and any contacts to it, and re-assemble. It the CEL light doesn't come on next time you start the engine (with the paper clip removed from the ALDL plug) , then that may have been the cause of the fault. But keep a close eye on the CEL for the next few days and weeks, to make sure the fault doesn't re-occur.
The only TC's that I would consider beyond my abilities to attempt to fix would be TC41 and TC51, both of which indicate a failure within the ECU itself. If you get either of these, then I fear you may need a new ECU, which will be VERY VERY expensive from Vauxhall. However, I have found a source of these in the USA for only $105 + p&p (about $150 total) . EMAIL me if you want more information.