ECU Fault Codes Explained
What are 'fault codes'?
Fault codes are recognised problems or faulty sensors to the EMU (Engine Management Unit) which is a ECU (Electronic Control Unit). The ECU relies on the sensors on your car to make it run at it's optimum performance at all times. When a sensors goes wrong or there is a fault with the engine, the ECU sees this problem and logs the fault code within it's memory (NOTE: not ALL problems are logged, depends on what system your car has). Often the ECU warning light on the dash board may light up, indicating to you that there is a problem.
NOTE: The ECU warning lamp usually needs to be on for more than 30 seconds before the ECU logs a fault code. Otherwise it could consider it an intermittent fault and ignore it.
Do all ECU's handle fault codes?
If your engine is fuel injected then it needs a ECU to control the injection timing. All Vauxhall models that have injection need a ECU to do this and hence they will have the facility to log fault codes. If your engine is run on a carburetor, then it has no ECU, hence no fault codes can be logged or read.
How do I read the fault codes?
There are two common ways to do this. The first is to use a TECH1 or a TECH2 reader which is an expensive bit of equipment. Some dealerships could charge you £50 just to connect it up to your car. The second option is FREE and YOU can do it....with a paper clip.
The paper clip method flashes the ECU warning lamp on the dash, and you read the amount of flashes and pauses. The chart supplied in this article tells you what the fault code means. The paper clip is used to short out two pins in the ALDL connector (also know as 'diagnostics plug' or 'test connector'). These are commonly coloured blue and can be located in the car or within the cabin, depending on model of car and fueling system.
It doesn't matter if the engine is running or not when the flash codes are being read out. In fact it is beneficial to have the engine running since on some ECU's, if it doesn't see the engine running, it will produce a fault code straight away and gives a misleading fault code.
Please note on newer ECU cars in the region of 2000 onwards, most now use ECU codes which can not be read out via the paper clip method. You will have to consult a ECU/fault code specialist or your nearest Vauxhall/Opel Dealer.
What pins do I short out?
If you have Motronic or GM-Multec fuel system, then you'll find a 10-pin ALDL connector. To read the flash codes, then short pins A and B (see figure 1).
If its a Simtec 56.0 or 56.1 fuel system (i.e. Ecotec engine) then you'll find a 10-pin ALDL connector. To read the flash codes you need to short pins A and B (see figure 1).
If its a Simtec 56.5 fuel system (i.e. Ecotec engine) then you'll find a 16-pin ALDL connector. To read the flash codes (P codes) you need to short out pins 5 and 6 (see figure 6).
Can I damage anything if I short the wrong pins?
Yes it is possible but unlikely, depending on what pin you short out. Most of them are 0v connections, but there are live +12v supply pins on there as well depending on which ALDL plug you have. If you are in doubt, don't do it! Double check the diagrams shown.
Where do I find the ALDL connector on the car?
Again if you have a Motronic or GM-Multec system, then these are commonly found in the engine bay or within the fuse box. Look for a 10-pin connector which is usually plugged into a blanking socket (i.e. not actually connected to anything). See figures 2, 3 and 5.
However if you have a Simtec 56.0 or 56.1 system, then the 10-pin ALDL connector can also be found in the engine bay or within the fuse box. See figures 2, 3 and 5.
However if you have a Simtec 56.5 system, then the 16-pin ALDL connector can be found in the fuse box area or under the trim to the hand brake or under the bulge in the carpet beside the passenger front seat. See figures 7 and 8.
Fault codes are recognised problems or faulty sensors to the EMU (Engine Management Unit) which is a ECU (Electronic Control Unit). The ECU relies on the sensors on your car to make it run at it's optimum performance at all times. When a sensors goes wrong or there is a fault with the engine, the ECU sees this problem and logs the fault code within it's memory (NOTE: not ALL problems are logged, depends on what system your car has). Often the ECU warning light on the dash board may light up, indicating to you that there is a problem.
NOTE: The ECU warning lamp usually needs to be on for more than 30 seconds before the ECU logs a fault code. Otherwise it could consider it an intermittent fault and ignore it.
Do all ECU's handle fault codes?
If your engine is fuel injected then it needs a ECU to control the injection timing. All Vauxhall models that have injection need a ECU to do this and hence they will have the facility to log fault codes. If your engine is run on a carburetor, then it has no ECU, hence no fault codes can be logged or read.
How do I read the fault codes?
There are two common ways to do this. The first is to use a TECH1 or a TECH2 reader which is an expensive bit of equipment. Some dealerships could charge you £50 just to connect it up to your car. The second option is FREE and YOU can do it....with a paper clip.
The paper clip method flashes the ECU warning lamp on the dash, and you read the amount of flashes and pauses. The chart supplied in this article tells you what the fault code means. The paper clip is used to short out two pins in the ALDL connector (also know as 'diagnostics plug' or 'test connector'). These are commonly coloured blue and can be located in the car or within the cabin, depending on model of car and fueling system.
It doesn't matter if the engine is running or not when the flash codes are being read out. In fact it is beneficial to have the engine running since on some ECU's, if it doesn't see the engine running, it will produce a fault code straight away and gives a misleading fault code.
Please note on newer ECU cars in the region of 2000 onwards, most now use ECU codes which can not be read out via the paper clip method. You will have to consult a ECU/fault code specialist or your nearest Vauxhall/Opel Dealer.
What pins do I short out?
If you have Motronic or GM-Multec fuel system, then you'll find a 10-pin ALDL connector. To read the flash codes, then short pins A and B (see figure 1).
If its a Simtec 56.0 or 56.1 fuel system (i.e. Ecotec engine) then you'll find a 10-pin ALDL connector. To read the flash codes you need to short pins A and B (see figure 1).
If its a Simtec 56.5 fuel system (i.e. Ecotec engine) then you'll find a 16-pin ALDL connector. To read the flash codes (P codes) you need to short out pins 5 and 6 (see figure 6).
Can I damage anything if I short the wrong pins?
Yes it is possible but unlikely, depending on what pin you short out. Most of them are 0v connections, but there are live +12v supply pins on there as well depending on which ALDL plug you have. If you are in doubt, don't do it! Double check the diagrams shown.
Where do I find the ALDL connector on the car?
Again if you have a Motronic or GM-Multec system, then these are commonly found in the engine bay or within the fuse box. Look for a 10-pin connector which is usually plugged into a blanking socket (i.e. not actually connected to anything). See figures 2, 3 and 5.
However if you have a Simtec 56.0 or 56.1 system, then the 10-pin ALDL connector can also be found in the engine bay or within the fuse box. See figures 2, 3 and 5.
However if you have a Simtec 56.5 system, then the 16-pin ALDL connector can be found in the fuse box area or under the trim to the hand brake or under the bulge in the carpet beside the passenger front seat. See figures 7 and 8.
General Notes:
Just before you start, make sure you note the following:
- If you don't have one, buy a Haynes manual for your car and have this is front of you if you find a fault and wish to investigate it.
- You'll need a paper clip and a pencil and paper to jot down the fault codes as they are flashed up.
- You do not need to start the engine but it doesn't hurt. Just switching on the electric's is enough (i.e. dash lights come on).
- If the paper clip is inserted in the wrong 2 pins, it is unlikely to damage anything, but double check you have the correct connections in the first place.
- For the ECU to log a fault, the ECU warning lamp on the dash usually has to be on for more than 30 seconds.
Step 1Locate the ALDL plug within your car. In this case it the 10-pin type can be found in the engine bay.
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Step 2With the connector pointing towards you and the retaining clip at the bottom, short the top two pins (A & B) on the left-hand side with the paper clip.
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Step 3Get in the car and switch on the engine. The ECU light will begin to flash and pause a number of times. Take a note of the flash patterns.
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