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ECU Fault Codes

DISCLAIMER: The information in these documents are a collection from experience (friends or myself), magazine articles, mailing

lists and Internet web sites etc. So don't take these as 100% correct gospel, hence I don't take any responsibility for any of these

guides.

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Created: 19 Dec 2001

Updated: 5 Aug 2002

Revision 6

Click on a picture for a

bigger view

What are 'fault codes'?

Figure 1

10-pin ALDL Test Plug

connections.

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?

Figure 2

Location of the 10-pin

ALDL plug in a Nova

engine bay.

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.

Figure 3

Close up of the 10-pin

ALDL plug in a Nova

engine bay.

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.

Figure 4

ECU warning lamp on the

dash board.

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 ).

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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 ).

Figure 5

Location of 10-pin ALDL

Test Plug in a Calibra.

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?

Figure 6

Location of 10-pin ALDL

Test Plug in an Astra-F.

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 .

Figure 7

16-pin ALDL Test Plug

connections.

Figure 8

Location of 16-pin ALDL

Test Plug in Astra MK4

within Fuse Box.

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.

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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.

OK, got all the above? Then follow the steps below (remember to click on the pics for a bigger view):

Step 1

Step 2

Step 3

Locate the ALDL plug within

your car. In this case it the 10-

pin type can be found in the

engine bay.

With 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.

Get 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.

How to read Motronic or GM-Multec Flash Codes:

The Motronic or GM-Multec fuel systems use a 2 digit flash code. The engine does not have to be

running when reading the codes, although it doesn't hurt if it is.

Once the wire link is in place and the electric's are on, the ECU warning lamp will begin to flash out

the codes (wait for the initial boot up check that lights up all the warning lamps). Each fault code is

repeated 3 times and then it moves onto the next one (if any). Once at the end of the logged fault

code list, it will go to the beginning again, giving you plenty of time to note down the code (on each

fault code shown, there will be a pause before it shows the next one). It will carry on like this forever

until you remove the key from the ignition or the battery runs flat. To clear the fault codes, simply

remove the battery leads for a few minutes and then reconnect.

For example, lets say there was a ECU warning lamp noted and the owner wanted to read what

fault code was logged. The owner has already put the wire link in place and switched on the ignition.

A flash is indicated by an astrix (*) and a pause is shown as a dash (-).

*-** (1 flash, 1 pause and another 2 flashes = code 12)

*-** (12)

**-*** (23)

*-** (12)

**-*** (23)

*-** (12)

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Owner then takes the key out of the ignition.

Lets go through what has happened. After switching on the ignition, the dash board lights up

showing the self check, after that all the lights go out and the ECU warning light begins to flash the

error code. The first code is 12 (one flash, a pause and then two flashes). This is repeated 3 times.

Code 12 at this moment means initiation of diagnosis. After that came code 23, which means 'Knock

control module', i.e. there is most likely a faulty unit or a bad connection at its plug. After code 23

has been repeated 3 times it flashes a separator code, which is code 12.

It flashes this 3 times before going to the next fault code. The next code is code 23 again which

means its finished showing the logged fault codes and has started back at the beginning. The owner

can switch off the ignition. A healthy car should display a stream of code 12's. To find out what fuel

system you have, read the "Fault Code Chart" below.

How to read Simtec 56.0/56.1 Flash Codes:

The Simtec 56.0/56.1 fuel systems use a 2 digit flash code. The engine ideally needs to be running

when reading the fault codes, otherwise it may show incorrect fault codes.

Once the wire link is in place and the engine is running, the ECU warning lamp will begin to flash out

the codes (wait for the initial boot up check that lights up all the warning lamps). Each fault code is

repeated 3 times and then it moves onto the next one (if any). Once at the end of the logged fault

code list, it will go to the beginning again, giving you plenty of time to note down the code (on each

fault code shown, there will be a pause before it shows the next one). It will carry on like this for ever

until you remove the key from the ignition or the battery runs flat. To clear the codes simply turn on

and off the ignition 30 times with a 5 second 'on' gap in-between (time allowed for self check to

finish).

For example, lets say there was a ECU warning lamp noted and the owner wanted to read what

fault code was logged. The owner has already put the wire link in place and switched on the ignition.

A flash is indicated by an astrix (*) and a pause is shown as a dash (-).

*-** (1 flash, 1 pause and another 2 flashes = code 12)

*-** (12)

**-*** (23)

*-** (12)

**-*** (23)

*-** (12)

Owner then takes the key out of the ignition.

Lets go through what has happened. After switching on the ignition, the dash board lights up

showing the self check, after that all the lights go out and the ECU warning light begins to flash the

error code. The first code is 12 (one flash, a pause and then two flashes). This is repeated 3 times.

Code 12 at this moment means initiation of diagnosis. After that came code 23, which means 'Knock

control module', i.e. there is most likely a faulty unit or a bad connection at its plug. After code 23

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has been repeated 3 times it flashes a separator code, which is code 12.

It flashes this 3 times before going to the next fault code. The next code is code 23 again which

means its finished showing the logged fault codes and has started back at the beginning. The owner

can switch off the ignition. A healthy car should display a stream of code 12's (note: some ECU

systems will also show code 31 or 19 because it doesn't see the engine turning over, this is not a

fault because you haven't started the car). Simply start the car and read the fault codes again. To

find out what fuel system you have, read the "Fault Code Chart" below.

How to read Simtec 56.5 Flash Codes (P Codes):

The Simtec 56.5 fuel systems use a 4 digit flash code. The engine ideally needs to be running when

reading the fault codes, otherwise it may show incorrect fault codes.

Once the wire link is in place and the engine is running, the ECU warning lamp will begin to flash out

the codes (wait for the initial boot up check that lights up all the warning lamps). Each fault code is

repeated 3 times and then it moves onto the next one (if any). Once at the end of the logged fault

code list, it will go to the beginning again, giving you plenty of time to note down the code (on each

fault code shown, there will be a pause before it shows the next one). It will carry on like this for ever

until you remove the key from the ignition or the battery runs flat. To clear the codes simply turn on

and off the ignition 30 times with a 5 second 'on' gap in-between (time allowed for self check to

finish).

For example, lets say there was a ECU warning lamp noted and the owner wanted to read what

fault code was logged. The owner has already put the wire link in place and switched on the ignition.

A flash is indicated by an astrix (*) and a pause is shown as a dash (-).

Note that 10 flashes = number 0.

**********-*-*-***** (10 flashs, 1 pause, 1 flash, 1 pause , 1 flash, 1 pause and 5 flashes = P code

0115)

**********-*-*-***** (0115)

**********-***-***-********** (0330)

**********-*-*-***** (0115)

**********-***-***-********** (0330)

Owner then takes the key out of the ignition.

Lets go through what has happened. After switching on the ignition, the dash board lights up

showing the self check, after that all the lights go out and the ECU warning light begins to flash the

error code. There is no initiation flash code, the ECU will flash out the fault codes straight away. This

is repeated 3 times.

P code 0115 means 'Intake manifold pressure sensor', i.e. there is most likely a faulty unit or a bad

connection at its plug. It flashes this 3 times before going to the next fault code. Remember to show

a 0 number it flashes the ECU warning lamp 10 times.

The next code is code 0330 which means 'Knock sensor 2' which suggests the engine has two

knock sensors on it, hence the 2nd one is faulty or has bad connections. Again this flashes the

same fault P code 3 times before moving onto the next. In this case it there are no more faults and

the P codes repeat themselves.

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