Inevitably, at some point in a car's life, something will go wrong with it. If the car has been manufactured from about 1994 onwards, faults relating to the fuelling and ignition system may be warned of by the engine's control unit, or ECU, by illumination of a warning light on the dashboard or instrument display. This light usually has an engine symbol with a lightning bolt going through it, or something similar.

To find out what this warning light means, one might take the car to a garage, where it would be connected to a computer which would read out what the fault is, at a needless cost to the vehicle owner. I have known this five-minute procedure to cost as much as £30 GBP (about $60 USD), when it can be done (depending on the exact vehicle) by oneself for nothing, in just as little time.

This will tell you how to read fault codes on several Vauxhall/Opel/Holden vehicles. For simplicity's sake, I will refer to them by their Vauxhall (i.e. British) names only, since there is some conflicts with the Opel names (for example the Vauxhall Cavalier was sold as the Vectra in Europe, which is also the name of the followup to the Cavalier in Britain). This covers the Cavalier, Calibra, Vectra, Astra (Mk2/3), Carlton, Senator, and the Omega (at least up to 1999, unsure after that). Note that diesel models are not covered.

All that is required for any of these procedures is:

It is also useful to know whether the engine of the car is an Ecotec. This is simple to determine: just look at the spark plug cover in the engine bay; if it has 'Ecotec' on it in large letters, then it is an Ecotec (natch). If you don't know what the spark plug cover is, then you might want to leave this to a garage as the results of this will probably be meaningless to you. If you insist, open the bonnet/hood and see if you can see the word 'Ecotec' in big letters somewhere under there.

This procedure will differ in minor ways depending on the car - I will group them into categories for simplicity:

  • Group A: The Cavalier, Carlton, Senator and Calibra.
  • Group B: The Astra and Omega.
  • Group C: The Vectra.

First, locate the diagnostic plug. This is the plug that would be connected to the diagnostic machine, had you taken the car to a garage. In group A cars it is in the engine bay in the rear right hand corner (it is clipped into a small holder), if at the front of the car looking back. Group B cars have it in the in-car fusebox. On group C cars it is under a detachable half-moon-shaped cover, under the handbrake handle.

Next, get the plug/connector the right way up so you know which pins are which. All of them have a irregularity of some kind on one side (usually a stud, or clip), so this is easy enough. Group A, the stud should be on the bottom. Group B, the stud should be on the right. Group C, the protrusions on one side of the plug should be on the left. The different plugs all have between 10 and 16 pins. On group A cars they go from A to K, from top to bottom clockwise, thus:

-------------
| A B C D E |
| K J H G F |
-------------
     ||

On the Astra they go from A to K from top right to top left clockwise, thus:

 ------
/ K A |
| J B |
| H C ||
| G D |
\ F E |
 ------

On the Omega and Vectra they go from 1 to 16 from the top left to bottom right, thus:

    -\---------
 __/  \        \
|__  1 \_   8   \
 __|     \      |
|__  9    \ 16  /
   \       \   /
    --------\--

Now, if the engine is an Ecotec, start it up. Otherwise, just turn the ignition on (although this will still work if you start the engine). The next step involves shorting two of these pins together, using the aforementioned piece of wire (However before you do this I recommend you read the next paragraph). Cars in group A & the Astra, short pins A & B. Group C cars and the Omega, short pins 5 & 6.

In suitably-specified cars (cars with certain engines or those manufactured after a certain date will not respond to this technique, and will require either a garage, or a suitable device bought from somewhere like Halfords to read off the fault codes), the engine management light will flash according to the fault codes it has stored in its memory. These take the form of a sequence of flashes for each number, followed by a pause, followed by the next number, followed by a long pause, followed by the next number in the same manner.

For example, when the light first begins flashing, it flashes the code '12' three times as a marker. The code '12' takes the form of one flash, a pause, then two flashes. After a longer pause, the code will flash again two more times. All the codes are output in this fashion. If the only code output is code '12', then no fault codes are stored (code '12' is used to indicate the beginning and end of the fault code list). All codes are flashed three times.

Whilst this is a digression, to avoid unnecessary worry, it should be noted that if the fault codes are read without the engine running, the ECU will probably report a fault code for an absent RPM signal - this is simply because the engine is not running and no cause for concern.

As an aside, to clear the ECU's list of fault codes (which would also cost extra money, at a garage), turn the ignition on and off 25 times (this has the effect of 'pushing' the stored fault codes off the memory stack of the ECU). Alternatively, disconnect the battery or the ECU connector plug for about 30 minutes or so. Note that this will also reset the ECU parameters to their defaults (there is a limited 'learning' facility in the ECUs which adapts certain parameters such as ignition timing, to the way the car is driven) - it will take about 200 miles of driving for them to adapt again.(1) This clearing technique, as with the code reading technique, may not work for newer vehicles. On such vehicles the codes can only be cleared by a suitably-equipped garage.

Further, on certain vehicles (those in group A, to my knowledge), it is possible to view fault codes from other ECUs in the vehicle - for example (where fitted), those for the ABS (Anti-Lock Braking) system, the vehicle security system, the Traction Control system, the 4x4 system and the automatic gearbox. The full pin-out for the diagnostic plug on type A vehicles is as follows:

  • A - Ground
  • B - Engine ECU
  • C - Automatic Gearbox (except models with traction control)
  • D - Fuel Computer (not UK models)
  • E - Engine ECU
  • F - +12v (fused)
  • G - Bi directional data line
  • H - Alarm
  • J - 4x4 or Traction Control (pin may not be present on certain models)
  • K - ABS

Simply short the pin for the desired system to ground, and if capable, the appropriate ECU will flash any fault codes on its dashboard light - for example, short pins A & K for the ABS fault codes, and the ABS warning light will flash with any ABS fault codes. Note that the engine ECU can be read on pin E as well as pin B. Do not short pins A & F (12v+ to ground); it won't do anything except blow fuse 8 (therefore hopefully avoiding component damage) and you could burn yourself on the wire, as I did.

Now you know how to read fault codes, you will probably find a list of these fault codes and their meaning useful. Read from one of the following tables depending which make of ECU the vehicle has.

Bosch Motronic fault code listing

This covers Motronic version 2.5 and 2.8 ECUs, fitted in Vauxhall/Opel vehicles from approximately 1990 onwards, which control fuel and ignition systems. Fault codes are shown with the corresponding fault. Fault codes in related, electronically-controlled vehicle systems such as ABS, Traction Control, and 4x4. This mainly pertains to the Vauxhall Cavalier, Carlton (Vectra-A and Omega-A in Europe, respectively), Senator, and Calibra.

Engine ECU
12 Diagnosis initiation/separator (indicates beginning/end of fault code list)
13 Oxygen sensor - open circuit
14 Coolant temperature sensor - voltage low
15 Coolant temperature sensor - voltage high
16 Knock signal circuit - no voltage change
17 Knock signal circuit 2 - no voltage change (V6 models only)
18 Knock control module (ECU)
19 Incorrect RPM signal (Crankshaft sensor - incorrect signal)
21 Throttle position sensor - voltage high
22 Throttle position sensor - voltage low
23 Knock sensor - out of range
24 Speed sensor (MPH)
25 Injector 1 - voltage high
26 Injector 2 - voltage high
27 Injector 3 - voltage high
28 Injector 4 - voltage high
29 Injector 5 - voltage high/ Fuel pump relay voltage low (non-V6 models)
30 Injector 6 - voltage high (V6 models only)
31 No engine RPM signal (engine not running, or no Crankshaft sensor signal)
32 Fuel pump relay - voltage high
33 MAP sensor - voltage high
34 MAP sensor - voltage low
35 Idle air control valve stepper motor (no idle speed control)
38 Oxygen sensor - voltage low (weak mixture)
39 Oxygen sensor - voltage high (rich mixture)
41 1 gear indent switch - voltage low
42 1 gear indent switch - voltage high
43 EGR system
44 Oxygen circuit - voltage low (weak mixture)
45 Oxygen circuit - voltage high (rich mixture)
47 Linear EGR position
48 Battery - voltage low
49 Battery - voltage high
51 ECU memory failure
52 Check engine light - voltage high
53 Fuel pump relay - voltage low
54 Fuel pump relay - voltage high
55 ECU faulty
56 Idle air control valve - voltage low/high
57 Idle air control valve - voltage high/low
61 Fuel tank vent valve - voltage low
62 Fuel tank vent valve - voltage high
63 EST line coil cylinders 2 & 3 - voltage low
64 EST line coil cylinders 1 & 4 - voltage low
65 Idle CO potentiometer - voltage low
66 Idle CO potentiometer - voltage high
67 Idle position switch - voltage low (idle position switch not opening)
69 Intake air temperature sensor - voltage low
71 Intake air temperature sensor - voltage high
72 Full position switch - voltage high
73 Air flow sensor - voltage low
74 Air flow sensor -voltage high
75 Torque control - voltage low
76 Torque control - continuous
79 Full load inhibitor - voltage low (traction control signal)
81 Injector valve 1 - voltage low
82 Injector valve 2 - voltage low
83 Injector valve 3 - voltage low
84 Injector valve 4 - voltage low
85 Injector valve 5 - voltage low (V6 models only)
86 Injector valve 6 - voltage low (V6 models only)
87 A/C cut-off relay - voltage low
88 A/C cut-off relay - voltage high
92 Camshaft sensor failure
93 Hall sensor - voltage low
94 Hall sensor - voltage high
95 Hot start valve - voltage low
96 Hot start valve - voltage high
97 Ignition/Injection cut off - voltage high (traction control signal)
113 Boost control out of range (turbo models only)
114 Boost pressure (idle) above upper limit (turbo models only)
115 Boost pressure (full) below upper limit (turbo models only)
116 Boost pressure (full above upper limit (turbo models only)
117 Wastegate valve - voltage low (turbo models only)
118 Wastegate valve - voltage high (turbo models only)
Anti-Lock Braking System ECU
16 Left-front solenoid
17 Right-front solenoid
18 Rear solenoids
19 Solenoids relay circuits
25 Faulty sensor toothed ring
35 Pump relay circuits (hydraulic modulator)
37 Stop lamp switch (brake pedal switch)
39/44 Left front RPM sensor (air gap between sensor and toothed ring, & sensor operation)
41/45 Left front RPM sensor (resistance & connections)
42/46 Right front RPM sensor (air gap between sensor and toothed ring, & sensor operation)
43/47 Right front RPM sensor (resistance & connections)
48 System voltage wrong (alternator or battery)
55 Faulty ECU
Four-wheel drive ECU
15 Oil temperature sensor - voltage high
24 No speed signal
31 No engine RPM signal
32 Pressure switch faulty
33 Solenoid valve - voltage high/transfer box overheated to 160°C on 1992 models
34 Solenoid valve - voltage low
37 Brake lamp switch
39 No ABS signal, or 0MPH and 2300RPM for more than 15 seconds
55 ECU faulty
71 Brake switch - voltage high
72 Brake switch - voltage low
73 Car stopped without braking from over 37mph
74 Power Assisted Steering PAS pressure less than 10 bar
75 Oil temperature sensor - voltage low/transfer box overheated to 160°C or 140°C for over 118MPH.
(Note that codes 15,39,71-75 apply only to models from roughly 1994 onwards, with electronic speedometers)
Traction Control ECU (V6 models and Astra GSi only)
14 Coolant temperature sensor - voltage low
15 Coolant temperature sensor - voltage high
21 Throttle position sensor - voltage high
22 Throttle position sensor - voltage low
26 Traction control throttle position sensor - voltage high (throttle motor resistor failure; V6 models only)
27 Traction control throttle position sensor - voltage low (throttle motor resistor failure; V6 models only)
31 No engine RPM signal
37 Stop lamp switch (brake pedal switch)
39 Left front RPM sensor (ABS fault)
42 Right front RPM sensor (ABS fault)
44 Left rear RPM sensor (ABS fault)
46 Right rear RPM sensor (ABS fault)
55 ECU fault
57 ABS status - signal low (indicates ABS system fault, not TC system fault)
58 ABS status - open circuit
63 Throttle motor - open circuit
64 Throttle motor - short circuit
82 On/off switch voltage low (dashboard switch)
Alarm ECU (Factory fitted alarms only)
18 Fault with disarm signal 
25 Horn - Voltage Low (Horn O/C or fuse blown)
26 Indicator left - open circuit
27 Indicator right - open circuit
28 Ultrasonic sensor driver side - open circuit or incorrect voltage
29 Ultrasonic sensor passenger side - open circuit or incorrect voltage
32 Boot (trunk) sensor caused an alarm condition
33 Bonnet (hood) sensor caused an alarm condition
34 Doors caused an alarm condition
35 Ignition turned on caused an alarm condition
36 Immobilization circuit - open circuit (starter circuit triggered causing alarm)
37 Radio caused an alarm condition
38 Ultrasonics caused an alarm condition
39 Fault with disarm signal. (central locking fuse blown, causing alarm condition)
40 Two alarm triggers at the same time.
41 Spare alarm input caused alarm condition
46 Rear Window smashed caused an alarm condition  ('92 onwards models only)
52 Horn Voltage Low - Horn O/C or fuse blown
55 ECU fault
Automatic Gearbox ECU
17 Solenoid 1-2/3-4 - voltage low
21 Throttle position sensor - voltage high
22 Throttle position sensor - voltage low
23 Coolant temperature switch - voltage high
25 Solenoid 1-2/3-4 - voltage high
26 Solenoid 2-3 - voltage low
27 Connection solenoid 2-3/solenoid TCC
28 Solenoid 2-3 - voltage high
29 TCC Solenoid - voltage low
31 No engine RPM signal
32 Pressure regulator solenoid - voltage low
33 Pressure regulator solenoid - current high
36 TCC Solenoid - voltage high
38 No transmission input RPM signal
39 No transmission output RPM signal
41 Gear error - hydraulic fault
42 Pressure regulator solenoid - short circuit
47 Down shift protection fault
48 Battery - voltage low
49 Battery - voltage high
56 Selector switch - incorrect signal
65 AT oil temperature sensor - voltage high
66 AT oil temperature sensor - voltage low/high
67 AT oil temperature sensor - voltage high
75 Transmission switch - voltage low
76 Engine TPS load signal incorrect
77 Kickdown switch - voltage low
78 AT shift time - too long

Simtec 56 Fault code listing

Models from about 1995-1996 on will probably use codes from this list.

13 Oxygen Sensor - open circuit
14 Coolant temperature sensor - voltage low
15 Coolant temperature sensor - voltage high
16 Knock sensor signal circuit
19 Incorrect RPM signal
21 Throttle position sensor - voltage high
22 Throttle position sensor - voltage low
23 Knock signal - out of range
24 No vehicle speed signal
25/26/27/28/29/30 Injector valve 1/2/3/4/5/6 - voltage high (injector(s) short-circuited to battery, or injection signal not present)
37 Check light - voltage low
38 Oxygen sensor circuit - voltage high
39 Oxygen sensor circuit - voltage low
44 Oxygen sensor - lean exhaust
45 Oxygen sensor - rich exhaust
48 Battery - voltage low
49 Battery - voltage high
52 Fuel pump relay - voltage low
53 Fuel pump relay - voltage high
54 Fuel pump relay 0 - voltage high
55 ECU memory fault
56 Idle air control valve - voltage high
57 Idle air control valve - voltage low
61 Fuel tank vent valve - voltage low
62 Fuel tank vent valve - voltage high
69 Intake air temperature
71 as above
73 Mass air flow temperature
74 Mass air flow temperature
75 Torque control - voltage low
76 Torque control - continuous
81/82/83/84/85/86 - Injector valve 1/2/3/4/5/6 - voltage low (injector(s) short  circuit to ground)
87 A/C cut-off relay - voltage low
88 A/C cut-off relay - voltage high
91 Oxygen heating - voltage high
92 Camshaft position sensor - incorrect signal
93 Camshaft position sensor - voltage low
94 Camshaft position sensor - voltage high
95 Hot start valve - voltage low
96 Hot start valve - voltage low
97 Traction control module - incorrect signal
98 Oxygen Sensor heating - voltage low
113 Turbo wastegate control - boost pressure high
114 Turbo boost pressure (idle) - above upper limit
115 Turbo boost pressure (full) - below upper limit
116 Turbo boost pressure - above upper limit
117 Turbo wastegate regulating valve - voltage low
118 Turbo wastegate regulating valve - voltage high
119 Manifold absolute pressure (MAP) sensor - range or performance
121 Oxygen sensor - lean mixture
122 Oxygen sensor - rich mixture
123 Intake manifold air control solenoid (1) - blocked
124 Intake manifold air control solenoid (2) - blocked
125 MAP sensor - below upper limit
126 MAP sensor - above upper limit
129 Exhaust gas recirculation (EGR) system - voltage low
131 EGR system - voltage high
132 EGR system - incorrect signal
133 EGR system (2) - voltage high/low (unclear)
134 EGR system (2) - voltage low/high (unclear)
135 Malfunction indicator lamp - voltage low
136 ECU memory fault
137 ECU - temperature high
138 MAP sensor - voltage low
139 MAP sensor - voltage high
143 Immobiliser - no signal/wrong signal
144 Immobiliser - no signal
145 Immobiliser - wrong signal

Simtec 56.5 Fault Code Listing

If someone could contribute some extra meaning to this section I'd be grateful, as the source is not very comprehensive.

0100 Mass air flow sensor
0105 Intake manifold pressure sensor
0110 Intake air temperature sensor
0115 Intake coolant temperature sensor
0120 HEGO heater
0150 HEGO
0173 HEGO
0201/020/0203/0204/0205/0206 Injector 1/2/3/4/5/6
0230 Fuel pump
0325 Knock sensor
0330 Knock sensor 2
0335 Crank sensor
0340 Camshaft sensor
0351 Ignition coil 1+4
0352 Ignition coil 2+3
0400 EGR valve
0403 EGR valve
0410 Secondary air pump relay
0412 Secondary solenoid valve
0433 Fuel tank vent valve
0500 Odometer frequency sensor
0505 Idle speed stepper motor/idle air regulator
0560 Battery
1110 Switch over valve solenoid
1112 Switch over valve 1
1113 Switch over valve 2
1120 Throttle body malfunction
1229 Power supply relay
1231 Fuel pump relay
1320/1327/1328/1329 Knock control cylinder 1/2/3/4
1405 EGR valve
1410 Secondary air pump relay
1411 Secondary air pump
1501/1502/1503 Immobiliser control unit
1530 Air flow relay
1600 Internal control module
1601 ECU temperature high
1602 Knock control module
1604/1605/1606 Knock control unit
1640 Knock control unit or quad drive module
1690 MIL/Engine fail (malfunction indicator lamp)
1740 Torque control unit

These instructions worked fine for me. It's not my fault if you hurt yourself or damage your car following them.

Sources:
  • akirwan.freeserve.co.uk
  • www.cavweb-forums.co.uk
  • www.vauxweb.com
  • A good friend of mine who owns a garage and first pointed this 'trick' out to me.

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