P38 SRS/Airbag Fault

I have a 1997 (P registration) P38 4.6 V8 GEMS. Recently the red SRS lamp on the dash is continually on with the 'Airbag Fault' message in the digital display.

Nanocom is ‘unable to communicate with ECU’ but functions on everything else on the car. I have tried it on all three Airbag options on the Nanocom menu.

So far I have done the following:

• Checked continuity between OBDII and DCU and all found to be okay. This isn’t surprising as the OBDII and ALL terminals within it were recently renewed with new due to corrosion issues.
• Checked continuity through rotary coupler on steering wheel to red plug under dash and all okay
• No continuity done on any other yellow sheathed loom due to specific advice on forums not to.
• Checked both bulbs in cluster and both are okay
• Airbag DCU under rear of centre console replaced with a tested second-hand working one of the same type
• Battery was iffy when problem first started appearing but since changed with the one off my daily driver which is known to be good.

The car has no side airbags or crash sensors next to headlamps.

I understand that on these earlier cars any correction in the circuit does not generate an automatic reset which has to be done through the diagnostic reader (i.e. Nanocom) but cannot do this as outlined above.

The only other thing which does not seem right, but has been like this since I have owned the car (5 years) as I have never had it to bits, is the red plug connecting the passenger airbag has blue to white on both terminals, rather than blue to blue and white to white. They cannot be swapped over due to the red plug only going together one way.

Any advice would be appreciated.

What voltage do you have on the battery that "is known to be good"?
If you have swapped the ECU and the has no side airbags, you are left with connection problems, maybe a broken wire.

Thanks. I've got 12.8 volts on the good battery.
When I've gone out to work on it tonight there is no SRS lamp or Airbag fault showing. Even with key in position 2 the bulb check isn't working (complete opposite to yesterday). Bulbs are okay as I've checked them with a multimeter and switched then with the oil and seatbelt ones which are working. Nanocom still won't connect.
I did leave the passenger size plug disconnected last night as well as the battery.
What checks can I do on the ABS loom to find a possible broken wire as I understand from other posts it should not be checked using a multimeter?
Cheers.

Westmoreland Rover said:

Thanks. I've got 12.8 volts on the good battery.
When I've gone out to work on it tonight there is no SRS lamp or Airbag fault showing. Even with key in position 2 the bulb check isn't working (complete opposite to yesterday). Bulbs are okay as I've checked them with a multimeter and switched then with the oil and seatbelt ones which are working. Nanocom still won't connect.
I did leave the passenger size plug disconnected last night as well as the battery.
What checks can I do on the ABS loom to find a possible broken wire as I understand from other posts it should not be checked using a multimeter?
Cheers.

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With the ECU and airbags unplugged, you can safely do end to end continuity checks on the loom.
Silly question, I suppose the fuses have been checked?

Thanks Datatek.
I will check them over the weekend with everything unplugged. Yes fuses are all okay, those being the first things I looked at.

Westmoreland Rover said:

Thanks Datatek.
I will check them over the weekend with everything unplugged. Yes fuses are all okay, those being the first things I looked at.

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Don't forget to check the earth points, memory is bad but I think there is one under the drivers seat at the back of the BECM.

Datatek said:

Don't forget to check the earth points, memory is bad but I think there is one under the drivers seat at the back of the BECM.

Click to expand...

There is.

Mark Piercy said:

There is.

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Merci

Datatek said:

Merci

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Bah de rien