SRS warning light

On my 1998 MGF, I’ve been attempting to trace the cause of the SRS warning light being on. Using pscan, I get the error: 150B Front airbag circuit driver Short to ground.

From my understanding of auto-electrics, this is rather vague and I believe, from what I’ve read on various forums, that it can be caused by breakages in the rotary coupler and the ECU as well as damage to wiring insulation.

So far, I've replaced the connectors under the seats, both pre-tensioners and the rotary coupler. Next is the airbag ECU. That will be all of the components of the SRS system, so if the light is still on I don't know what I'll do!

When removing the old rotary coupler, I was excited to see strands of black plastic, which I assumed came from the internal tape—indicating that there was a breakage. But on dismantling the coupler, the tape is unbroken and a cream colour. I’m guessing that the strands were worn away from the edge of the coupler body, from 33 years of the steering wheel being turned.

I had two brainwaves: 1) Does the seatbelt need to be fastened when scanning for faults? To complete a circuit?

                                    2) Do I have to extinguish the warning light using pscan? What I mean is, does it being lit indicate historic errors—which I've since repaired? If so, how do I turn the light off?

I’m confused because watching MGLee’s excellent videos on YouTube, he replaced the rotary coupler, which made the warning light disappear!

SRS system do selftest after key in ignition barrel is turned on, but motor not started. Upon finishing selftest SRS light will come on with start of test and will lit until test is finished. Then light goes off. If during selftest fault is found, light will come on again, and fault written in the SRS ECU.

This means that light will not be lit if there is no error anymore, light will be lit only if fault is still present.

Error 1508 Front airbag circuit driver Short to ground means you have break in line to front airbag. I assume you have only drivers airbag. Then this means to me that you will need to inspect wires of SRS drivers airbag to SRS ECU for continuity and in accordance to fault registered one of these lines is most probably touching ground thus continuity test will not pass on that wire.

Have you tried to reset the codes and see if the light remains on?
Each ECU is different, for example I think on the Rover 75s that once the light is triggered it will not go out again even if the condition that caused it is rectified, until a tool is used to clear the codes.
Other ECUs require to be be power cycled a number of times (without a fault condition) before the light goes out.

On 1998 model SRS ECU will turn off the light if problem is solved on next power up selftest.

Devilheart, where did you find the under seat wire connectors? I have a bad connector in one of my F and would like to replace it. Thanks

Accessing the under-seat connectors involves kneeling beside your MGF, as if in prayer! Use a cushion or knee pads, as you'll be there for some time! A torch will help you see things. As built by the factory the connectors are attached to the frame of the seat by a black plastic clip, but this gets brittle with age and might not be there. The red block connector is in two halves—mine had a tiny amount of slack, so I replaced it with crimped on bullet connectors.

It's often stated on forums that the connector is the commonest cause of the warning light being illuminated, as it's shook about when the seat is adjusted backwards and forward. The previous owner of my 1998 MGF advised me that jiggling the connector would turn off the SRS warning light. It didn't. The wiring should be routed over the silver bar beneath the seat, to minimise disturbance, but it might well not be. Indeed, the wiring beneath the passenger seat of my car was crushed against the carpet beneath the lower frame rail; it looked like it had been that way for 33 years! As there's no airbag on the passenger side, I'm uncertain about whether faulty wiring could activate the light. I've received conflicting advice.

If you decide to remove the seats for easier access, you'll need a Torx socket bit size T50 + lots of patience, as the floor bolts are double the length they need to be. I've replaced both pre-tensioners for a cost of £10 apiece from eBay. Reconnecting the wiring beneath the seat is bothersome, as the wire insulation are different colours—you might think that like would connect to like, but on my car (from memory) Blue/Red connects to Blue/Brown. I read somewhere that making a wrong connection could set off the explosive charge in the pre-tensioner!

Good luck with your block connector(s)...you could be one of those owners for whom a quick jiggle does the job!