Srs

As some of you know, I've been living with this problem for months. Occasionally it gets on my tits and I have another go at it but so far have had no success.

SRS warning in dash is on along with message display ÄIRBAG FAULT". Now what's interesting is that the red SRS indicator is usually steady but occasionally pulses bright and dim (not on and off). I wonder if this means something and whether I should count the pulses? I remember on very early OBD compliant cars you could count the flashes, refer to a chart and determine the fault code. It seems a bit daft they would have kept that what with the info display and Testbook etc etc. Maybe its just a quick and dirty way to tell you that both bulbs work and that's all?

What have I done: Unplugged and replugged the rotary coupler and passenger airbag (no sidebags). Visually inspected connection to external crash sensors. Tried every brand of diagnostics out there but none can communicate with the SRS ECU - link error is all they say. Changed the female OBD connecter in the car - found myself with an extra wire that despite Wammers' and Datatek's valiant efforts we could not identify with 100% certainty. Pin 13 or 14 is the SRS out, my car is export model apparently further fettled by SVU so don't really know which it should be; have tried swapping them and stuff but still no luck.

I'm down to suspecting:

1. SRS-ECU is dead
2. Break in data connection between ECU and OBD.
3. Problem is still with OBD connecter.

What do better minds suggest? Any way to test the ECU on its own? I don't have access to a donor vehicle I could swap one out of to try. If I do get it out and try to do a continuity test between Pin 14 in OBD and the ECU connecter, which pin should I look at there?

Really hoping someone with a fresh perspective will spot something obvious I've missed as I'm circling the drain here!

I forgot to mention how the problem started. The car was laid up for over a month and its apparently documented that if the battery drains completely sometimes an airbag fault is stored. Only wants a simple reset, problem is without the data-link...

Don't remember that one Rash. If you look at diagrams it should be easy enough to identify the wire. Or did we go down that road?

The pulsing is due to the airbag light having two bulbs in case one breaks. It should be pulsing constantly so that's something you should have a look at.

jacckk said:

The pulsing is due to the airbag light having two bulbs in case one breaks. It should be pulsing constantly so that's something you should have a look at.

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The SRS light should not be pulsing in normal operation. If one of the two bulbs fails the other one will come on and not go out until the other is replaced. Maybe the pulsing is an indication of a bulb fail. But i can find no reference to this in RAVE. Pulsing or flickering bulbs are more commonly associated with alternator charge switching at low RPMs.

I've seen two cars do it.

As rasheed said its not on and off more of a brighter and dimmer where one light is constantly on and another flashes on and off.

jacckk said:

I've seen two cars do it.

As rasheed said its not on and off more of a brighter and dimmer where one light is constantly on and another flashes on and off.

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I've just explained that. There are two bulbs, as far as i am aware they do not both light at the same time, one is a backup. They are separately powered from the ECU. If one fails the other stays on all the time. But there is no reference to them in RAVE. So all is supposition.

Low battery, alternator or bad earths might cause flashing. The only way forward is fix the data link and diagnostics. However, it may be that the reason that you cannot communicate is a dead ECU, they are cheap enough on Ebay.

Have plugged in diagnotics I had the srs light come up last week plugged in nano left seat side airbag gave the yellow wire a wiggle recycled the ignition gone .

Question - If the ECU were dead, would the SRS light be on or the dash display "Airbag Fault"? In other words, having this displayed I would take as meaning the ECU is working unless we know the fault's also stored in the BECM or the trip computer? Because I have checked and there are no uncleared faults in BECM (can't diagnose trip computer afaik).

Wammers if you've a diagram of the ECU connector to hand I'd be much obliged if you could post it.

Jacckx I tend to agree that the pulsing is proof that both bulbs work. I think its just to tell you don't bother having the binnacle out, look elsewhere. However its not constant as you suggest. Lamp is usually steady then pulses for about 30 seconds, goes back to steady for the next hour or so. I haven't actually timed the gap between episodes. Its either on a timer or some condition or the other manifests for a while and then goes back.

Data the pulsing isn't erratic or RPM related. Its too evenly timed, definitely a signal of some kind.

Grit glad you solved it. In your case its a known kink in P38s having seat-mounted side bags that the cable can get stretched and loose connector caused sometimes even simply by moving the seat back or forth.

rasheed said:

Question - If the ECU were dead, would the SRS light be on or the dash display "Airbag Fault"? In other words, having this displayed I would take as meaning the ECU is working unless we know the fault also stored in the BECM or the trip computer? Because I have checked and there are no uncleared faults in BECM (can't diagnose trip computer afaik).

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Un plug the battery disconnect it and you will have your answer doh

rasheed said:

Question - If the ECU were dead, would the SRS light be on or the dash display "Airbag Fault"? In other words, having this displayed I would take as meaning the ECU is working unless we know the fault also stored in the BECM or the trip computer? Because I have checked and there are no uncleared faults in BECM (can't diagnose trip computer afaik).

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Think you can take that the ECU is working if you have lamp and "Air bag fault" on display. I am more interested as to why you cannot access ECU with diagnostics. What year is your car. What diag are you using? There are two different SRS systems type 1 and type 2. Nanocom will read both other diag may only read one. And that is why you cannot communicate with the ECU.

I have the earlier with the outboard crash sensors (behind each of headlamp). The later one has a single sensor housed within the ECU casing. In any case my own diag is Hawkeye and it is able to read both. I've also taken it to the dealer to try their Testbook T4 and to a high-end indy with Autologic. No one around here has Rovacom or Nano or whatever its called now. The Autologic by the way is a superb piece of kit, does even more than Testbook. But is pricey!

I am leaning more and more towards a continuity fault I think.

rasheed said:

I have the earlier with the outboard crash sensors (behind each of headlamp). The later one has a single sensor housed within the ECU casing. In any case my own diag is Hawkeye and it is able to read both. I've also taken it to the dealer to try their Testbook T4 and to a high-end indy with Autologic. No one around here has Rovacom or Nano or whatever its called now. The Autologic by the way is a superb piece of kit, does even more than Testbook. But is pricey!

I am leaning more and more towards a continuity fault I think.

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I have a spare one of those ECU's. It's perfectly possible for the ECU coms to fail and for the message to display, the SRS ECU doesn't generate the message as such, that is held in memory in the dash, it just signals the need to display the message with a single line changing state, therefore a dead ECU may well cause the message to display. I'm not saying that is your problem, I'd go for the comms wiring first to the OBD connector. It's all in RAVE.

Keith I'll be back in Germany around Christmas, can you hold on to your spare till then? I might take it off your hands if no other solution in the meantime. Cheers.

rasheed said:

Keith I'll be back in Germany around Christmas, can you hold on to your spare till then? I might take it off your hands if no other solution in the meantime. Cheers.

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No problem Rash.