mashbury

Hi I'm new to Mercs and trying to dignose an SRS airbag problem. Car's a UK Spec 1993 300TD.

The symptom is that, at switch on, the SRS light comes on for about 4-5 seconds, then goes out,which is correct behaviour, but then comes on again permanently after about 25 seconds.

I've learned about the l.e.d. blink method of determining the fault codes. I have an 8-pin diagnostic connector on the driver-side firewall near to the fuse-box. Pin 6 seems to be the SRS light. Connecting the l.e.d. to this pin, feeding it with +12V via a resistor and shorting pin 6 to chassis for around 2 seconds makes the l.e.d. blink twice.

I reckon this means I have a fault code of 2.

My question is, what does this mean? Does anyone out there have the list of fault codes and what hardware faults they relate to?

I'd be grateful for help on this. Like someone else on the forum said, paying £80 per hour + VAT for the dealer to say " hmm could be tricky, we'd need the car for a couple of days.." is giving a blank cheque & not something I want to do!!

Any other tips on SRS system would be welcome, and how to clear the codes.

I'd be happy to give details of the blinker if anyone is interested (it's pretty simple!)

Thanks in advance for any help

Peter

echo200

I’m probably the ‘someone else’ you are referring to!

From a list of codes for a U.S. spec. E320-124, sent to me by a helpful reader, unless the codes only relate to U.S. specs., the code number you describe refers to the oxygen sensor.

Incidentally, I’ve just had a full analogue diagnostic authorised by Daimler/Chrysler UK, to be performed next week by my local MB dealer.

echo200

DTC/ Malfunction

1/ No malfunctions stored in memory from systems monitored.
2/ Oxygen sensor
3/ Lambda control
4/ Secondary air injection (system function)
5/ EGR (system function)
6/ Idle speed control (ISC)
7/ Ignition system defect
8/ Engine coolant temperature sensor
9/ Intake air temperature sensor
10/ Hot film mass airflow sensor
11/ TN-signal
12/ Oxygen sensor heating
13-14/ Not used
15/ Wide open throttle (WOT) function
16/ Closed throttle position (CTP) function
17/ Data transfer
18/ Camshaft adjustment solenoid
19/ Injectors or Self-adaptation of emission system at limit
20/ Vehicle speed signal
21/ Purge switchover valve
22/ Camshaft position sensor
23/ Intake manifold absolute pleasure (with engine running)
24/ Flexplate segments (crankshaft position sensor)
25/ Knock sensors
26/ Upshift delay switchover valve
27/ Not used
28/ Engine coolant temperature change monitor

mashbury

Thanks TC / Echo200 for replying.

I wonder if the codes you have are for the SRS system or for the petrol engine management. As far as I know my Diesel 300TD does not have any electronic management, only ELR (I think) electronic idle control of the diesel pump. There are also pins for this system on the 8-pin connector (I can see the wires going from there to the pump). No other pins are wired up so I guess I only have the 2 systems capable of diagnosis.

I've found out so far the meaning of the following SRS system codes...

3 = Ignition circuit or Driver's airbag
5 = seat belt buckle or pre-tensioner
8 = power supply

I'm not at all sure about this (although the code 5 was given by `JER' on your thread TC) and of course I think my fault code is 2 which I don't know.

I'd be very interested to learn how you get on with the dealer. I've read your saga on this forum, are they going to do it at no charge?


P

echo200

I'm not qualified to judge the list of codes I gave you and, from your comments, I can see how trying to be helpful can simply create more confusion.

The codes were originally supplied to me in response to my SRS problem, together with instructions on how to build a LED tool which, given my knowledge of electronics, probably looks more daunting that it actually is.

Thank you for drawing my attention to the existence of another set of codes. If you discover any more, please publish them.

Since my analogue check is at the request of Daimler-Chrysler UK, I expect them to foot the bill.

echo200

Clicking on the following link will enable you to download the CS1000 Fault Code Scanner manual.

http://www.autolib.diakom.ru:8000/CA.../cs1000_mb.pdf

It's a 910Kb PDF file and contains SRS code tables for 1988-1998 MB models.

Note that, since publication, I've edited the original (broken) link; hope it works now!

Jer

Code 2 is death. There is a fault in the control unit.

mashbury

TC/ Jer

Once again thanks for the replies. I'm glad I now know where the fault lies, although I suppose it's the worst news I could have. I'm determined to try to fix the fault (taking due safety precautions) without recourse to the main dealer, so I'll try to locate a new module at a sensible price, somewhere.....

Tried the link TC, but doesn't seem to work. Any ideas? It's tanalising 'cos it would seem to be just what I need for the full list of codes.

JER, you obviously know a lot, just to be certain before condemning the control unit, am I using the right procedure for measing the codes, and how do I (try to) clear them: I've read that you have to take pin 6 to chassis for around 6-8 seconds after you've read the code. Is it possible that the 2 fault is a stored historical problem?

By the way, the previous owner said the problem started during heavy rain (about 1 year ago!) and I have discovered wet footwells. The red SRS connector is down there so maybe the water caused a fatal short to the module?

Thanks again for your help guys. If I do discover the full code list I will publish to assist anyone else.

P

echo200

Sorry about the broken link. I’ve tried to repair it, but it sounds like it still won’t function properly.

I pulled this extract from the CS1000 Fault Code Scanner (Mercedes-Benz Instructions) PDF manual.

Analogue Codes (SRS)
Models: 124 and 129
Model Years: 1990-93


1/ No fault found
2/ SRS control unit self test failure
3/ Driver airbag squib
4/ Front passenger airbag squib
5/ Airbag/ETR, driver seal belt buckle switch
6/ Front passenger seat belt buckle switch (ETR)
7/ Front passenger airbag resistor
8/ Voltage supply interrupted
9/ SRS warning lamp (with flashing SRS warning lamp impulse counter scan tool button held too little time to read out the DTC memory or too long to erase DTC codes. Reread codes.
10/ SRS control unit activated.

Unless someone else can corroborate that these are definitely the correct codes for your model, I suggest that you show them to a M-B technician for confirmation.

Also, although this is probably irrelevant to your circumstances, there is a U.S. NHTSA Mercedes-Benz recall on 1992-95 models fitted with a front passenger airbag. This states that the front passenger metal footrest can, over time, abrade through wiring harness, causing short circuit; wires might then overheat, engine may stall, or airbag could inadvertently deploy.

Good luck!

mashbury

Managed to get the link going (computer firewall complained of some tcp ports) and get the pdf. Very useful doument indeed. It really does seem to have everything. Thanks a bundle for this pointer and all your help. I'm sure this will help others as well.

I must say it seems odd having the SRS connector sandwiched between two metal plates against the passenger's feet..bit of a bolt-on afterthought feel about it. I can understand the possibility of chafing wires. I have a hunch that in my case the connector got wet due to the windscreen drain conduits being blocked (I've since cleared them) and water running down the back of the bulkhead. When I lifted the carpet it was dripping wet in the foam pads..yet the carpet itself is resilient enough to let no damp show on the upper surface. Only hint was a funny smell, which I thought was the previous owner's aftershave!

Impressed with the forum..got a feeling I'll be back!

PS everyone, still interested to know the way to clear analogue codes.

mashbury

Managed to get the link going (computer firewall complained of some tcp ports) and get the pdf. Very useful doument indeed. It really does seem to have everything. Thanks a bundle for this pointer and all your help. I'm sure this will help others as well.

I must say it seems odd having the SRS connector sandwiched between two metal plates against the passenger's feet..bit of a bolt-on afterthought feel about it. I can understand the possibility of chafing wires. I have a hunch that in my case the connector got wet due to the windscreen drain conduits being blocked (I've since cleared them) and water running down the back of the bulkhead. When I lifted the carpet it was dripping wet in the foam pads..yet the carpet itself is resilient enough to let no damp show on the upper surface. Only hint was a funny smell, which I thought was the previous owner's aftershave!

Impressed with the forum..got a feeling I'll be back!

PS everyone, still interested to know the way to clear analogue codes.

Jer

Just as you said, you ground pin 6 for 6-8 seconds after displaying the code. I believe code 2 is erasable. Code 10 is the only one that is not.

mashbury

Yep, now got the procedure sussed. Thanks all.

mashbury

A cautionary tale follow-up to this thread. Having got a failure code of 2 means the SRS unit I have has failed its internal test, so I needed a new one.

Looked on E-bay and bought exactly the correct item from a guy in Germany for 116 Euros. Fitted it yesterday and guess what..a failure code of 10!!! This unit has been activated, i.e. presumably in a car that has had an accident. Not impressed.



In other words this replacement unit is completely useless &, unless this bloke gives me my money back then I suppose I just have to put it down to experience. Caveat emptor. as they say.

The old unit clearly had got very wet at some stage, possibly from the heater core leaking (?) which is directly above it. I opened it up, cleaned the cicuit boards and re-soldered some components, but having put it back again it still failed its self-test. Oh well, at least I'm back where I started, and I can change an SRS unit blindfolded now!

Does anyone know a reliable source of second-hand, or even `cheap' new SRS modules (and I suppose other Merc parts) in the UK?

Jer

Sorry to hear about the dud SRS unit. I hope you get your money back.

Potomac German Auto in the US is a good source for reliable, used components. www.pgauto.com.

Good luck!

mashbury

Arggh!

I've now bought another second-hand SRS ECU from I'm sure a very reputable Breaker, it arrived through the post within 24hrs of contacting them, excellent service.

BUT...

Fittted this unit and it also has a fault code of 10! The Breaker told me, before I bought it, that the unit had come off a car where the airbag had not deployed...yet a code of 10 means the SRS unit has been activated..or it thinks it has.

So I have a number of questions...

Does anyone know if it is possible for these SRS airbag units to be triggered by being roughly handled in the post, i.e. when they are not switched on? Does anyone have 1st hand experience of this?

Am I doing something wrong? I now have bought 2 ECUs through the post and both have the same failure code 10. More than a co-incidence, or am I just very unlucky? I'm pretty confident that I am fitting and checking them correctly, and the original unit still reports its failure code of 2 (self test failure) when I put it back in, so I don't think I'm breaking them during the installation process.

Is there any known way of re-setting the SRS unit once it has activated? I think not, I believe there's a mechanical once-only device inside, but maybe someone knows different?

I really want to sort this one without admitting defeat and getting a new unit from the dealer, and I'm getting rather despondent. Any suggestions gratefully received.

Jer

Some of these units were known to have an electrical fault which records a code 10, but does not output the airbag. I can send a page from the shop manual with more details, if you like.

mashbury

Hi Jer,

Thanks for your continued support. Yes please, I'd be very interested in the page from the shop manual.

Jer

mashbury

Jer, thanks, this certainly looks consitent with what I'm seeing. I must say I don't quite understand what the remedy is telling me, but I'll go chasing suspect grounds.

I'm getting a third replacement ECU sent now which the breaker assures me they have tested, and will very carefully wrap for the post, so I'll see how this one fares!

Thanks again for your help.

Jer

The "programmed repair" is telling you to visit a dealership and request a new control unit free of charge. This is not a recall, and as such, the dealership is not obliged to install a new unit. Play nice with them and maybe you will get what you want.