echo200

This posting is a consolidation of earlier references to diagnostic issues arising from an SRS warning light.

My 1995 E200-124 has just been tested by a Mercedes-Benz dealer and these are the results.

1. Star Diagnosis test: no readings.
2. Analogue diagnostic test: no readings.
3. Handheld scanner: complete readings, except for SRS control unit.

Therefore, the dealer is maintaining that the fault must lie with the control unit. This will cost roughly UKP 750.00 (USD 1400.00) to rectify.

The independent specialist I have been using couldn't trace the source of the fault, using test methods 1 and 3. During their investigations, they swapped my control unit with their garage 'loaner' (an older E300) and claimed that my control unit worked perfectly well in the other vehicle, i.e. the SRS light didn't appear.

So, on the one hand, the dealer claims that I need a replacement control unit whilst the independent specialist says otherwise. Can anyone explain this diversity of opinion?

Also, I should appreciate a layman's description of how a handheld scanner works, particularly why this device should be the only method to reveal the fault.

Jer

This sounds bizarre and shady. If the control unit worked in another vehicle, the problem in your car must lie in a certain "point." It could be the belt buckles, airbag modules, or something else. Typically the shop can hook up the "contact box" to take electrical readings on the equipment and wiring.

A handheld scanner is typically for reading ODB-II codes. However, an MB of such age as yours most likely uses the pulse readout system I described in a previous post.

echo200

The analogue diagnostic I mentioned is the pulse or blink test and, according to the dealer, no readout was obtainable.

What are ODB-II codes?

Jer

Your car probably does not have OBD-II codes; it's too old.

mashbury

Hi,

It sounds as if it would be worthwhile doing your own analogue test, to prove that the `experts' are getting it right.

In your previous thread you wrote:

"With my U.K. version, for example, there's a 16-pin diagnostic box on the left side (assume you're standing in front of the car) of the engine-bay, located behind the firewall and to the front of the brake fluid reservoir. The sockets are very clearly marked in white 1 to 16."

From my limited experience and reading around, this would imply to me that you have the analogue pulse code system.

Your vehicle is later than mine, which has the 8-pin diagnostic connector. On this is was very clear which the SRS pin was, since the wire came from the fusebox, and one of the fuses was described as `SRS light connector' or some such ( it performs other functions as well).

This wire is connected (by the SRS ECU I presume) to chassis (0 volts) in sympathy with the SRS light on the dashboard.

To view the pulses you just need an LED and a 470 Ohm resistor. Connect one end of the resistor to a permanent 12V line from the car, connect the other end to the anode of the LED. Connect the other leg of the LED to chassis and it should light. If not, reverse the connections to the LED. You then have a functioning test tool.

Now connect the `chassis' leg of the LED to the relevant diagnostic connector pin: on the 8 Pin diagnostic connector the SRS is on pin 6. When this line is at chassis potential (0 Volts), as it will be if the SRS light is on, then the LED will light.

To view the code, short the SRS pin to Chassis for around 2 -3 seconds. The LED will remain lit, but then will flash...count the pulses, this is your failure code.

Do the same procedure again, and if there is more than 1 stored code you will now see the new code. Repeat this until you have cycled around the stored codes. Use the list from the previous thread to see what the codes mean.

To clear the codes, having just observed a code, immediately connect the SRS pin to chassis for 6 -8 seconds. Repeat for all codes. Any that will not clear, must represent faults that are still present.

In my case, I have fault code 2 which indicates that the SRS unit has failed its internal self-check.

Hope this lengthy explanation is of use to you. If you find you also have a faulty control unit, and bearing in mind that your Independent garage reckons your unit is OK in another car, perhaps we can swap!!

echo200

Thanks for all your advice.

The problem now is that, with no feedback from the analogue test performed by the dealer, I can’t see how performing the tests you suggest is going to make much difference.

Besides, I know the Service Manager at the dealership I used (up to last year they had serviced my car for the previous 3 years) and he’s a real ‘hands-on’ Manager, not some kid who just plugs in a computer and hopes for the best!

I seem to have won the battle and lost the war. There is certainly something very bizarre about a procedure that requires THREE separate diagnostic processes and then can only suggest a possible fault.

In view of all the time, trouble and expense already entailed, I am currently negotiating the cost of repair with Daimler-Chrysler UK.

There is also another way of looking at the outcome. I now at least have a fixed price for rectifying this fault. If replacing the control unit doesn’t solve the problem, the dealer has guaranteed to resolve the issue for the agreed price. So, if they discover that the only solution is to manually check the wiring, I will have avoided the ‘blank cheque’ scenario I was originally facing.

Finally, the independent specialist garage ‘loaner’ used to swap SRS control units was an older Series model. It has been suggested to me that only a ‘like-for-like’ swap would have given an accurate return. Any truth in this comment?

jem

I have a 1990 300-TE. I had exactly the same problem with the SRS warning light. I didn't change the control unit like the main dealership told me I had to. I found that under the passenger seat (in the UK) there is a little two-core wire connector: a simple push-connector which leads from the floor to the base of the seat. My wife had pushed a large road atlas under the seat after a recent journey and the book had pushed the connector apart. I pushed it back together and hey presto! no SRS warning light.

I paid the main dealer and two independent M-B specialist garages to check out the system for a fault and none of them located this mind-numbingly simple weakness.

Just check it now...

(If it *is* the root of your problem, please email me back to let me know.)

Best wishes

Jem

echo200

Having taken your advice and checked under both front seats, I can confirm that the push-connectors are firmly mated together and properly clipped to the floor.

I checked for loose wires and I even tried this with the SRS light illuminated to see if it responded to any movement in the wiring. There was no reaction.

Thanks for the suggestion though but, sadly, it looks like I'm running out of inexpensive options

mashbury

Note that if you disconnect the plug under the seat (which connects to the seatbelt `klunk-klick' socket) and you have had the ignition on, you will have introduced another code into the SRS ECU. Once the plug is put pack, you can clear the code again. Of course it will still be on if you have another fault.

On your point about waggling the wires, I think ( not 100% sure)that if the problem is an intermittent wiring fault, as soon as the SRS ECU has detected the problem once and stored it , the light will remain on even if the intermittency subsequently goes away. In this case then you would need to clear the code.

Don't forget to let us know what the fault turns out to be when finally discovered! I'm intrigued.

Good Luck.

echo200

The car is now booked in at Mercedes-Benz of Harrogate on 18th March, ostensibly for the SRS control unit to be replaced.

To add insult to injury, I have been forced to pay in advance for the control unit itself, because the dealer maintains that this is not a normal stock item and they cannot order the part on a 'sale or return' basis from Daimler/Chrysler. In all my years of using car dealerships, I have never been asked to prepay for anything like this before.

Speaking of Daimler/Chrysler, in their latest letter they offer no apology, no repair cost offset for the time and expense already involved in this episode, just a litany of excuses.

The worst aspect is that I was genuinely leaning towards buying a new vehicle when my current car comes up for replacement. Regrettably, there's not much chance of it being a Mercedes now.

On a more positive note, I haven't allowed the cost of the SRS repair to influence an earlier decision I made to extend the life of the car by investing in two new front wings. I even obtained a discount for having both wings replaced simultaneously AND I didn't have to pay in advance (obviously then not from a Mercedes-Benz dealer!).

I just want to take this opportunity to thank everyone who has tried to help with this issue. If Daimler/Chrysler Customer Service operated like this forum, maybe we could all find the answers we are looking for.

I'll post the results of the repair.

echo200

I took my car in for repair at 0800 on Thursday, 18th March. Later that day, I received a telephone call from the dealer stating that the SRS control unit they had pre-ordered was not the correct part (wrong terminals).

Although the reordered part arrived on Friday, at the time of writing (1800 on Saturday), the work remains unfinished because the mechanics are struggling to reset the codes.

This raises two questions.

1. Does the fact that the dealer is struggling to reset the codes necessarily imply that this is a wiring problem and that, therefore, the original SRS control unit was not faulty?

2. If they have fitted a new control unit, can I legally demand the return of the original control unit or does 'ownership' of the unit pass to the dealer?

Getting a fixed-price repair quote, with a dealer-supplied A140 courtesy car thrown in, is now beginning to look like a good deal!

More later.

Jer

It is possible if the techs could not interrogate the fault codes from both the old and new control units, that the wiring from the diagnostic terminal block to the control unit plug under the passenger foot well is damaged.

There are no core deposits on these control units (as far as I know), so you should be able to retrieve the old one.

Another thing: when the new control unit is installed, it is free of fault codes. If the techs are trying to clear codes on the new unit, there must be a problem with one of the SRS components (belt buckle, air bag module, etc.) which is causing the control unit to report a fault. They should check every point in the system!!

Thanks for keeping us posted. I wish you well.

echo200

I have just received my car back from the dealer after two weeks.

According to a copy of the worksheet, the main points include removing/rebuilding the centre console and panelling, removing the airbag, resistance and continuity checks on all wiring loom ends, cleaning of all end connectors and replacing and recoding the SRS control unit.

Since the vehicle was also due for an M.O.T. test (under U.K. law, a 12 month mandatory requirement on vehicles over 3 years old), I elected to have this work performed before I collected the vehicle and a couple of minor problems (bulb and a steering damper leak) artifically inflated the total cost.

The bulk of the cost was due to the new control unit @ UKP 553.00 + 17.5% tax (circa USD 1180.00). In total, I finished up with a total bill for UKP 850.22 (circa USD 1550.00).

Was the new control unit necessary? Well, I have to balance this question against the alternative, which is what I have described before as the 'blank cheque' route. Had I sent in the car for a complete wiring overhaul, it is likely that the labour charges alone would have been crippling. The dealer claimed that they spent 18 hours working on the car; at UKP 77.00 per hour, that would have come to UKP 1386.00 (circa USD 2500.00) plus parts (it may still have required a new control unit).

You could say that, in the end, both sides gambled. To get my fixed-price estimate, I chose to replace a part that may not have been the root cause of the problem, whilst the dealer clearly didn't expect that the repair would prove so time consuming.

No doubt some of you will be wondering why the 18 hours labour was spread over two weeks. From what I understand, the technicians were constantly being called away to deal with other matters, presumably warranty repairs. I guess that comes down to a question of old v new priorities.

What is less excusable was the dreadful feedback. I had to chase Service Reception for progress updates and I kept getting conflicting signals and callback promises that were rarely kept. This problem seems to be a feature in a recent survey of the U.K.'s worst dealers - see Issue 800 of 'Auto Express' (www.autoexpress.co.uk). Out of the 34 listed, Mercedes-Benz came 23rd.

Finally, the new SRS control unit carries a 12 month warranty.

echo200

Unfortunately, when I collected my car from the Mercedes-Benz dealer, it was early evening, pouring with rain and the light was failing. I, therefore, only noticed a number of problems on the following day.

1. The front offside wing had a substantial dent around the crease line, just behind the light cluster (fortunately, undamaged). The paint stress on the wing lip bordering the light cluster gave some indication of the impact. There being no sign of peripheral damage or paint residue, in my opinion this must have been caused by a heavy blow from a blunt object.

The dealer's representative was obviously reluctant to accept responsibility for the damage after the car had been removed from their premises and his questioning of the staff involved with the car drew a blank (well, there's a surprise!). His best offer was a goodwill discount on my next service, on top of the 10% discount they are now offering on older models. Since I already had two new front wings on order from a bodyshop, I accepted his offer.

2. The wood fascia, which had been removed/replaced during the wiring checks, was filthy and badly smeared.

3. The plastic trim around the automatic shift housing was incorrectly positioned, but I easily remedied this.

4. Also in the centre console, the electric window knob is now loose - how should it be secured?

I guess that, having resolved the SRS problem, the dealer couldn't wait to shunt my car into the customer parking lot which, incidentally, is the most ridiculously small and (usually) congested space you can imagine.

I can honestly say that I have never had a car returned in such poor condition by a dealer.

mashbury

Thanks for keeping us posted on the results, fascinating story.

Are you any the wiser as to whether is was the SRS unit at fault or a wiring fault? Logically I suppose it must have been a wiring fault, since it would only take a few hours to replace and reset the SRS unit, and I'm sure they would have tried that first. Yet they don't appear to have actually replaced any wires or connectors. So perhaps it was only a dirty connection after all that?

One can imagine their frustration spending 18 hours trying to get to the bottom of this, hence the implication of the damaged wing.

For my part, I've purchased a second hand SRS unit off E-bay (from Germany), bit of a gamble but it cost `only' £60. When I get time I'll swap it out. I'm prepared to be disappointed, but who knows? I'll continue my story on `my' thread later.

Regarding the electric window switch, these come away with the centre console panel, and are a plug-fit into their respective sockets. Just pushing it down hard ought to re-seat it...does it still work?

Anyway, good luck. Let us know what happens in 12 months and 3 days time!

brett

i had a similar problem-it may seem simplisitc but if you pull up the passenger floor board and make sure the SRS loop is connected that may be the source of the problem.

echo200

Firstly, I must apologise for inserting a misleading description of a problem in my last posting.

I wrote ....... the electric window knob is now loose - how should it be secured? I was actually referring to the knob which controls the electric wing mirrors. The mechanism works fine, it's just the knob which needs re-seating. I'm not sure how how much pressure to apply in case I break the flimsy-looking plastic connection.

Briefly returning to the SRS issue, am I any the wiser after all this time? Even after obtaining a copy of the technician's worksheet, I still cannot pinpoint the location of the SRS fault. This, of course, was always the crux of the matter. I'm even willing to bet that the technician may have stumbled across the 'cure' without even realising it!

I just hope that when I buy my next car, computer diagnostics will be equal to the complexity of the car.

Finally, I just heard of someone being charged UKP 95.00 (USD 173.00) to replace an electrical switch (fault - rear lights flickering on and off). Not a Mercedes, but a Ford Ka 1.3!

echo200

I keep hoping that I have written the final chapter in this saga and then I discover something new.

Anyway, the straw that finally broke the camel's back was when I discovered that the backlighting on the transmission console and on the heater dial controls was not working. Small items like this, and the fact that someone clearly couldn't be bothered to properly secure the carpet in the front passenger footwell behind the panelling, has caused me to make a formal complaint to the MB dealership I have used for this repair.

Also, I still cannot reattach the door mirror knob in the centre console. Someone suggested the obvious idea of using 'super glue' but, that doesn't make sense because, if the knob needed removing again for maintenance, then it would have to be broken off.

The (new) Service Manager keeps harping on about the amount of unpaid time they devoted to the SRS repair, as if it is some kind of excuse for sloppy workmanship. I would be the first to agree that they took a gamble on costing the entire job on replacing the SRS control unit and lost. Equally, I had to stump up for a new part when I'm fairly sure that there was nothing wrong with the old control unit. Frankly, this is the craziest way to get a car repaired I have ever encountered and I think that the dealer has one hell of a cheek to now claim that they really
shouldn't have taken on the job for a fixed price.

The car is being returned to the dealer next Friday for all these totally unnecessary problems to be sorted out. Before then, the two new front wings will have been fitted by the bodyshop I use (not the MB dealership). I just pray that those parts of the car come back in the same condition!

Jer

Damn bloody dealership. I am very sorry to hear about all this hassle. I hope they make good on rectifying the carpet and mirror switch problems, with no cost to you. I had a similar experience with a body shop. They repainted my car for $2,500 and in the process cracked the outside temperature LCD (heat in the paint booth for curing), and screwed up the wiring for the left headlight wiper. The guy who manages the shop is decent and friendly, but later he said "I'm not gonna rebuild your whole f***ing car." As in your case, if the shop wants to give you a break on the price, it does not relieve them of doing quality work.

Don't let this get you down. Hang on to your Benz and take good care of her!