Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi Karen, it does sound like you are having several electrical problems that may all be linked.
In the first instance I would recommend a full vehicle diagnostic check on Mercedes STAR diagnostic tool to see what fault codes are being stored. It sounds to me like you may have an issue with a SAM control unit. These are multi function control units that take care of many functions including lighting.
There are 2 SAM units - a front and rear and both are interlinked
Faults with one of these can cause similar symptoms to what you have described
A common problem we are seeing at the moment is with water ingress into vehicles - often undetected until problems like this arise & then short out electrics as the moisture gets inside so I would have this inspected as soon as possible in case any other damage is caused. It may not be a water ingress isssue but we have seen many issues like this with the amount of heavy rain we are seeing
On the ML water can get in under the front carpets where the front SAM is located through the heater intake with bloched drains in the heater housing - or the rear SAM can get damaged by water entering through the rear lamps, tailgate or side window
Chech to see if the passenger or drivers carpets are damp and also in the rear tailgate where the spare wheel is located and behind the right rear storage compartment in the load area
If dry then it may just be a simple SAM failure without any cause - the diagnostic check should reveal if these are causing issues
Best regards, Paul
Hi Karen, do you need any further assistance?
hi! am here if you need anything else
Hi Paul, thanks for the reply.. I have just checked for dampness, but it is all dry. I Have taken it out today and opened it up to 70 and no problems whatsoever. For the last 3 months I have drove it on very short journeys, could that be the problem.
Hi Karen - well its good news about the no damp issue as this is something we have seen a lot of! It still sounds like a faulty SAM problem to me at this stage. I dont think that the short journeys would be causing an issue like this.
The first step should still be a check on Mercedes STAR to see what fault codes are stored
Hi paul, why does save mode come up. Also what sort of money does it cost to have the star diagnostic test done. My car has been perfect today, should i carry on driving it. Also last week it kept going into save mode, so I woyld turn it all off and restart it again, then it went completely dead, and I had to get a jump start, then it was fine again. I really appricate your help you have given me so far. Regards Karen
Hi Karen - the safe mode (I presume you mean limp mode - engine with lack of power) could be caused by issues from a bad SAM unit (voltage issues on supply from SAM) or may be unrelated. An initial diagnosis on STAR should not be too expensive, we charge half hours labour for initial diagnosis on STAR and would advise on any further costs if more involved diagnosis was required.
Hi Paul, thanks for your vaulable advise. Kindest regards Karen.
No problem at all Karen
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Hi Paul, ok I have had the star test done, and has shown up loads of errors on the car. Is it worth getting the front and back SAM boxes replaced. I had punctured wheel yesterday and you was right removed the spare wheel and it was floating in water. The back conpartment were the back SAM box is and the fuses are all dry the other side back light cluster is wet. Where is the front SAM box located ????? Here are some of the errors the star machine has logged. - emergency path of control unit A80 intelligent servo module for DIRECT SELECT is not present 9007, 9001 undervoltage supply, check component B70 crankshaft hall sensor, signal faulty, glow plug cylinder 6 & 1 open circuit. 900E local undervoltage at circuit 30 less than 9v. 9703 fault in CAN communications with control unit N10 front SAM control unit. Paul it goes on and on, should i replace the front and back SAM units, and if replaced would it resolve all of these problems.
Hi Karen - this is not too unusual as I mentioned. The front SAM is in the battery box under the drivers seat. I would have this inspected too for any signs of water ingress & would also be worth lifting the passenger side carpet as there are electrical connectors under here that can cause similar issues if damp.
It does very much sound like one or both of the SAM units may be causing issues but there may be other problems such as wiring issues as mentioned
With so many fault codes stored I would probably be clearing all codes to see what comes back - ulimately with control units like this the only sure fire way is to replace the module to see if the faults all clear & the vehicle functions normally - we usually have a couple of spare SAM units for most models just to fit as a test - thats how common a problem these are!
Obviously with water in the rear the vehicle also needs water testing to see where the leak is and this fixing as well - moisture can build up inside control units causing failure - also check all connector pins are clean & free from corrosion