Bought a 2012 ML350 Bluetec (60k miles) for the GF to drive. Great car, love the torque and economy but there is a big problem. Sometimes immediately and sometimes after 5-10 miles, the turn signals completely stop working. Dangerous to say the least. I thought it might be related to the blind spot assist, so I turned that off but the problem persists. I've looked for answers on the forums and although at least one other person had the same issue, there was no solution presented. Is this issue really that rare?

 

Yes there is a solution, its a simple circuit consisting of the stalk, the relay and the front SAM, your issue is that you want a free solution and that there isn't------find someone with DAS Xentry tester and you will learn the solution in five minutes----else--live with it!

 

Ummm, nice 'effort' Plutoe, but try again. My 'issue' is that I'd like to be more informed about the system, how it works, what it interfaces with and what the common (if there is one) failure point is in said system. In case you've forgotten, that's one of the primary things these forums are good for - knowledge. IMHO - there is no better way to minimize the chances of being screwed by a service department (dealer or independent) than to know exactly how something works, so when they make a suggestion, your only option isn't to just nod your head, say OK, open your wallet and hope they know what they are doing.

 

Guys seriously? Im sure he wasnt asking for a free option as to how to fix the issue, from reading the OPs he never said he wanted a free option. Keep it civil

 

It seems like the 'cancel' function (turn signals automatically turn off when turning the steering wheel in the opposite direction from the actuated signal) is also erratic. Sometimes it doesn't cancel unless you tap the stalk in the opposite direction. I've had that mechanism apart on several other vehicles I've owned and it's always been a simple mechanical device on the steering column. Has Mercedes 'modernized' this tried and true design and made the turn signal cancel function purely electronic?

 

Electro-mechanical switch integrated in to the stalk.

 

The only time my turn indicators acted strange it was in concert with a failure of blind spot assist and some strange behavior with my seat controls and interior lights. The dealership replaced two separate Signal Acquisition Modules that failed. No idea what caused the failure.

May not be be the same problem, but it seemed SAM modules can cause pretty strange electronic behavior despite everything else seeming normal. Since having them replaced, no other odd behavior. Not sure if there’s a handy way to repair a defective module, but the service advisor told me how many different electronic control components were in the ML and I was surprised.

 

I'm leaning towards it being a purely electronic issue as shutting off the ignition and restarting the vehicle causes it to work again every time, if only momentarily. It does seem to be getting worse as time goes on. I have an appointment for Monday at a trusted independent with the correct MBZ full-on chassis computer. He 'should' be able to diagnose it. I'll certainly post with the results.

 

In preparation for meeting with the mechanic, it would be great to know how many SAMs there are in the vehicle and their location/function. I saw a GREAT write up on another forum regarding SAMs in a S500 but can't find anything comparable for the W166. Are there separate left and right front SAMs or just one for the front? Might be worth putting eyes on the one responsible for the turn signals and checking that everything looks to be plugged in and 'normal' prior to taking it to the shop.

 

i have seen several combination switches replaced for that problem, including mine.

 

When you had this issue, would turning the ignition off and back on 'reset' the system and make the turn signals work again? I'm trying to understand how a simple electro-mechanical item can fail in that way, but I suppose since the output from that item feeds into a module (not directly to the bulbs) anything is possible.

 

not sure if turning the key off and back would help, but canceling them and turning them back on would sometimes get them back working, i think th problem is the contact switch in the stalk, but nothing is sold separate, only as a unit.

 

Answers to two questions. The signal cancelling feature is mechanical. You can turn your steering wheel with everything off and the signal will cancel.

Second, while the signal is a switch, the input of the switch is read by the Steering Control Module at the top of the column. Then that signal is communicated to the Front SAM via CAN. If after the signals quit working, but you can get your hazards to come on, I would suggest that your SCM be replaced. Hazards are requested by the Upper Control Panel over LIN, but also to the Front SAM. The front SAM is located on the right side of the dash directly under the A pillar.

 

This happened to my father's ML350 BT, same model year. We ended up having to have the whole steering column unit replaced. It cost us $1100 CAD through the dealer. If you would like, I can dig up the diagnostic sheet, and upload a pic for you.

 

Yes, that would be great - Thanks. Truck is at the mechanic's today and it would be great to be able to match up your diagnostic with his...

 

Here is the diagnostic printout. Note that this is after the tech cleared the existing codes and then drove the car around for a bit. During his drive, the turn signals and blind spot assist worked fine BTW. Seems strange that it takes a while for the errors to build up to the point of turn signal failure though. Any ideas?

 

Sorry, I've been away for a while. I'll upload a picture of the diagnostic sheet later today.

 

I had this problem on my 2014 ML 350, supposedly. I never saw it but it happened at the dealer when they were trying to diagnose an issue with the sunroof. that was at 28k miles a few months ago. Now My driver side rear turn signal isn't working at all! LED strip is out cold. At least the car is smart enough to use the brake light as the turn signal now, Anyone else have this problem? It has been raining where I'm at all day so maybe moisture got in there?

Have to say I am disappointed with this car. I'm only at 32,000 miles and have had so many issues. More than I've had with my 2001 E320 that has 140,000 on it.

 

Hey OP, I've attached a copy of the service sheet.

 

Thanks Tej7. Certainly looks very similar to my issue. I have a replacement assembly coming from an auto dismantler ($200, with warranty) and the install looks very straightforward. Likely have to have it coded at my mechanic's shop but we'll see (same year and model donor car so I might get lucky.) I'm definitely going to dig into the old switch itself and see if there is anything obviously wrong mechanically or with the electrical contacts/connections. If I find something fixable, I'll post the solution here.

 

Be careful with your clockspring, you can't guarantee that the salvage yard ensured that the wheels were straight ahead when they pulled the assembly. Its a little more than two turns to each side so turn it to the left until the clockspring starts to get tight and then come back two turns and make sure its straight ahead.

 

Thanks for the info - I'll make sure to check that!

 

New (used) part is in and the both turn signals and blind spot warning are functioning normally again. FYI - I did have to Youtube the airbag removal as Mercedes has done away with the two torx screws and gone to a simple push-to-release arrangement hidden underneath a couple of innocuous looking indentations in the back of the steering wheel. It was a 15 minute job and no recoding was needed with the new module. Next is to take apart the old turn signal switch and see if anything is obviously wrong with the mechanicals or visible contacts. I'll update with what I find (if anything.)

 

 

Another one-post wonder. Did you bother to read the whole thread?