Intermittent starting problems
 

Hi all,

This is my first post here, apologies if this issue has been addressed elsewhere.

I have a 2012 E300 4matic. I am the original owner of this car and have been very happy with it except for the problem I am about to describe. The car is well-maintained and has about 80K miles on it.

About a year ago, I started the engine one cold evening and it would act in a weird fashion. A number of malfunction signals appeared in succession (cruise control inoperable, front left airbag malfunction, SRS malfunction, ABS inoperative, and a few others) and the gear would not get out of Park. I attempted to restart several times, to no avail. I got a ride home and got back to the car the next morning (it was parked outside my office building). The engine started, but with the same set of issues. As I was trying to arrange it to be towed to the dealership, I went back to the car after an hour or so to pick up some paper and decided to crank it up one more time, and (voila!) it started as if nothing had happened! No alarms, no problem getting into gear, just perfect as before. I drove the car to the dealer and explained the problem. They kept the car for a few days, but could not replicate the problem. They suspected the ECU but they were not sure. Since the battery was on the weak side (another shop had suggested replacing the battery a few months ago during scheduled service), we decided to replace it and hope for the best! For about a year, there were no re-occurrences and I was confident that the issue was resolved.

The same exact problem resurfaced last week after just about a year of trouble-free operation. Just like the previous time, it was a cold day and the car had been parked outside for about 9 hours. The same symptoms occurred and once again the car was stuck in Park. I noticed that the internal lights would not come on and none of the electronics would work this time (seat adjustment, radio, etc.). After several restart attempts and an hour break, the problem disappeared and I could drive home. A few days later, it occurred again, this time in the morning in a closed garage (again in cold weather).

I was wondering if anybody has seen a similar set of issues. Is replacing the ECU indicated? If not, what other parts could be the culprit?

Thanks in advance for any ideas.

Have you checked the current battery state of charge? It really sounds like a low power problem to me, especially since you went for a year with a new battery and no issues. Perhaps you have a minor parasitic drain that is taking down your battery. The new battery could also be bad. Not all batteries are equal and properly manufactured.

I would check the battery just to be safe as Key suggests. Also, I look into the F32 fuse issue. Read about it in this thread - the symptoms sound similar. https://mbworld.org/forums/e-class-w...d-respond.html

Check the resistance of the battery. Sometime voltage will be up to snuff but with resistance too high and battery will malfunction in the manner you describe. I believe that over 1.5 ohms is too high. I might have to verify that figure.

Change the auxiliary battery. $60 from the dealer, ~$20 from other sources. Easy DIY job.

Sounds like a CAN communication problem

Wanted to follow up on my thread with the resolution of the issue, in case other people find it useful.

I took the car to a MB dealer after the problem persisted for several days. (Every day was a 50-50 proposition, some days I could drive the car, other days I couldn't. I was lucky that it would drive on the day of my appointment, so I didn't have to tow.) They kept it for several days and found that the issue was with the pre-fuse box. Apparently, the internal electrical malfunction in the pre-fuse box was causing no voltage to be present between the pre-fuse and rear SAM. They installed a new pre-fuse box and cleared all fault codes and the problem has gone away.

I wanted to thank everybody in the forum who took the time to respond with helpful suggestions. Going to the service rep with relevant information was very helpful to me, I appreciate it.

Good to hear. I'd say Mr. Fish nailed that one!

OP, glad you got it fixed. Sounds like that is a hard problem to nail down. Mind sharing how much the repair was?

Not at all. It was indeed difficult for them to nail down the problem. Thanks to you, I was able to give the service adviser a concrete lead about the F32 fuse. They also seemed to have more knowledge on their own than they did in December 2016 (the first time I took the car to two dealers with the same issue).

They charged me $500 for labor and $250 for the part. The car was in the shop for about 5 days (they didn't have the part in stock).

Thanks again.

OP, thanks for the follow up. I always appreciate it when folks report back with the resolution.

Great call.