GermanCarShow

2017 C43. A few times in the last month, when getting in the car, putting my foot on the brake, and pressing Start, the ignition will come on and the needles sweep the dials, but the engine doesn't start. This usually happens in the garage at home. Yesterday at a shopping center, I had to try 6 or 8 times to start the engine before it worked. No error lights or messages. No problems with (un)locking the car keyless. I searched the forums and the threads I found had no resolution. Dealers unable to duplicate problem, no codes in Xentry, etc. Any ideas as to the problem? Suggestions on duplicating the problem? I'll post this in the general w205, c205 forums as well. Thanks.

MaverickC43

Just throwing it out there and others know way more than me but if the car is not “seeing” the brake being engaged that could cause issue???

GermanCarShow

Over in the w205 sedan forum, a member said, "Same happned to me. Dealer replace the Spark Plug coil and the Camshaft sensor behind the engine. Work without errors now."
I believe for auto stop/start feature, the engine stops at a specific point where a cylinder is in the right position to fire and (help?) start the engine. If the same holds true for stopping the engine with the dash button, then position sensors might make sense. I have read posts about not being able to start the car on the street after auto stop/start had stopped it. I don't have that problem, yet! Just starting cold, and seldom at that. I'm going to start a log to track the problem and see if I can find any consistent conditions.

JMatters

I've had the same problems a few times on my 2017 C43. It hasn't happened in the summer, but it happened a number of times in the winter when it was incredibly cold out. I found taking off the start/stop button and inserting the key fob to start it the old fashioned way worked to correct it every time. I'd love to get it resolved but it happens so infrequently and randomly that it's not worth the time to take it to the dealer/shop.

GermanCarShow

@JMatters Thanks for adding to the info here. Good to know the key keeps me from getting stranded. It hasn't done it to me since 10 days ago at the shopping center. I am trying to track all starts to get a % of failures.

JMatters

No problem! Please let me know if you are able to get it resolved. It's a worrisome problem to have in the back of my mind.

White One

I have the same experience...It has happened to me about a half dozen times in 3 years, but the key works every time..no biggie

Tirgoman

Check the brake light switch, if the computer does not see the brake pedal as being depressed it will not let the starter motor operate. Try really pressing down on the brake pedal and/or having someone watch the brake lights. Replacing or readjusting the switch is easy. The eal issue is a slight loss of vacuum to the brake booster that results in having to press the pedal harder. I bet it happens when the car sits longer.

JMatters

That's a good idea. But oddly enough the only time I've ever experienced that problem was when it was incredibly cold (single digit temps) and after I stopped the car after starting it in the morning (i.e. stopping to get gas at the gas station about 2 miles from my house).