I'm posting this for my sister's car. Her 2000 S500 has an intermittent start problem. Sometimes it will crank, but not start. It does not appear to be heat related as it will happen after a stop or after sitting for hours or overnight. She has owned this car since new and it has about 110,000 miles on it. I can't give you much more information than that as the car is 450 miles away from me.

It has been to the dealer several times, in fact it just spent 2 weeks there with the tech driving it everyday and taking it home at night. No failure to start for him.

It has set no codes in memory.

It has never failed while running, only during the start cycle.

As you can understand my sister is not happy with the reliability of her MB.

Does anyone have any ideas about what the problem could be? I'm thinking that it could possibly be an ignition switch??

 

Ignition switch or Crank Position Sensor both possible.

IF STAR DIAGNOSTICS was used and no codes set (if checked they should have a print out) then I would try a new relatively low cost (DIY) CPS sensor but my confidence is only about 25%. CPS leaves no codes but usually fails intermittently when hot.

Did the dealer use the same key as your friend or the spare? If the spare then try using the spare yourself.

Stuart

 

i had a similar problem and turned out to be the crank position sensor (about $50 sensor)
you can look at my post and see if your problem is the same:
https://mercedesforum.com/m_72057/mp..._/tm.htm#72057

 

I asked her and they have tried both keys and it happens with either one. It's looking like the CPS is going to be the least expensive "throw parts at it" item. Will try that and let you know.