Engine Check Light On

MB S500 2001 with 104,000 Miles.

This happened twice now, I came home shut down the car.roughly 5 minutes I need ed to go again. WHn I tried to start engine it will crank and not start. I tried it a few times then the “Check Engine” light on. I took another car out. Came back about 1 hour later, tried to start engine again and it worked. But the check engine was still on for a couple of days then it went out automaticaly. It runs fine afterwards. Can you give some ideas what’s going on? Thanks a lot. Andrew Wen, Southern California.

Get the code read. This car uses the ODB-II system, so, by law, any ODB-II code reader, even those at Autozone or Pep Boys, can retrieve the code. Post the code here. Even if the light is now off, the code is retained. It should point us in the correct direction to fix the problem.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP
  2. if the oil warning light comes on, shut off the engine ASAP
  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

Went to AutoZone, they no longer provide the “free read” due to complaints from Auto Repair shops in the area (taking away too many business). So I purchased a Code Read Unit. Unfortunately the code already gone - it’s only 2 days. So I’ll have to wait until it happens again. Until then, thanks for the help.

That’s strange…Even though the CEL goes off, the code that triggered it remains until the system is cleared…

You mean regardless the seriousness of the problem the code should remain?

Yes…Once a code is set, it stays until it’s cleared even though the light goes off. That’s how it’s SUPPOSED to work anyway…

The CEL ALWAYS comes on when you turn on the key. It will stay on until the engine starts. Your engine never started, so it stayed on. This is normal. No codes were set…

Actally, the Check Engine Light was on for a a day or so while I was driving and then it went off. Is it that every time when CEL on, it WILL log a code into the diagnostic module?

Actually with my understanding of the CEL sysetems, most of which the details are propriatary, only certain conditions will cause the code to stay stored in the computer, after the defect is corrected. For instannce, if you leave your gas cap loose, you will get a CEL for the emissions portion of the OBDII system. After you tighten your cap and complete a certain number of drive cycles, the code will clear and the light will extinguish by itself. There will be no evidence that you ever had a CEL. Other conditions, like an random misfire, might set a code and lock it in until it is properly cleared. If anyone has the exact details on what is required to set and lock the CEL, and what will extinguish the light by itself, I’d sure like to get my hands on it. I’ve been looking since OBDI came out and still cannot find any public information on that data.

Perhaps my problem is not serere enough when CEL went out and serveral cycles (start/stop) it cleared. Since I have the Reader now. Next time it happens I’ll run it right away to see if I can catch any code. I will post it again. Thank you. I learned quite a few things.

I managed to get the code (you have to turn engine on). It’s P0335.

I guess you’re replacing the crank position sensor. Google appears to report it being a favorite code across multiple models.

Codes can reset themselves after so many “good trips”. The definition varies from man. to man. The good trip being defined as a cold shut down (not just a restart) and xx number of conditions being met before the next cold shut down.

The code P0335 indicates a problem with the circuit to the CPS sensor, not that the sensor is bad. Look for a bad connection to the sensor.

Can you tell me (maybe a picture) where is the CPS located? Perhaps I can clean the connector or maybe even replace the sensor? Thanks.