I took my 1994 C220 (107K) out for a long highway ride to my parents house...really the first time since I had the motor mounts/shocks changed last week. Car ran wonderfully.

Start the car in the evening to go back home and the "check engine" light was on continously as soon as I started the car. Shut off and restarted the car...light still came on immediately. Having no other alternative I drove home and the light was on all the time...but the car ran great...so I'm a bit puzzled.

A couple of questions:
(1) If the computer finds a fault, does the light stay on until the computer memory is reset? or by the light staying on means that the fault in happening all the time? (if it goes off, the fault was intermittent)

(2) What commonly causes this condition (oxygen sensor?)...any common problem with the C220?
Would it be OK to drive around for a few days?

(3) I have a friend that is a certified BMW mechanic and he has the tools to read OBDII fault codes...would the BMW tools be applicable? I understand the C220 is OBDII compliant (though not fully)...where is the connector?


Thanks,
Chandra
cbajpai@yahoo.com

Don't know if this is common to all "C" class but here goes. Had the same issue. Best I can tell the fault code is in memory until cleared/reset by the tech. CE light has several items that can trigger it. Do a search on CE and you'll see. My C280 has two O2 sensors. The first one (the expensive one 164.00 for me in Houston)senses the exhaust and gives feed back to the computer, the second one is a comparator, it compare what it senses down stream with what the first one senses and the computer makes the corrections accordingly. My MB tech was very encouraging to get it taken cared of soon, which I did and the engine light did clear. A hard lesson learned about this 'C' class also is do not refuel with the engine running. Reason am told by Houston MB dealer and my MB tech is that the computer senses a delta P in fuel pressure. It is sensing the expected fuel pressure and when the fuel cap is removed the then internal fuel pressure is changed thus giving a delta P and the computer registers it as a fault. So now with that lesson learned I will always cut the engine off when refueling. Hope this helps out a bit.
regards, LH

If I remove the battery...will that clear the fault code?
or do I need to go to the dealer?

-Chandra

Think I'll defer that to the ASE expert guys. My guess with today's technology you have capacitive circuits that will maintain a charge and thus retain the fault code in memory until reset. But thar is only a guess. Sorry, just a rookie, bet on Benzmac has the real soop on this. LH

I had the exact same situation after I refueled at a remote mountain gas station. The engine was off. Light came on, but car ran normally (so it seemed). If ignition was shut off, the light would come back on when started (code was obviously retained in memory). Got home, pulled diagnostic system fuse, checked and replaced. No more light, never came on again, car runs fine. The fuel/emissions systems are quite sensitive, apparently to changes in fuel system pressure, fuel, etc. This is based on my experience alone...

If you can, have the code read. See if there is any code that would allow damage to emission system. Then pull the diagnostic fuse(31 or 32) foe ten seconds with key off, to turn light off.

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