daffyduck

Hi all,

Need some advice. Please bear me with me as the story is a little lengthy.

Few months ago, my C-class W204 (Facelifted) petrol 4matic 72k KM mileage experienced the following symptoms:

1. Random violent chokes/shudder while driving
2. Random dead engine while driving with check engine light illuminated. Engine operation can be restored by restarting car. After restarting, engine would run fine without check engine light or any other alarms whatsoever. It would behave healthy.

The said symptoms were random. The car can be driven completely fine for a few days, then said symptoms will come the following day. Took car to local indie mechanic, who told me my car battery was weak, causing these symptoms and possibly damaged the engine control unit (ECU). He said that the battery brand that I was using on the car is bad and Mercedes car needed to use a certain brand (I won't name them here). I doubted his theory as I cannot see how a weak car battery can damage the ECU. Please correct me if I am wrong. Nevertheless, car battery was replaced with new as this was done when I am away from town (my dad handled it). After battery replacement, car ran fine for a week or so but started experiencing said symptoms again. One morning, car just wouldn't start in my porch. It failed to start throughout the day but successfully started up at night on one random try. I then took it for a ride and car ran just fine without any alarm indications. Car ran fine for a few days and then would not start again in car porch. Tried to start it for a few days but no luck. Called indie mechanic, he plugged OBDII scanner and could not pull any fault codes. He said its probably a dead ECU and disconnected battery from car. I decided to call Mercedes dealership to do a proper diagnostic and they sent a technician who also "diagnosed" the car to have a dead ECU (I wasn't there as I was out of town for work again, so I could not see how he check the car. My dad handled it). Mercedes dealership quoted us approx. $2K for ECU replacement. Indie mechanic told us the job can be done by simply replacing ECU with a second-hand. Second-hand ECU (which belongs to another W204), along with its electronic steering lock (ESL), electronic ignition switch (EIS) and key fobs would cost approx. $700. Dad went with the second-hand ECU since it's much cheaper and indie mechanic told us its a plug and play thing.

So then, after replacement of ECU, ESL ans EIS by indie mechanic, car could not start. He said ECU needed to be programmed. Suspected second-hand ECU had a different chassis number (VIN) programmed into it and therefore could not start in my car. Car started fine after programming was done by another indie mechanic. Just the programming itself costed me approx. $500. So now car can be started and run just fine, but its COMAND unit is giving "anti-theft protection activated" notice and I cannot use it. Seems like it has been locked out. It seems to me that changing the ECU has caused this, since the COMAND unit is likely linked to the VIN and will probably do a validation during start up. If the VIN of the ECU is not identical to the one registered in the COMAND unit, it will lock up. That's my guess. I've asked Mercedes dealership lead mechanic and he told me the same thing. I told him that I would like to take the car to dealership and see whether they can fix this COMAND locked-out problem for me. But he told me that if they connect my car to STARS, the current ECU (which is second-hand) might be locked out too since STARS will probably detect that the ECU does not originally belong to this car. I believe him as I don't think he has a reason to lie to me (I also happen to know him but we are not close). But he isn't sure and that I would have to take the risk myself. I am considering just letting dealership replace the ECU with brand new by paying the full price ($2000) and get this problem over with as this car has been on downtime for about 3 months. But now another issue arises. To replace the ECU with brand new by Mercedes dealership, they need to have the original ESL and EIS installed. As mentioned above, the ESL and EIS were also replaced with second-hand (one set with the ECU) by indie mechanic. The indie mechanic told me that the existing original ESL cannot be used anymore and I have also read that W204 does have ESL issue. Now I cannot make sure whether my car's original ESL is faulty (or was faulty, causing a no-start, but unlikely since ESL wouldn't cause car to randomly fail while driving on highway). Even if the ESL is not faulty, I would need to pay extra manhour for dealership to once again reinstall the original ESL and EIS into the car, and then proceed with the ECU replacement job. If, after the ESL has been re-installed and it was found to be faulty, they would need to replace it with new, and that alone will cause an additional $2000. Currently the car is still at the indie workshop and they are trying to do some sort of coding in attempts to unlock the COMAND unit. But I have read on forums that it is impossible to obtain the unlock PIN. Only replacing the COMAND unit with new by dealership would cost approx. $6.8K, as told me personally by dealership lead technician. So what are my options? Please give me some advice as I am currently stuck. I am considering installing aftermarket android player on the car, but would that work? Will the aftermarket android player affect the quality of the original speaker?

Please help! Perhaps someone came across this problem before. Do let me know if more info is needed. I will also update this thread.

Many thanks in advance!