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The Benz stealership says my 2005 c230 with only 50,000 miles isn't worth fixing due to oil in the ECU, wiring harness, and O2 sensors (which is due to the problem with camshaft solenoids leaking). They showed me a tiny bit of liquid in the back ECU connector, though the front solenoid connectors definitely were oily. They won't install the isolation cables because they say the ECU, harness, and 02 sensors are already ruined.
So before installing the isolator cables, new 02 sensors, solenoids, etc, I'm trying to remove the ECU to check if there really is any problem with oil inside the ECU, but can't get it out. The problem is that there is almost no room between the T25 screws (with female torx heads) that hold down the ECU and the side of the engine compartment. I can't get even a socket driver in there, nevermind the T25 bit. Photos attached. Has anybody managed to remove the ECU and open it? If so, how?!
Background: this is engine #2 for this chassis. First one died at about 75,000 miles due to timing chain / tensioner issues resulting in valve contact. Replacement engine was used and I've only been driving it lightly for that last 7 months before I noticed rough idle and nearly stalling when coming to a stop or slightly after stopping.
Last edited by stenodinson; 11-19-2016 at 11:48 PM.
Reason: Added background info
Thanks RedGray. That was very helpful. Nevertheless, it looked a bit tricky to pull off the airbox and connections (or more precisely to get it back together!).
So I managed to find a mini-ratchet-wrench and got the ECM off in about 15 minutes.
Thanks also for the warning about swapping ECMs. I heard about that, but I hope I don't need a new one. My goal is simply to see if there is oil in the ECM (like Mercedes Service Dept claims). Looks like it will be hard to open though. Will search other posts to see if there's a way.
T25 bit on mini ratchet-wrench needed to remove four screws holding ECM to airbox. Ribbon attached was to recover wrench if it fell down to the skid plate.
T25 bit on mini ratchet-wrench needed to remove four screws holding ECM to airbox. Ribbon attached was to recover wrench if it fell down to the skid plate.
I'm glad that you got the PCM out. I like that tool idea. :-)
I agree with the Dealer that it's "safest" to replace the PCM. However, unless the electronics were bathed in oil, I doubt there was any harm.
My guess is that the most likely problem area would be from oil seepage into where the connector mates/solders to the PCB-board.
Although, it seems like FR4 (the PCB-board material) has has a good rating against oil. http://www.g10fr4.com/g10_pdf/CHEMIC...FR4,%20CNL.pdf
Also, the connectors are through-hole. So, the solder connection is on the back of the board to the pins, and also penetrates through the holes in the board.
It's just hard to say what the status of the oil is in the ECM without opening it. From what I saw in the post by SunnyRayToronto and his pictures (included here for convenience), it looks like there is no conformal coating on the ECM's circuit board.
Based on the lid damage on the left, it looks like it was very tough to open the ECU and this module can't be re-installed.
The crystal's leads lifted off the PCB solder pads likely due to Mercedes mounting the ECU on the vibrating engine rather than on the chassis. (Destructive testing of electronics is actually conducted using vibration machines! Why would they do this to the ECU in production!?)
Any oil would probably end up at the bottom. But as the car starts, stops, and turns, the oil could slosh around and cause intermittent connectivity issues. (I know oil is supposed to be an insulator, but with contaminants it can conduct a bit and I could see how it might interfere with high speed sensitive electronics.)
Last edited by stenodinson; 11-22-2016 at 01:22 AM.
Based on the lid damage on the left, it looks like it was very tough to open the ECU and this module can't be re-installed.
The crystal's leads lifted off the PCB solder pads likely due to Mercedes mounting the ECU on the vibrating engine rather than on the chassis. (Destructive testing of electronics is actually conducted using vibration machines! Why would they do this to the ECU in production!?)
Wow, just wow. Consider that, imho, the rear SAM on the W203 is a mega POS that even get a 2nd year engineer fired, I guess that I shouldn't be surprised.
Since the 50's, it's well known how to protect electronics from battery removal/install spikes. It takes very few cheap parts. Yet clearly, even the stuff that I taught in 2nd year Electronics Engineering is past their knowledge. Note, I'm not talking about a poor design for cost reduction reasons, I'm talking basic engineering.
The same is true for that crystal. It should've been either glued down or strapped down.
And, no conformal coating when the ECU is mounted to a hot engine above a hot supercharger. WTF????
Clearly, they all live in Las Vegas Nevada. Therefore, the common every day occurrence of condensation (going from hot to cold) never even entered their mind.
I agree that the above design shouldn't/wouldn't have survived a proper shake and vibe test per automotive standards.
Also, fwiw, those big quad flat pack ICs with fine pitch leads, should also have some glue/adhesive under the center of them.
Mounting the ECU vertically on the MB engine saves wire lengths. That means a lower cost.
But, that also means a higher/worse gravity/force/vibration effect on the IC chips.
Gee, even GM, that went bankrupt because they produced junk and had to be bailed out the the Government, mounts the ECU/PCM horizontally and they also put it under the air filter (cooler location, and less temperature variation).
Thank you for confirming my disbelief Red Gray! I'm an EE too. From what I'm discovering about the well known problem with oil contamination in the ECU and its bizarre root cause of oil wicking its way from leaking camshaft solenoids, I'm shocked that Mercedes has any brand strength. Basic engineering design practices seem to have been omitted and Mercedes won't do anything for me. I thought having to replace my first engine was just bad luck, but now I wonder how the M271 ever made it into production. So many processes seem to have been ignored -- from best design practices, to testing, to dealer maintenance, to customer care. None of my less costly cars ever had stupid problems like I've encountered with Mercedes.
on opening a Bosch ECU. The Mercedes ECU doesn't seem to have any screws/leverage points though so I'm also asking SunnyRayToronto if he has suggestions on how to open it.
11-19-2016, 11:32 PM
