Originally Posted by
pizzaguy
This is an odd one. The RCM is highly suspect, but you have addressed that.
So it runs fine, but a lot of instruments/indicators are hysterical. You have a "Serial Buss" error code, that apparently means the ECU can't talk to SOMETHING it wants to talk to. That could be any module on the CAN bus that the ECU is on. Those modules are: Transmission Control Module, Shift Lever Module, SKREEM, Brake Controller, and Instrument Cluster.
LOGICALLY, Id probably suspect the Instrument Cluster because you say the car drives fine. The car can't drive fine if the ECU/SKREEM/Transmission Control/Shift Lever modules have a problem. But the Instrument Cluster in a failed state would not cause the ECU to not be able to run the car.
I do know there have been a FEW IC failures over the years. I'd be sure the battery cables, block to chassis jumper and alternator are good before I tore into that Instrument Cluster. I'd also do James' mod right away:
https://www.crossfireforum.org/forum...le-engine.html
Has this car had flood/water damage in its past?
Fixing or replacing the ground wire is a good idea. However, there is a reason that MB did not ground directly to the battery. The electronics are sensitive and need body grounding is likely the reason. My reasoning as a solar contractor and knowing the importance of grounding, is that they did not want a possible direct short going straight to the battery. It should go to the body and the inner fenderwell is a welded on piece of the body. Consider this, When a short occurs, the ground wire or grounding circuit, becomes a current carrying conductor. The grounding circuit will carry current until a fuse blows or a wire melts or a piece of electronics burns out. If a fault occurs and you are grounded to the battery it will send current to every grounding circuit in the car, as opposed to just the affected circuit that has faulted. You are essentially bypassing the fuse which is the primary protection of a circuit. Personally, I would not want any current going to the negative side of any battery. It could cause the battery to explode. ( I have seen this happen on grounds to batteries when a fault occurs ). It would be the same effect as trying to jumpstart with the cables reversed on the battery terminals. Reversed cables will fry the skreem and at the very least scramble the ECU at the same time, and in a millisecond. In German engineering, everthing has been well thought out, there is a reason for everything that they do. These are my thoughts based on my 22 years of experience with DC circuits and ground fault repairs. Solar is exactly the same as automotive as far as the DC side goes. The same rules apply to both. Grounds must bond to earth. Not a battery.