I have searched the forums and cannot find an answer to my problem..

I have a 2003 C240 where the gauges sometimes do not work when car is started, along with turn signals, wipers etc. After researching I came to the conclusion the rear SAM was the problem so replaced the rear SAM and took the car to the dealer to program (gas gauge did not work after replacement). Dealer programmed and said everything is good. Nope, about every three or four starts the car starts and the gauges don't work. If I turn the car off and remove the key put the key back in and start again everything works okay.

Any idea what to do next as the problem is intermittent and the dealer says everything is working?

TIA,

Dan

 

Which gauges don't work? Different gauges get their data from different places.

I am not an expert - am new to these forums also. As I understand it, the instrument cluster just reads data on the CAN-C and CAN-B busses and runs gauges according to what it's seeing. Wipers work by the stalk sending CAN data to the front SAM which in turn actuates the mechanism. Turn signals similar, except both front SAM and rear SAM read data from the stalk and run their respective lights.

If you're seeing wipers, signals, etc not working that would seem to indicate front SAM, as those and much more (all exterior lights, mirror controls), go through it.

Speedometer and tach get data from the ESP control module. Fuel gauge from rear SAM. Engine coolant from front SAM. Not sure about all the other indicators. Thus the question about which specific gauges are not working. If the entire cluster is not working then maybe the cluster itself is getting flaky.

Not sure what led the conclusion of rear SAM unless fuel gauge and rear turn signals only weren't working? From symptoms described, sounds to me like a flaky front SAM, or the ignition module, which is the main (sole) communication bridge between CAN-C and CAN-B.

 

All gauges

 

Do lights in cluster fail as well? I would remove cluster and clean connectors with spray (like Dioxit). You can make cluster removal tool from a coat hanger.

 

If turn signals and wipers are also not working when the cluster isn't working, then it seems to me like an entire CAN bus fail. That makes me think of the CAN-B / CAN-C Gateway, which is in the Electronic Ignition Switch (EIS) Control Module. The observation that removing and re-inserting the key temporarily fixing the problem also seems to point to the EIS.

Pulling the cluster and cleaning the connectors is an easy thing to try first!

 

I know this post is a year old but I have to ask since I have the exact same problem. I have been searching the entire forums but I have not been able to find a solution.
Was this issue resolved?

 

If this problem happens after a flat battery or battery replacement it can be the front and rear sams are both blown if the key was in the ignition.

However, the problem looks like
- ignition switch issue (hard to diagnose) but causes information to drop out between CAN B and CAN C since it is the gateway.

- water damage

- damage to wires

Cars which have been repaired badly after severe damage or damp have all of these problems.