My 07 runs and drives like a dream, except when for no reason while driving at any speed, all the dashboard lights go on, beeping and guages JUMP to 70mph, Tach goes to 6,000 rpm and Temp jumps from normal to hot, and the radiator fan goes to "supersonic". I've replaced the RCM with a rebuilt "upgraded" one. I've installed a 4 guage ground cable from the - battery terminal to the Bell Housing on the Transmission. And years ago completely disconnected the alarm system/siren. DOES ANYONE KNOW HOW TO FIX THIS??? Please help!

Parked with key out of the ignition. What could the problem be?

 

I wonder if you have water in the passenger foot well under the carpet. The Transmission Control Module (TCU) is located there. You could have a bad Instrument Cluster.
Before taring into things get a good diagnostic scan it should get you headed in the right direction.
You posted this in the wrong section; Perhaps a moderator will move it to trouble shooting.
When did you install the RCM?

 

First step when using the "symptom-function troubleshooting technique" from electronics is this: Does the engine keep running fine while this is happening?
The answer to THAT tells us what direction to go here. Your post implies that the engine runs fine the entire time, but does not state that directly.

 

Hi Zip, the RCM was replaced last summer. I will look into water under passenger floorboard and TCM. Thanks!!

 

The engine runs fine, but the radiator fan goes into supersonic speed mode.

 

Let's look at this:

The engine runs fine.
This means the ECU/PTCM has all it needs to run the engine, so we know the ECU has inputs from the cam and crank sensors, it has valid signals from the MAFand TB, and is telling the TB what to do with the throttle as well as telling the injectors how long to fire and the plugs when to fire.

The Instrument cluster gets most of its information (like for Tach, engine temp) from the PTCM. The speedo is driven by the brake controller.

The fan controller runs the fan at the speed the ECU tells it to, if it loses contact with the ECU, it runs the fan in emergency mode - FULL SPEED.

So, what ever is happening is stopping the ECU from talking to the Fan module and, at the same time, the instrument cluster is also loosing valid data.

See, I'd just blame the IC, but the fan speeding up makes me think otherwise. THAT one clue is what has me stuck, we know that it's part of the symptoms, but it does not "add up" with the other indications.
I'd say CAN BUS C is having an issue, but that would not explain why the fan controller is going nuts. Or would it? Could that be enough for the ECU to spin the fan fast? See, the fan module and the ECU talk over a single wire data bus that is not connected to ANYTHING else.

You almost make me think the ECU is the problem. I'd call James and Josh at the Mercedes Swap Shop, they do ECU mods and such, they'd know the intricate workings of the ECU better than anyone - you have an electronics issue, no "Mechanic" can fix this, Josh can.

 

Thank you!!! Do you have a phone number for James/Josh at the Mercedes Swap Shop? I live in Michigan, and have no idea where the swap shop is located.

 

Look up Mercedes Swap Shop on the Internet.

 

Have you checked the DTC's - a P0600 code is probably a CAN BUS failure. It might be an intermittent connection - I had a CAN BUS wire open at a splice. My initial fix wasn't very robust, and when I was driving the car, all of a sudden, the IC would go crazy, and many of the warning lights would come on. After a couple of seconds it would go away, only to come back a few minutes later. I re-did the fix (soldered everything), and I haven't had that problem ever since.
Good Luck
-Jerry

 

This is a very good idea. CAN BUS errors (those the ECU sees) tend to set off codes.