Zevs

2008 C300 4Matic. Car came in for a misfire. Attempted to scan modules, unable to connect to any module. The scan tool does light up when plugged in. Customer also stated that they had it at the dealer, and they were unable to remedy the problem. All help would be appreciated. Thank you.

W204Motorsports

take the driver side carpet out and check the SAM box, I've seen this problem once and all the wires/modules were corroded. Very bad design putting so much electronics right under the driver's feet when water is guaranteed to get in. Weather tech mats are a must if you live in areas where you get snow and personally, I took it all apart and coated everything with dielectric grease, including some extra covers to prevent this issue altogether. Good luck.

Zevs

I removed both front seats, and both front carpet sections earlier today. I did not see any modules on the floor.

W204Motorsports

If you open those black covers and see a whole bunch of corrosion, it's not a good sign.

Zevs

I checked the wires earlier. No green crusties. I also removed the connections, didn't find any corrosion on them. There was a very small amount of water on the floor. The carpet and foam was not damp.

W204Motorsports

What exactly isn't connecting with the scan tool? And what kind of scan tool is it? Are you able to connect to any module or is it just the ECM? If you are not able to connect with anything, I would start by checking a wiring diagram for the OBD2 port and check if each wire is doing what it should.

Zevs

My scan tool is a Snap On. When I plug it in, it does light up, it has power at the pins. 4, and 16, if I remember. No modules read, it won't pull up the vin.

Adi-Benz

Check fuses on front box driver side under hood

Zevs

The number 16 5amp fuse is good. There is power at the dlc. Also tested all other fuses in front and rear sams. All fuses are good.

Just204

You have a bad module or short to ground imo. Unplug one module at a time and see if the scan tool reads. If no, reconnect that module and go to the next one. Start with the easy ones. If you disconnect a module and then have communication that module is bad and is the cause of no communication. If this approach don’t work you need to inspect the cars wiring.

Zevs

Yesterday, I unplugged the connections on the underside / back of the under hood fuse box, thinking I was unplugging the modules. Is this not correct? There is very little information in Alldata. If this is not correct, where are all of the modules? Obviously the ECM in on the engine.