W211 CAN Bus problems

[jay_bob]

Edit to add: central gateway (search optimization)

I have had my W211 for about a year and a half and it has been great so far. Until it started dying on my son for no apparent reason earlier this summer.

Back in June my son was driving the car from Clemson to Charleston, on his way to his girlfriends, late in the evening of course, and he calls me in a panic. Multiple warning lights and messages (ABS light and loss of ABS/ESP message was one I remember), dome light flashing on and off, a/c blowing hot and cold, etc. He gets the 'red battery' symbol so I am thinking alternator. He pulls off the highway and I get him towed back to Columbia.

Pull diagnostics with my Xentry and nearly every module in the car has multiple stored faults for CAN failure to talk to other modules in the car. Both power train and body buses have problems. And messages about CAN bus shorted and CAN bus shutdown. 8 pages of printout. Of course everything is a lower case f which means fault came and went and is not present now, (capital F means fault is active right now).

So I dig into the CAN bus distributors and can't find any corrosion or loose connectors. But I did find under the right dash that the CAN bundle was laying against the aluminum foot plate that protects the electronics boxes in the footwell. There was a slight chafe on one of the CAN wires. So I de-pinned that connector, heat shrunk the chafed wire, and put back together. And zip tied the distributor and bundle in a better location below the dash where it won't hit that aluminum plate anymore.

Before I purchased the car (private sale in spring of 2018) the previous owner had an indy shop replace the oil cooler seals. Well they did not replace the o-rings and gaskets on the intake tubing in the front of the engine. This caused soot to blow all over everything up front and the alternator was caked in black crud. I thought well I better go ahead and replace this thing anyway, and put all new gaskets in the intake tract, and clean this mess up, before giving the car back to my son.

So after getting the car back together it drove fine for about a month until my son decided to go visit his girlfriend again. This time he got there ok and was getting ready to head back home, and only this time it refused to crank. No spin at all. Another tow back to the house.

Pulled codes again, same sort of errors, not an identical list but many similar as the first time. And of course the car started fine once it got back to the house. Tow truck driver confirmed he could not start it at the far end, and in fact could not get it out of P, and had to use the emergency release to get it up on the flatbed.

Spoke to my friendly service advisor at the dealer who used to be a tech and he's real good about letting me bounce ideas off him. He said check for water intrusion and the worst 2 places on a W211 are the rear SAM in the trunk and the ZGW under the dash. He said the trunk water comes from bad trunk gasket (duh) and the ZGW caused by plugged sunroof drains leaking water down the a-pillar into the wiring behind the dash. The ZGW faces up under the knee cover and the wiring harness wicks water drips down into the connectors.

First went to the trunk and pulled the left liner to see if the rear SAM was getting wet from a trunk leak. Everything was completely bone dry with zero evidence of any kind of wet back there. Pulled the plug with the body CAN wires and everything looked pristine.

Next I dropped the knee cover on the drivers side to reveal the ZGW. It is a little gray box about the size of a deck of cards. When I pulled the plugs out I saw evidence of corrosion. I popped the module off the knee cover and opened it up. Sure enough there was corrosion inside on the plug pins going into the circuit board, mostly on pins 7 and 8 and 9 and 10. Pins 7 and 8 are the engine CAN and 9 and 10 are the body CAN. Lots of green grunge growing between the pins.

I got some isopropyl alcohol (91%), wooden toothpicks, and cotton swabs and was able to clean up all the corrosion. Flushed everything out really well with alcohol and then let it dry overnight. I put the module back together and put it back in and the car started right up.

Took the car out and ran several errands so went through about 6 or 7 start/stop cycles and everything running good.

Tomorrow I will pull the dash area apart and verify the source of the water leak.

Just wanted to pass this along, if you have a W211 that is having CAN bus issues check the ZGW module.