Keyword: W210 CANBUS diagnostics and repair, CAN B diagnostics and repair

Thought I would post a few items as reference for others who may have CANBUS issues. Be advised the W210 CANBUS is much less complex and uses different voltages than the later versions.
Issue: Front door control modules (DCM) and lower control panel (LCP) would fail. Front windows inoperative, side mirrors inoperative, seat adjustments inoperative, steering wheel adjustment inoperative. Rear windows and sunroof continued to work.
Initial investigation: Front left DCM failed first. Pulled and reinstalled fuse and functionality returned. Next day, right front DCM failed. Pulled and reinstalled fuse and functionality returned. Two days later, both DCMs failed. I could not regain functionality unless I pulled and reconnected the ground cable from the car's battery. Connected diagnostic system and device indicated an error on the CAN-Hi bus internal to the the car.
-W210 OBD2 connector does not have access to the CANBUS as do later models equipped with CAN D (data). With CAN D on the OBD2 connector one can hook up a breakout box and probe/monitor the signals on the bus. W210 requires a bit of improvisation.
-First, I purchased a used junction block with several CANBUS connectors off of Ebay. Remove the locking cage using jeweler's screwdrivers by using your thumbnails to pull the locking tabs apart at each end; the cage will pull off the side of the junction block. Remove a connector using needle-nose pliers, a small flat tip screwdriver, or your fingers. Do not attempt to remove the connectors by pulling on the wires as this will damage/destroy the connector. Strip a quarter-inch or so of insulation off of the ends of the wires.

-Next, pulled the X30/7 junction block from its location under the right front door sill. On the W210, ten of the eleven slots are used leaving one slot open for the diagnosis connector. Insert the diagnostic connector and attach multimeter. this photo shows the CAN Lo line in the "Sleep" mode.

-Important note! Do not swap connectors between positions! Each connector position corresponds to a schematic position. If you swap connectors, you'll be chasing ghosts as the schematic no longer matches! (Don't ask me how I learned this one, okay?) W210 CAN B schematic below.

-Positions 1 (LCP), 6 (left front DCM), and 8 (right front DCM) were failing. Following chart shows the voltages I obtained (inked in) compared to the expected voltages. CAN Hi was effectively at zero volts when asleep and, when awake, was at its sleep voltage. CAN Lo was good when asleep but, when awake, was almost at its sleep voltage. Asleep is with key off, Awake is with key in position 1.

- Pull and reinstall one connector at a time while monitoring CANBUS voltages. Nothing changed on positions 10 (PSE), 9 (right rear door), or 8 (right front door). When I pulled connector 7, voltage stabilized correctly for both CAN Hi and Lo when asleep or awake. Wait a minute...connector 7 is for the left rear door. That door never failed so what would it have to do with the rest of the CANBUS? With connector 7 removed from the junction block, I checked the connector for a ground to chassis; CAN Lo was good, CAN Hi showed a 95-ohm short to chassis ground. I pulled the door panel off of the left rear door (yes, have industrial adhesive available to glue parts of it back on because they will break off due to old age). I then pulled the connector to the door electronics, then back to the junction block and...no more short to chassis ground. (Thank God for that. I was not looking forward to possibly having to rewire a pair of CANBUS wires.) Reinserted connector 7 and CANBUS remained stable. Reconnected the left rear door connector to the door electronics and the CANBUS failed. Pulled connector again and all is good. The culprit is pictured below. Of all things, the electric window motor which is tied into the CANBUS via its electronics.

-The part, 210-820-53-42, is still available for ~$172. Purchased, installed, and all is good once more!

Hope this helps some other folks.

Interesting that the motor is tied in like that. To me that is a very poor way to have done it but it's awesome that you found/ fixed it.

bbirdwell, where did you source the two pin CAN connectors? I need a couple for something I am working on.

Found the splice junction on Ebay. There's one available there now for $30. Search in ebay motors for "mercedes wiring harness plug connector junction 0025467940".
Or use this ridiculously long address... Same seller from whom I purchased.
https://www.ebay.com/itm/18595296246...Bk9SR4qgk9GlYg

If you don't succeed, PM me your mailing address I'll drop one of the connectors into an envelope and mail it to you.

Thank you, sir! I really appreciate it.