2004 C320, M112.946

Vehicle fails to crank, unable to communicate with ME control unit using a scan tool.

Five blocks of wiring connectors are present at the top of the control unit, numbered 1 to 5, front to back. The first block presents with 9 numbered pins connected to a single wiring harness plug connector. Removal of the plug reveals a smokey grey discoloration surrounding pin #5.

Any information as to what circuit is served by this pin?

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Connector 1 and 5 appear to be identical?

If its connector #1 pin 5 its the main power feed for the ECU. Circuit 30, should be hot at all times.

If it’s connector #5 it’s the coil driver for cylinder 4a.

Connectors are numbered 1 through 6, starting at the far right and moving left.

In this case, we're looking at damage on pin 5 in connector block 1. Pin 5 is a power supply pin. Currently the ECU is off line. Don't know if the unit is damaged internally.