2008 E 320 CDI - Sudden Control Unit Failure?
 

2008 E320 CDI, 75K miles

Vehicle started readily yesterday, sits overnight and then today the engine fails to crank. Two separate ignition keys are tried, each is recognized by the ignition switch, each turns readily but the engine remains silent. The battery is fully charged. If the key is left in the "On" position for approx. 5 seconds, the engine's electric cooling fan activates at maximum speed, even though the engine is cold.

Fault code check reveals:

ETC – Electronic Transmission Control

Event C100 – No CAN message was received from engine management control unit.
Event D10B – No CAN message was received from engine management control unit.

ABR – Adaptive Brake

Event 4759 – No CAN message was received from engine control module.

Event 4840 – No CAN message was received from engine control module


Driver’s SAM

9040 – Component N10/1kO (fan relay module) is defective or not installed.

Event 9090 – Fault in CAN communication with control unit OCP.


SCM (MRM) – Steering Control Module
9348 – No CAN message was received from engine control module.

RecETR-LF-left front reversible emergency tensioning retractor

Event 5024 – Fault in CAN comm with control unit ME motor electronics.
Event 5025 – Fault in CAN comm with control unit ME motor electronics.
Event 5024 – Fault in CAN comm with control unit ME motor electronics.
Event 5025 – Fault in CAN comm with control unit ME motor electronics.

RecETR-RF- Right front reversible emergency tensioning retractor

Event 5024 – Fault in CAN comm with control unit ME motor electronics.
Event 5025 – Fault in CAN comm with control unit ME motor electronics.


ASSYST – Active Service System
9204 – Control unit ASSYST is not receiving any messages from the engine compartment CAN bus.


Possibly related to this situation - or not - the vehicle was serviced the day prior for several CDI5 (Common Rail Diesel Injection) faults:

* 2513-1 Component M55 (inlet port shutoff motor); positioner signals fault.
* 2531-2 Component M55; positioner signals fault Y.
* 2520-1 Component R48/1 (thermostat); short circuit to positive.
* 2502-2 Component R48/1; short circuit to ground.
* 2520-4 Component R48/1; signal line is interrupted.
* 2520-8 Component R48/1; thermal overload of control module N3/9 (CDI control unit).


Of merit was that with the engine cold, the fault codes could be cleared, the ignition turned on and fault codes rechecked, and with a stone cold engine the thermal overload of the CDI would still be reported.

Renewal of the inlet port shutoff motor was deferred but the "thermostat" was renewed, which cleared all of the R48/1 fault codes.

The vehicle was test driven after renewal of the vent line heater line (R39/1) and cleaning of the thermostat temp sender; the engine started readily and no faults were noted other than the lack of performance and "Check engine" light related to the faulty port motor.

Is the no start situation possibly related to the "overheated" CDI control module (whose fault code has not reappeared since cleaning of the thermostat temp sender and renewal of the vent line heater) ... or is the no start related to another control unit fault?

Thanks for the help.

Driver side SAM is malfunctioning. Very common failure.