PeachParts Mercedes-Benz Forum - View Single Post - '05 CDI "communication fault" N14/2 Glow Output Stage 2538-4 jay-bob?

jay_bob · #11 12-23-2022, 08:07 AM

Remember that the path for communication to the ECU goes like this:

OBDII port -> ZGW (Central Gateway) -> Engine CAN bus -> N3/9 ECU

And from the ECU to the N14/2 Glow Plug it is a LIN bus that leaves the N3/9 ECU and goes to the N14/2 Glow Plug and the G1 Alternator regulator.

So we have 2 things that have to work.
First the scan tool has to see N3/9 through the central gateway via the Engine CAN bus.
Then assuming it can see N3/9 and communicate with it, then the LIN bus has to be operating for the N3/9 to communicate with N14/2.

You can't directly talk to N14/2 with the scan tool, you can only get get N14/2's status as N3/9 has determined.

So if the LIN bus is down then you're not going to see the N14/2.

Another thing to try: get in, close the door, put key on position 1 (just the radio on).
Navigate to the MPH display on the cluster.
Push in the dimmer knob 3 times rapidly, you should see Ub = 12.xx V
Start the car and watch the voltage. If it immediately goes to 14.x V then the regulator is not communicating and it's in default (make nominal voltage all the time) mode.
If the voltage walks up from 12.xx to 14.xx over the span of about 15 seconds then it is getting orders from N3/9 to walk the load in. Meaning the LIN bus is working.