I have a 1994 E320 non-ASR California car. 222k miles. The engine wiring harness was replaced with factory Mercedes harness by me over 7 years ago. 2 months back I replaced the ETA which was dead for almost a year. The car was driveable before but with no throttle assist when turning on the AC it was a safety/stalling hazzard. So with summer coming I replaced it with a used unit and all was good. Then about a week ago the car went into limp home mode. It starts and idles fine but will not rev past 1500 rpm. I checked codes (Arthur Dalton code reader) and got the following:

Pin 3: 17
Pin 8: 42,45
Pin 14: Cannot read codes, led is dim with no button push

This all pointed to the CC/ISC module N4/3 since I could not pull any codes from it. So I located another module, 124-545-55-32 and it is showing the same issue. I am assuming something along the path has a high resistance short to ground producing the dim led on pin 14 but I am not sure where to go next. I am thinking I can start disconnecting other inputs into N4/3 and see if I can get the dim led to go away. But I am not sure where some of the connectors are. Such as X81/4. It is listed in the W124 Electrical Troubleshooting Manual on StarTek but no location is given for it.

http://www.startekinfo.com/StarTek/outside/12264/Program/ETM/wire_plug.pdf

I will also be checking the OVP and diagnostic modules. Especially getting the info on which version the OVP is as I know these cause many strange issues.

So I am hoping someone might have an idea to help reduce my search. I have been Googling for hours with lots of information but nothing in my specific problem area.

Thanks,
David

I have checked the OVP and it is the later part number, 000 540 67 45. It is the genuine Mercedes part and the date code is 1999 so it has been replaced in the past. I did a diode check with a multimeter when it was disconnected. That looked ok. I also checked voltage across all the pins with it connected and key on and all looked ok.

In using the meter to check voltage on the DTC, I see around 12v for pins 3, 8 and of course 16. But pin 14 shows around 7 volts. I wish I knew how to bench test the CC/ISC module so I could pull codes with it out of the car.