I've searched dozens of forums and posts and have yet to find a good diagnostic procedure for isolating the cause of this vehicle's problem.
Vehicle is a 2001 Jetta Wolfsburg with a DL ECM, 1.8T, 5-spd. Vehicle will turn over but not start. Fuel pump (relay) is non operational. I didn't have VCDS with me when I first encountered the problem so I used a standard OBDII reader and it wouldn't connect to or read the ECM.
Originally I checked all fuses with a DVM and reseated the fuses associated with the ECM. Checked the output of the power relay (428 - wh/or wire) and there was no voltage. The relay was not activating. During testing, the fuel pump relay started working again, but the ECM power relay did not. I suspected a bad relay and pulled it, but also removed the ECM at that point to check the part number. All connectors, pins and wiring were clean and in good order. The ECM sat in my garage for a day.
After reinstalling the ECM and power relay, I reattached the positive battery cable. The fuel pump relay worked and the car started and ran fine. Pulling the power relay caused the exact same no-start symptoms as before. A new OEM power relay was installed. The standard OBDII reader would also now read the ECM.
The car ran fine for two days. After sitting for an hour in a parking lot, it wouldn't start. No fuel pump, standard OBDII wouldn't read again. I checked the output of the ECM Power Relay and this time it had 13VDC. The engine tried to fire initially, indicating the ignition system is indeed receiving voltage from the ECM power relay.
I connected my laptop with VCDS and auto scanned. The engine address shows a 17069 code - ECM Power Relay Control Circuit (271): Open Circuit. Ross-Tech's wiki provides possible solutions as "Test voltage supply to ECM, Check wiring and fuses, Replace Faulty ECM Relay (J271). All modules show a low voltage code because the battery was disconnected. No other pertinent codes registered.
The real problem I'm having is the factory manual is less than user friendly in trying to follow electrical paths from component to component. It appears the fuel pump relay activates from pin 65 on the ECM. If this is correct, and the ECM relay is working properly, then could the ECM actually be at fault? Seldom in 30-years of working on cars have I ever found wiring to be the issue unless it's actually damaged by melting, rubbing or rodents. Or extreme age. Occasionally stupidity. The wiring in this vehicle appears to be in very good condition.
The temperatures have dropped significantly over the past month so one test I'll do is to heat the ECM enclosure with a hair dryer to see if it might have an electrical intermittent. I'm also working to source a good used ECM now.
If anyone has any specific tests or helpful information, it would be very much appreciated. I'll be sure to post all results of what I find. Thank you.