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2001 Passat V6 Intermittently Won't Run

3K views 8 replies 5 participants last post by  Tomvw 
#1 ·
Ok, so a buddy of mine bought a front end wrecked 01 Passat with a V6 from an auction. We rebuilt the front end...mostly cosmetic damage. Have no idea the running history of the car before we bought it.

It will start and run great, then out of the blue shut down and won't start again unless we pull the plug for the MAF or fuse #34. Once we pull either of these, it starts right up and runs. If we immediately try plugging either back in, the car shuts off, but if we leave it running for a min or two and plug either back in, it will continue to run for an unspecified amount of time before it dies again. After dying, it throws many codes indicating many different sensors "shorted" or circuits open or low.

If we start the car with the MAF unplugged, it runs great but throws a code for the MAF being unplugged...obviously. If I plug the MAF back in it will run fine for a good long time...long enough to drive at least 5 miles or so. BUT, if I clear the MAF code, the car will immediately die. I have already replaced the MAF with a known good one...same results. It also doesn't make sense to either of us we can pull fuse #34 and the car runs great...but throws a ton of codes.

We're stumped. Need your expert help on this one!! We're about to douse it in gas and have a bon fire...

Thanks!
 
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#3 ·
With mutiple codes present, I'd start at the ECU box. Check the relay (if present) contacts, disconnect and re-connect all ECU connectors, using a contact cleaner spray on them before reconnection. Since I would expect the problem is an electronic connection issue, I would continue to remove, spray clean, and reconnect everything accessible, including the battery ground terminal at both battery and car body connection, positive cable connections, and so forth.
 
#4 ·
Check the fuel pump relay. It powers fuse 34, and if overloaded, may disconnect. Also start tracking everything that fuse 34 powers (quite a bit on the engine) and see if anything is shorted out.
 
#6 ·
Yeah, we've checked the FP relay...and replaced it. What's crazy is we can disconnect the MAF and car runs great, and only throws a MAF code...none of the other codes pop. Already tried replacing the MAF to no avail.

We're in AZ and in order for the car to pass emissions, CEL needs to be clear and all sensors need to be ready.

Really frustrating.
 
#8 ·
I think, eventually, you'll be "proving" that none of the wires leading to/from the MAF is grounded or otherwise broken. You need a Bentley (possibly Haynes?) schematic to determine where each MAF wire orginates/terminates. Once you know, each wire can be tested.

IIRC, fuse 34 also provides power (5V) through the ECU to the MAF heating element (MAF signal to ECU - mass air flow proportional to current required to maintain hot film [inside MAF body] at a given temperature...more air flow, more current required).

In essence, when your V6 is running, it's in limp mode (since no valid MAF signal).
 
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