code P0684 Glow Plug Control Module

Hi can anyone tell me what I should look for to fix this code ( P0684 Glow Plug Control Module to PCM Communication Circuit Range/Performance) I replaced the temp sender and the glow plugs are all ok and working. If I clear the code its keeps coming back 02 jetta 5sp

Somebody must of had this code somebody HELP!

Personally, if the car runs ok, I would ignore it.

Else I would consider the harness or a new relay.

It is saying the ECM is not communicating with the relay. The relay on your car is near the ECM, in the plenum (that area at the base of the windshield with the plastic cover). You might investigate the relay socket for corrosion. Just unseating and plugging the relay in might sort things out. Otherwise, you probably need to replace the relay.

[SIZE=+1]I check for a relay in the plenum didn't see one I think that my car has this unit under the dash I had to replace a glow plug control unit there when I first bought the car it was missing My concern is that the glow plugs were not firing long enough but I checked this out my glow plugs stay on for about 10 to 12 sec what was confusing me was that the light was only on for about a sec or 2. I checked this with a test light the glow plugs are still on about 8 to 10 sec after the light goes out. I still don't know why I keep getting this code but I will keep working on it. [/SIZE]

You must have one of the few early '02 cars with the same GP system as the previous years. That relay (marked 180) is the module that the ECM is having a problem talking to. Make sure it is fully seated in its socket (as a first step). If that doesn't work, take it out, and if you're handy with electronics you might open it up and verify all the soldering connections are good. If you're not handy, replace it.

Your last post said the module was missing from the car? Was the check engine light on when you got the car?

Later '02 cars have the GP relay in the plenum near the ECM (unless it is missing ).

[SIZE=+1]When I got the car it was in the summer as soon as it got cold I got a check eng light the code said the module was bad when we checked it it was missing we put in a new one under the dash I know it was not a 180 it was a 451 452 something like that and it was fine for about a year or so but I started to get a check eng lights again I don't think it is the same problem . The glow plugs seem to be working ok but the car seems to be starting harder then it used to but it has 156K on it now. I haven't been able to work on it for the last few days I have been out of town to a serve school I have a friend that works for a VW dealer that is going to run the problem by some of the tech to see if they have any ideas. When I get back I will look for the relay marked 180. Thanks for the input[/SIZE]