TDI Glowplug heater circuit code

[theman53]

I have replaced the glowplugs and harness and GP relay. When it is cold, 10f or below, and the car doesn't start immediately, I get a check engine light. The harness needed replaced as it was cracked and the code used to say "intermittent glow plug relay" so I figured replace the relay and all would be good. It hasn't. If I have to crank the car longer than 2.5 seconds to get it to start, the light comes on every time.

Any ideas what could be going on? How to get it to quit coming on? Car has started and ran fine up to about -5f, but the problem persists.

2001 jetta ALH engine.

[410]

The coolant temp sensor can cause intermittent issues.  I've changed a number of them and it's only $15.  If you have some kind of a scan tool, check engine temp in the morning compared to air temp.  They should be really close.

Also make sure you have power at the gp's when you first turn the key on.  If no power, check the gp fuse on top of the battery.

[745 turbogreasel]

Whats the code now?
If it's for a specific plug, some  ALH have the #s reversed in the ECU which is  misleading.

[theman53]

mine has the older harness with only 2 wires. Code IIRC was P0380 glow plug heater circuit a

[410]

Double check all your connections.  There's also a really good troubleshooting guide on tdi club that should narrow it down for you.

[the caveman]

Are you sure all the GP's are the same brand? All 4 must be either Beru or Bosch, not a mix of the 2. Take an ohmmeter and check the resistance of all 4, They must be less than 1 ohm. Also it doesn't hurt to put a little die electric where the buss bar contacts the GP

[theman53]

All are bosch. I will check it as soon as I have time.

The only time it does it is when it doesn't fire immediately, which is weird to me. I think if there is an issue it should do it all the time.

[the caveman]

The reason that a GP problem will set a CEL after starting is because the ECU fires them up after the engine starts to smooth out the idle at cold running[even warm actually].When it's cold the relay sends a pretty high amount of current to start the car, but then a lesser amount once running, that's why the DTC will come on when the ECU reads a difference of 2 amps between any 2 or more GPs.It is driving less current,therefore more sensitive to the output load. Like I said check the resistance of all 4, they must be all within .5 ohms [if I remember right]. I do know that Beru's are much more reliable then the Bosch's.I know it's stupid, but if possible you may want to switch out a set of Beru's if at all possible.Also when replacing the buss bar, did you cut and crimp the wires, or replace it right up to the 32 pin connector? If you crimped, every single strand of wire from each one must be connected.I have kinda given up cutting and crimping if possible.More time involved, and it can be be a pain to pull the old connector out, but will have better results.

[the caveman]

I just saw that you have an A4. Those models are notorious for having poor grounds. If everything else checks out, you should think about renewing all ECM related grounds. Near the ECM in the plenum[be careful removing and reinstalling the cover. It clips into the bottom of the windshield, and if both edges are not perfectly clean, you could crack the windshield], there is a terminal with at least 2 grounds with loop ends. Also under the battery and battery tray there will be at least 5 or 6 other loop end grounds in 2 spots. Remove all, clean with sandpaper or wire brush, then brake cleaner or alcohol and then apply a little dielectric grease. You can even do the big starter/battery ground that attaches near the other ones under the tray and where it attaches to the transmission bolt.This affects gassers more, but I have solved many mysterious issue by addressing those ground connections

[theman53]

Great stuff. I will check into it when I have time. Right now I am recovering from a big trade show that we had 40+ hours in 3 days. I have 4 ok used bosch glow plugs I can swap but none of the beru brand you have had luck with.