Glow plug light turns off right away after ignition in on position.

My glow plug light turns off right away when I turn ignition to the on position when 16 degrees out. It's been doing that for a week now. Car is very hard to start. I noticed relay with 50A fuse strip on fire wall is melted. I think it's the coolant glow plug relay. Could that be problem. Also glow plug hard plastic harness doesn't look so good. Lots of cracks. Is that common. ANY help is appreciated. Thanks.

I would post a couple pics but not sure how to do that...

replace that 50a fuse strip, should get it working. although if/you may blow another strip, in which you would have to trace that down.
look in the for sale section, you can also post, for replacement harness, etc. i sure there are members who have parts that can help.

Strip fuse under the hood is for coolant GP's and not the engine GP's. A melted fuse will probably mean there is a bad coolant GP somewhere or more than one. There are three of them in that system. These are not monitored so a failure will not be reported to the ECU.

First thing I would check is whether you have a good 50 or 80 amp maxi fuse under the dashboard around / above the fuse box. Consult the sticky thread about fuse boxes and GP stuff for clarification. The harness at the GP's could contribute to a bad situation but don't even know if power is getting that far yet.

You will also need to determine which GP system you have. There were a couple different designs but I will bet that you probably have a 103 relay in position #12 of the relay panel, but I could be wrong. If you don't that's fine but if you have that relay in position 12 it will add another component to check.

At this point it's all I have to offer but I would suggest going and reading about the different fuse / relay panels in the sticky section of the Mk3/B4 forum, you will see it two thirds of the way down. There are pictures in there also that will help you.

If you can find your maxi fuse we can move on from there.

It will be hard starting in 16 degrees with no GP's at all.

Steve

Also check you Coolant temp sensor. If you unplug it, the system will think that it is say minus 60F outside and give a long glow plug time. If the CTS is shorted to ground, you will get glow times suitable for an 80F day.

^^^ this, had this issue, it was shorted out!

Just to clarify, the coolant glow plug system (three glowplugs on the head water outlet, fuse on firewall) are there to improve cabin warm-up times and not related to your cold-start issues.

In terms of your cold start issues, yup, it sounds like the glow-plug side of the coolant temperature sensor (the other side runs the temp gauge on the dash) might be lying to the glow plug relay, and as posted above the quick test is to unplug the CTS and see if the glow plugs then stay on for 15-20 seconds.

If that is the case, the CTS is highly suspect... and they're cheap.

If the light still only stays on momentarily then the glow plug relay is the chief suspect.

On mine, the fuse was blown, but the light would stay on for a while anyway as if it was working normally, so although the fuse could be blown, there is some additional problem, probably like others said, the CTS or relay.

I wasn't aware that the the CTS could fail in a way that would cause a 'high temp' situation. Indeed that would fool the GP relay into thinking that no preheat was needed....you learn something new every day.

I'd still look at the fuse but definitely do the CTS test to begin with since that's the easiest to perform.

Steve

Ol'Rattler said:

Also check you Coolant temp sensor. If you unplug it, the system will think that it is say minus 60F outside and give a long glow plug time. If the CTS is shorted to ground, you will get glow times suitable for an 80F day.

Click to expand...

Coolant temp sensor failed for me with the same short GP light symptom. Says the coolant was 75*C in -3*C weather.
Watch out for Chinese crap. Thought that I had a spare sensor and found it would not even fit in the hole. How does this stuff make it to the marketplace?

Because we allow it. People get so pumped when they get a bargain, so they buy Chinese. Multiply that by a whole crap load of people that do't realize they are buying sub standard parts.

that easy to find,&get stuff, like from autohausaz, like that meyle is sub-par. also is the febi junk. china made i believe. not complete junk, but buy better quality, will work out better, and for longer.