engine code - Glow plug circuit malfunction

I had a check engine light on and I read the code off of the engine and it said "Glow Plug Circuit Malfunction" Does this mean I need to replace my glow plugs or clean something? 99.5 Jetta TDI

Thank Jim

I had this problem with my 2001 TDI and had brought it to the dealer several times for repair. Replacing individual bad glow plugs did not resolve the problem. They replaced the harness, fixed grounds and still the problem persisted. Their ultimate fix was to replace the harness (apparantly has been updated twice) and all 4 glow plugs. It has been a while since the light has come on and I am thankful that the dealer was willing to work with me on this issue.

I'm not sure, but, I think it's against forum rules to use the term "thankful" when describing opinions about dealers. /images/graemlins/wink.gif

Glow plug malfunctions are a rite of passage for tdi owners. There are lots of threads on the subject. Basically it is probably either the glow plugs or the harness. Check the glow plug resistances and if they differ much, replace them. They are around $20 each online and as easy to change as spark plugs. My plug resistances were 0.5, 0.5, 0.3, and 0.5. I replaced mine, cleared the code and the CEL went away. Others find they have to replace the harness. There are threads that give instructions on that. It's apparently not too hard, but harder than changing glow plugs. Do a search and you should find a lot of information.

Ok so I'm looking at buying glow plugs there is a 10mm one and a 12mm one the 10 says its for vehicles without glow plug heater and the 12 says its for vehicles with glow plug heater and ideas which one I would need?

thanks

Jim

You need the 10mm plugs. The 12mm plugs are coolant glow plugs. They are only installed on Manual transmission cars and are not monitored, so will not cause a MIL. I suggest testing them first to confirm or rule them out as the cause of the problem. But with the age of your car, it is not a bad idea to replace them anyway since it is almost 5 years old. Harness replacement is also not absolutely necessary either. The harness can be treated with a deoxidiser & contact cleaner/enhancer. For more info on testing the glow plug system & products to traet the harness, look here.

when we had this problem, the "bad" glow plugs was just a melted coolant plug harness.