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2002 Jetta -- MIL and Glow Plug issues

7605 Views 9 Replies 4 Participants Last post by  jeeperhdbmw
Fellow TDI enthusiasts,

I have a 2002 Jetta TDI with roughly 165K miles on it. Recently, the MIL came on indicating a faulty #4 glow-plug. I decided to replace all glow-plugs at once with these: http://www.dieselvw.com/LateGlowPlugs.htm. This solved my problem for about 3K miles and then the light came on again. I checked the #4 glow-plug and yeap, it was bad. I replaced it once more and this time the MIL stayed off for about 1K miles; again, #4 showed bad. However, this time when I tested it with a light hooked to the positive battery terminal, the #4 showed good. Any suggestions? Could I have a bad glow-plug harness or relay? Is there some unseen issue with the #4 cylinder that is causing this? Would OEM glow-plugs make all the difference; if so, why is the problem only with #4? Any and all assistance you can provide to this "driving me crazy" issue is greatly appreciated.

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It's possible the harness is bad. The contacts in the tips can corrode and fail. Just replace the harness.

Oh, and the parts linked through that site and all the similar copycat sites are almost certainly all very low quality parts. I don't think OEM parts would help vs genuine Bosch glow plugs but either would be an improvement over those crappy parts. More likely is a bad glow plug harness.
Even if those glow plugs worked, you can get a new set for Bosch or Beru for about $50. Get rid of those glow plugs, they are junk. If you're lucky they will work fine. If you're really unlucky they could break off in the head. Although the serivce manual says to keep them all the same brand and not mix match them, it'll work fine and no problems have even been reported by mixing them.

Test each glow plug with a multimeter and resistance should be relatively consistent within each one. They should all read about .5-1.5 ohm and each should be within .3 ohm of the others.

You can test the harness by testing voltage on each plug. Have a helper turn the car on and you should get about 12 volts for the glow plug duration and then see it drop.

Other than that, the fuse, relay, or wiring could be bad.
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Sorry it took a while to respond, I'm in the military and have been away from the computer for a while. Thanks for the advice and tips. I'll throw out the cheap plugs and replace the harness to see if that solves the problem. With a 165K relatively trouble free miles, the Jetta could use a few new parts. Thanks again and take care.


I've got the new BOSCH glowplugs and a new harness. Before I start digging around to replace the harness, it there a good site that explains this process? I love this forum for all the tips and the step-by-step instructions, but I didn't find anything outlining the best procedure for replacing the harness. Thanks again for all the imputs.

Here is an article on how to replace the glow plugs:


The harness is visible. Take it one step further to replace the harness.

First blow out any dirt around the glow plug hole. Use a 10mm deep socket to remove the glow plugs.

Does your new harness have more than 2 wires and a plug? I believe the 2002 and newer do but the plug is deep in. The older ones had only 2 wires because they couldn't sense individual glow plugs.

If you just want to cut/splice in the new harness, I suggest using crimps instead of soldering because it's much faster and easier to get a good connection. Cut the old harness to leave a long wire on the harness end so you have something to work with. Follow up with heatshrink tubing to make a waterproof connection. That's it.
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Replaced the plugs and harness yesterday. Started to replace the whole harness, but after seeing the spiderweb-like routing of the harness and that gunky tape that was wrapped around it, I decided to do the splice. Seems to be working just fine.
Just completed 5,000 miles after harness change and have had no problems. I got the harness from metalmanparts.com for $55 and can't be happier to have that MIL out! Next on the to-do list is intake cleaning. Take care.

:thumbsup 5,000 miles already? You really do need a TDI!
We sure do. It's our runabout car and my wife just went to CA and back from Abilene TX.
I love the TDIs so much that I'm really tempted to sell/trade in my 04' BMW 530i for a new Jetta TDI. In fact, I'd like to consolidate by getting rid of the Jeep, Harley, and BMW and just become a VW TDI family. But my wife won't let me. How's that for 180 degrees out from the norm?
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