Glow plugs 3&4 not working

I have a 02 Jetta that I recently bought. Glow plugs 3&4 were not working so I replaced the glow plugs and the wiring harness. I have cleared the codes and it doesn't start well in the cold and codes for the glow plugs 3&4 continues to come up. Is there something wrong with the control module? The glow plug light seems to stay on the proper amount of time, I have had another TDI so I know how they should start. Thanks

Did you replace all the glow plugs or just 3&4? If you only replaced 3&4 you probably replaced the wrong ones because the computer numbers them backwards

http://forums.tdiclub.com/showthread.php?t=278188

^^ this.... the number one gotcha of glow plug repair.

I replaced all 4

Darn it... t'was a great theory.

Have you found the "Glow plug 101 V2.0" thread? Tons of troubleshooting info there.

Does the control module go bad and only send power to a couple of glow plugs?? I know the harness has multiple wires which I assume are for the individual glow plugs. So I guess I need to test to see if there is power going through all of the wires.

There are two wire glow plug systems (power is shared between pairs of plugs) and four wire systems (each plug gets its own power)... don't remember when the switch-over year for Beetles was, although if you got a 3/4 error code you likely have the two wire system.

Either way, it's worth tracking down the master thread: it has all the details, good pictures of the individual components, etc.

Any part of the system can fail, so you pretty much have to take a step-by-step approach to troubleshooting, as replacing parts can be expensive.

2002 has the 4-wire system, so each plug is reported separately.

Don't forget the glow plug "relay" under the cowl.

I say "relay" with quotes because it's actually got a little circuit board in it instead of the usual mechanical relay bits...

I would go after the glow control unit (relay) in the cowl... check the wiring and connector first, for rodent or water damage.

If you do not find anything, put a new one in and see if that fixes your problem.

Update on my glow plug problem. The glow plugs I installed came with my car, they were some off brand that I never heard of. The reality is OHM's don't lie, two of them were junk (open). I replace those two with two used ones I had from my other TDI. The car started good. I have some on order. Thanks

I tried the Autolite ones for a while, had 3 cooked to death in a year (including one after replacing the glow "relay"). Ended up pulling them and putting a full set of Bosch in.

Stick with either Bosch or Beru for an ALH.