Glow plugs don't work, new plugs, new harness, new relay, good fuses

Matthewsz

Veteran Member
Joined
Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
Hi forum members, I was wondering if any of you have experienced this before. The title says it all. 2003 jetta manual ALH. I had 1 bad gp code and decided to get a whole new set of 4 Bosch, new oem harness because the old one was coming apart, after this none of them worked. New harness wires tested, they should work. I tested the fuses at battery, unplugged the coolant temp sensor, still nothing (other than longer glowing light on the cluster). I've read the gp testing thread, even posted there, no answer. Got a brand new Bosch relay, still no power at the harness. No clicking heard from relay either, so my only guess left is the ecu... How could that go bad at the same time randomly?
Thanks for all the diys, helpful posts, I've been reading the site for years and it was time to post.
 

JohnWilder

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Joined
Jul 13, 2013
Location
Breckenridge, TX
TDI
2003 Jetta 5 spd manual
For what it's worth, I disconnected the power connection lead that feeds the glow plugs. I had to replace a couple of them and realized that it never gets cold enough here in Austin to require a glow plug to begin with. Everything works fine.
 

JB05

Top Post Dawg
Joined
Oct 20, 2005
Location
Il.USA
TDI
Golf,2005,anthracite blue
Are you measuring the pre-glow; ignition on, engine off? This only lasts ~ 23 seconds; so you would have to have your DVM set up so you can view it when you turn on the ignition.
The after-glow could be anywhere from 1 to 4 minutes, unless it is very warm outside.
 

Matthewsz

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Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
P0671
P0672
P0673
P0674

It's been pretty cold here, some mornings are at freezing point. The car needs more cranking and I get more smoke from unburnt fuel when starting.

Yes, ignition on, engine off, no power at the harness. In the relay 2 pins on both sides of the wide pin don't get any signal from the ecu.
A friend of mine just told me last night that he had the same problem, and he replaced the fuse box at the battery, that fixed it. Sounds interesting but I might have to try that.
 

AndyBees

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May 27, 2003
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Southeast Kentucky
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Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Without looking it up, a certain fuse in the box at the battery supplies power to the GPs via the Relay. The ECU sends the signal/current to activate the Relay. Thus, I cannot see how replacing the fuse box would solve anything........... unless there is no current available on the down side of the particular fuse for the GP Relay. I'd check that before replacing the entire unit.
 

9diesels

Member
Joined
May 16, 2014
Location
Wisconsin
TDI
2000 Beetle
Short GP timer

I live in WI. Even when it's very cold, the glow plug lite on the cluster is only on few a second or two. The car takes some cranking to start. I have a new temp sending unit installed. Is this an ECM problem?
 

Vince Waldon

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Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
I live in WI. Even when it's very cold, the glow plug lite on the cluster is only on few a second or two. The car takes some cranking to start. I have a new temp sending unit installed. Is this an ECM problem?
Best bet would be to start a new thread of your own for this issue, since the symptoms are different than the original posters and the solution(s) will be, too. :):)
 

Matthewsz

Veteran Member
Joined
Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
Without looking it up, a certain fuse in the box at the battery supplies power to the GPs via the Relay. The ECU sends the signal/current to activate the Relay. Thus, I cannot see how replacing the fuse box would solve anything........... unless there is no current available on the down side of the particular fuse for the GP Relay. I'd check that before replacing the entire unit.
Thanks Andy, I agree that it doesn't make much sense to change the unit. I will check all those wires and fuses again, but I know for sure that the wide pin is always hot at the relay.
Tomorrow we're getting started on pulling the v6 from my Passat, busy new year...:)
 

JDSwan87

Black Swamp Thing
Joined
Feb 9, 2014
Location
Michigan near Toledo
TDI
2001 Jetta TDI, 5 speed Lagoon Blue Metallic(sold); 2005 Jetta TDI Wagon auto
This may seem like a silly question but, if the ECU has a stored code for a GP fault, will it shutoff sending power to that GP? OP, have you cleared the old faults?
 

Matthewsz

Veteran Member
Joined
Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
This may seem like a silly question but, if the ECU has a stored code for a GP fault, will it shutoff sending power to that GP? OP, have you cleared the old faults?
Yes, codes were cleared several times with torque app and vcds as well.
 

turbocharged798

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May 21, 2009
Location
Ellenville, NY
TDI
99.5 black ALH Jetta;09 Gasser Jetta
Fuse #2 on top of the battery is what gives power to the relay. Check to see if you have power coming from that fuse into the relay(should be a thick red wire).
 

Matthewsz

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Joined
Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
Fuse #2 on top of the battery is what gives power to the relay. Check to see if you have power coming from that fuse into the relay(should be a thick red wire).
Yes, that must be the wide pin at the relay that's always hot.
I got an ECU from the junkyard, same year, same part number but wagon alh tdi. It didn't make any difference, or is that because of the immobilizer, would that block the ecu sending the signal to the relay?
At this point I tried everything, no idea what's going on. Broken wire from ecu to relay? Kinda doubt that...
 

sisyphus

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Dec 8, 2008
Location
Appleton, Maine
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99.5, '01 A4 Jetta sedans, 5 sp box, Hamman mod, Joey mod, Bilsteins, 2.00" lift
In the OP, you say you had one bad GP, so you replaced them all along w/ the harness. After that nothing worked.
You should go back and check your work. It's not logical that after replacing the harness along with the other three GPs that none of it should work. It must be something disconnected accidentally or incorrectly somewhere.
Troubleshooting electrical symptoms should always include an element of self-doubt.
 

fruitcakesa

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Joined
Feb 18, 2007
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Vermont
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04 jetta 5 spd wagon
In the OP, you say you had one bad GP, so you replaced them all along w/ the harness. After that nothing worked.
You should go back and check your work. It's not logical that after replacing the harness along with the other three GPs that none of it should work. It must be something disconnected accidentally or incorrectly somewhere.
Troubleshooting electrical symptoms should always include an element of self-doubt.
Truer words;)
 

Matthewsz

Veteran Member
Joined
Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
In the OP, you say you had one bad GP, so you replaced them all along w/ the harness. After that nothing worked.
You should go back and check your work. It's not logical that after replacing the harness along with the other three GPs that none of it should work. It must be something disconnected accidentally or incorrectly somewhere.
Troubleshooting electrical symptoms should always include an element of self-doubt.
I agree that it's not logical.
Testing with a multimeter everything's fine. The relay isn't even activated, no sound or signal comes out of it. Checking all the pins on the diagram only 2 of them are not working and they both go to the ecu. That's the only thing I didn't check, the wires from ecu to relay. I'll test those and report...
 

gatz

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Oct 29, 2005
Location
Windsor, CT
TDI
2005 Mk4 Golf TDI PD, 2006 MkV Golf GTI
Just to note the glow plug controllers are not relays, they are pulse width modulated electronics. They don't click.
 

Matthewsz

Veteran Member
Joined
Aug 9, 2015
Location
San Diego
TDI
06 Jetta, 09 wagon
double check the connector in the wiring channel, make sure it's all the way seated... also make sure you did not accidentally cut the wrong harness when snipping wires ;)
Thanks, afaik there's only 1 connector in that channel, and I watched a video of the process so can't be missed... I can get the multimeter signal from the glow plug control module all the way to the harness, so that's not the problem:)
 

Ol'Rattler

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Joined
Jul 3, 2007
Location
PNA
TDI
2006 BRM Jetta
P0671
P0672
P0673
P0674

It's been pretty cold here, some mornings are at freezing point. The car needs more cranking and I get more smoke from unburnt fuel when starting.

Yes, ignition on, engine off, no power at the harness. In the relay 2 pins on both sides of the wide pin don't get any signal from the ecu.
A friend of mine just told me last night that he had the same problem, and he replaced the fuse box at the battery, that fixed it. Sounds interesting but I might have to try that.
Plausible. Due to that fuse box sits directly on top of the battery on the MK4's, battery fumes cause corrosion over time. On my Gasser MK4, the corrosion got bad enough to cause high resistance/overheating and actually melted part of the fuse box and some wires.
 
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