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Old December 31st, 2015, 16:48   #1
Matthewsz
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Default Glow plugs don't work, new plugs, new harness, new relay, good fuses

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.
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Old January 1st, 2016, 07:16   #2
sisyphus
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What was the code, exactly?
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Old January 1st, 2016, 07:54   #3
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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.
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Old January 1st, 2016, 10:23   #4
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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.
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Old January 1st, 2016, 11:24   #5
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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.
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Old January 1st, 2016, 11:45   #6
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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.
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Old January 1st, 2016, 14:46   #7
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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?
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Old January 1st, 2016, 15:58   #8
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Quote:
Originally Posted by 9diesels View Post
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.
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Old January 1st, 2016, 16:40   #9
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Quote:
Originally Posted by AndyBees View Post
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...
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Old January 1st, 2016, 16:53   #10
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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?
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Old January 1st, 2016, 17:35   #11
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Quote:
Originally Posted by JDSwan87 View Post
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.
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Old January 2nd, 2016, 06:49   #12
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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).
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Old February 5th, 2016, 23:49   #13
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Quote:
Originally Posted by turbocharged798 View Post
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...
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Old February 6th, 2016, 09:45   #14
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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.
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Old February 6th, 2016, 09:51   #15
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Quote:
Originally Posted by sisyphus View Post
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.
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