Glow plugs 101 ***Ver. 2.0***

sed11

New member
Joined
Oct 30, 2005
Location
Chattanooga, tn
TDI
2003 jetta
So you are saying my engine must be worn out, cause it will
not start even at 70 deg. without major grinding on the starter motor. It starts perfect with temp sensor unplugged. I have a friend with a 01 golf & his stay on for about 10 sec.s {engine cold} no mater what outside temp is. How long does your lamp stay iluminated??
 

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
So you are saying my engine must be worn out, cause it will
not start even at 70 deg. without major grinding on the starter motor. It starts perfect with temp sensor unplugged. I have a friend with a 01 golf & his stay on for about 10 sec.s {engine cold} no mater what outside temp is. How long does your lamp stay iluminated??
Check your timing. Retarded timing makes it difficult to start the car between about 40*F & 50*F. At those temps, the plugs do not activate, but the ambient temp is cold enough to delay the ignition.

Read DBW's post about clod starts. Its a sticky at the top of this forum.
 

STRANGETDI

Veteran Member
Joined
Sep 20, 2001
Location
East Hampton, CT
TDI
2013 Audi A3 S-Line Premium Plus Quattro - APR Stage II
Here is why I replaced my harness:





I don't know what happened to it but I saw it as a problem.
Something either got fused to the harness or something melted through.
 

oNNoZeLe

Well-known member
Joined
May 14, 2003
Location
Netherlands, that Europe next to germany
TDI
Golf, GLS, aut. tans, 2000, blue'ish
i read your 101 and think it is perfect.

I went to get my car back from the dealer that supposedly cannot fix my 16764 P0380 error.:eek:

I have already had some discussion with the director of this company but it seems that he doesn't take care/time for his customers.:mad:

So now i got my car back and read the 101, i hope, think:D that i am gonna solve this problem myself and report this to their boss's boss. And will state that that company is not able to fix problems but the customer can.
Also some other issues but won't bother you with that.

One question i do have is: do i need to, except from the coolant GP's, keep other things in mind because i am driving a Automatic GLS TDI 2000 Golf..
 

vasillalov

Member
Joined
Apr 25, 2005
TDI
TDI, 2003, Reflex Silver
This DIY is great. I used it to identify and repair a malfunctioning glow plug on my girlfiends TDI.

Everything was easy! The CEL told me that I had a bad glow plug on cylinder #4 but my digital voltmeter told me its actually cylinder #1. The reading was 142 ohms and the other three read 1.1, 1.0 and 1.0 respectively. So I guess wingnut is right about something else too: the numbering is reversed on 2002 and later models. MY GF has a 2003 Jetta TDI GLS.
 

blthomas

Well-known member
Joined
Nov 23, 2005
Location
Culpeper, Virginia
TDI
00' Golf GLS
Just wanted to say this DIY is great.

I just used a friends VAG-COM to pull the generic code on my 00' Golf. I was sweating it because my manual is not here yet (bought it on ebay a couple days ago) and I wasn't sure if this was a dealer worthy trip. I have no VW/Audi shops in my town.

This kicks ass, I'll be working on it tonight thanks to you guys.

Thanks,
Blair
 

Wienand

Member
Joined
Sep 20, 2004
Location
Ithaca NY
TDI
Jetta, 1998, dark green
So, where can you buy a glow plug harness? does it have to be from the dealer - I've searched on line, and can't find anything.
 

STRANGETDI

Veteran Member
Joined
Sep 20, 2001
Location
East Hampton, CT
TDI
2013 Audi A3 S-Line Premium Plus Quattro - APR Stage II
I have to say, I have had absolutley no starting issues since replacing my harness (see above posts). Today and yesterday it was in the single digits, very cold, and she fired right up. Last winter, I would have have to crank for about 7-10 seconds.

Replacing the harness my be a way to troubleshoot the hard cold starting issues that people have. Over time the harness gets corroded, so maybe after 5 years or so, one should replace it anyway.
 

cha$e

Well-known member
Joined
Feb 9, 2001
Location
US
TDI
2010 Jetta
Thank you for the wonderful walkthrough. I have two questions:
1) In a nutshell, I've done all of the above and the CEL is still on. I have a 99 Jetta IV, and my CEL has been on for probably 3 years with the P0380 code. First I had the dealer replace the #1 plug and the harness. Since then I've replaced all 4 plugs, replaced relay 109, and twice replaced the glow plug relay. One time, the light stayed off for about 3 months. The second longest was about a week. Aside from that, it comes on EVERY OTHER TIME I start the car, about 30 seconds after ignition. Any ideas?
Side thoughts: When I check the voltage of the plugs (just did it a couple minutes ago) I have my digital meter set to 200 Ohms, and I tend to have to press the leads really hard into the plug/block in order for the resistance to drop down to 1.1. It's currently 1.1 on all 4 plugs and the 3 coolant plugs as well if I push down hard. I have sprayed electric parts cleaner on all 7 plugs and into the harness. I also tested voltage on the red wires atop the battery (by the extra three fuses) and get approx 12 volts in all cases. I have verified voltage coming out of the harness immediately after ignition. Finally, I have cleared the code using my VAG-COM, but it always comes back two starts later. Please, any suggestions?
2) Went to the dealer for an unrelated problem (Tom Wood VW in Indianapolis) and explained the above. I said I don't want a scripted answer, please investigate thoroughly and tell me why the CEL is always on w/ code P0380. By the way, I will say that the guy was an absolute jerk. I told him that I had read the code myself and he said "okay, well we'll take it in back and check it out with *proper equipment*". That just really bugged me - the bits flowing out of the OBD port are the same whether I'm using a VAG-COM or anything else. Anyway, at the end of the day, the response I got (in addition to needing a new N239 valve, which as of right now has not yet been replaced) was that the CEL was on because the COOLANT glow plugs need to be replaced. Now...it says earlier in this thread several times that the coolant glow plugs can't cause the CEL to come on. So, the diagnostic that I paid $80 for was completely bogus. Can anyone recommend a way to get my money back? I do have in writing that they say it's the coolant plugs...is there any "carved in stone" source that they'll respect that says that the coolant plugs can't cause the CEL to come on? I looked in my (paper) Bentley manual but couldn't find any such verbiage...
Thanks!
 

cha$e

Well-known member
Joined
Feb 9, 2001
Location
US
TDI
2010 Jetta
To clarify the "EVERY OTHER TIME" business above: I meant it comes on every other time I start the car, if I clear it every time it comes on. In other words, it comes on, I clear it, restart, it doesn't come on, restart again, it comes on again. If I don't clear it again, of course it will come on every time I subsequently start the car.
 

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
Wow. It seems that you have done almost everything needed to cure the code, yet it is still there. I have a question. How long ago was the harness changed by the dealer. You mentiened that the code has been present for 3 years. Was that when they changed it? If so, thats plenty of time for the harness to develop more oxidation. I would also suspect a bad connection at the splice point. What I would do is redo the splice to make sure there is a good clean contact surface and instead of using an electrical contact cleaner, pick up some Deoxit D5 to spray into the harness terminals. It is a contact cleaner, but also a deoxidiser. It will react chemically with the oxidation to remove it. A much better product for this application. Normal contact cleaners do not do this. For $15, its worth a try.

As for the coolant glow plugs, I can't reference you to anything that you can use to fight the dealership. I can just speak from my own experience where I unplugged my coolant sensors and the light did not go on. This is th easiest way to determine if they are monitored. But in your case, you need to clear the code and have it stay off before you can try that trick. Maybe someone with more knowledge of the wiring diagrams in the back of the Bentley can chime in as they wil probably indicate that the coolant plugs are not monitored?

Good luck and let us know how the Deeoxit works out if you decide to rey it.
 

Venturabass

Veteran Member
Joined
Jun 24, 2004
Location
Stonington, CT
TDI
2001 VW Jetta TDI GLS, tornado red, 5spd
Wingnut, first off, great post! I had a few questions for you.

1. If you turn on the ignition, the gp indicator lamp comes on, and goes out when the gp's are supposedly ready. If you leave the ignition in the "on" position for say 10 seconds after the indicator lamp turns off, do they gps remain active? Do they remain active but go into the "pre-glow" period?

The reason I ask is that I have hard starting at temps between 20-40F, by performing this technique, sometimes the car will start w/less than 1second of cranking, other times it will start with 4-6 seconds of cranking (assuming same temperature both times).

I have been battling hard starting for over a year now. November 2003 my MIL came on twice in 2 weeks, first time for gp relay, 2nd for gp harness, both were fixed by the dealer. Hard starting occurred before and after this double whammy, with no difference in starting prior or after.

I have followed through this post: When I checked the resistance on gps(setting m.m. to 200ohm), I used the same ground point as in your picture. I rigorously wiped down all gp and ground surfaces with a rag to remove surface grime. Then when I measured each one, it was hard to get a stable reading. I kept my hand stable, but resistance would jump all over the place in the double digits and then settle between .7-1.1 very briefly, and then hit single digits, double digits, or read even nothing. It only read .7-1.1 for a very short period. The same thing occurred on all four plugs, which when they were within .5-1.5 ohms, all measured about .8.

I checked the harness by unplugging the coolant temp sensor, and received ~12V for all 4 plugs. I checked the voltages in the fuse box on top of the battery and all the wires measured 12V (same process as shown in your pictures).

Lastly, this is the last thing I noticed. It was ~30F this morning. The car had been sitting all night long and the first thing I tried was unplugging the coolant temp sensor. I turned on the ignition, and the gp indicator was on for roughly 20 seconds. As soon as the gp indicator went out I turned the car over and it started within 1 second.

I let it idle for about 1 min and then turned it off. About 30 mins later I went outside, stil same ambient temp, got in the car, turned on the ignition (coolant sensor is plugged back in now), gp indicator was on for less than 1 second, turned the car over once it went out, and it took about 4 seconds of cranking time!

The last thing I can think of is the coolant temp sensor is faulty. The weekend over thanksgiving I noticed on 2 consecutive days while driving, the engine started warming up to op temp, and then the needle went back down to zero, and then finally warmed up. This is the only time this has happened, has happened since.

This is long, but does anyone have any ideas?
 

gcodori

Veteran Member
Joined
Mar 16, 2005
Location
northern california (bay area)
TDI
2001 NB TDI plus CPO 2013 Passat TDI SEL Prem.
Wire harness polarity

Great How-to regarding the glow plug and harness. Regarding the two wire version, is there a specific polarity to the wires (positive/neg) or can you just clip the wires and hook them up? From the pictures, it looked you just snipped the wires.

Thanks and happy holidays.
 

Hamsterdiesel

TDIClub Enthusiast , Veteran Member & HO5G CoFound
Joined
Jul 30, 2002
Location
NH
TDI
1999 Golf IV, Black and now 2015 Reflex Silver Passat SE
Venturabass said:
The last thing I can think of is the coolant temp sensor is faulty. The weekend over thanksgiving I noticed on 2 consecutive days while driving, the engine started warming up to op temp, and then the needle went back down to zero, and then finally warmed up. This is the only time this has happened, has happened since.

This is long, but does anyone have any ideas?
This happened to me and all it was was the temp sensor. Quick easy change and all is well. It may have affected starting had it happened in the winter, but my problem was in early fall, before temps got below 40 degrees.
 

cha$e

Well-known member
Joined
Feb 9, 2001
Location
US
TDI
2010 Jetta
Wingnut - thanks very much for the prompt response, and sorry I don't seem to check this forum as frequently as you :)
The night I posted, or the next night, I went back out to the garage and sprayed parts cleaner into the 4 holes of the glowplug harness again, and cleared the codes. This caused the CEL to stay off for 3 days, but then it came back on.
During the same time period, my ex-girlfriend mentioned that she was having the same issues on her '01 or '02 Beetle, and her dad cut off the glow plug harness and soldered the wires that previously led to the harness directly to the plugs (!!) and that fixed her problem.
All this made me think "What if there is a very small gap between the contact inside the harness and the tip of the glowplug, and the parts cleaner (if it conducts electricity) is bridging the gap?"
So as an experiment, just now I tore 3 pieces of aluminum foil (a little less than 1 square inch each), wadded each into a loose ball, and inserted each one into one of the holes in the glow plug harness. I skipped the one closest to the driver's side just because it was hard to twist the harness so that that connector was upside down. Anyway, then I re-connected the harness. I had to push down considerably harder this time before it would "snap" onto each plug. I then started the engine about 5 times, and no light so far. So, hopefully I fixed it - I'll keep you posted.
 
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TDI_NC

Veteran Member
Joined
Dec 29, 2005
Location
Raleigh, NC
TDI
2001 Jetta TDI GLS 5 speed
GP wiring harness replacement and GP warm weather "mode"

Once the wires are cut on the 2 wire wiring harness how do you know which wires to connect to which on the other end? Are they marked at all? I am guessing that it does not matter?How are the two wires connected to the four glow plugs? Do all four connect to the two wires or do they connect in pairs to each wire...?Has anybody thought of disconnecting the glow plug wiring harness during the warm part of the year (in my case 8-9 months/year) and connecting it back up during winter months? Of course the glow plug tips and glow plug wiring harness terminals would have to be somehow protected from dirt, moisture, etc while disconnected. The CEL would be on for the duration too.Maybe a dummy resistive load could fool the ECU into thinking that the glow plugs are still connected?
 

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
It does not matter which 2 wires are connected. They both supply 12 volts to the plugs. 2 plugs for each wire. The ECM detects a glow plug problem if it senses a resistance difference between the 2 wires. If you have a plug with high resistance, the wire that feeds that plug will tell the ECM there is high resistance and throw the code. You can permenantly disable the sensing capabilities by stripping a 1/2" of insulation off each wire and twisting the 2 together. This will mean that both wires feed all for plugs simutaneously, and the ECM will never see a resitance variation. You will still get 12v to each plug, but it will not throw a code, so you will not be alerted to a bad plug by a CEL. But that could be a good thing for those with chronic problems that can't be cleared. You would have to manually chech your plugs every fall or winter. But if you live in the south, you can just cut the harness off all together if you desired and just twist the 2 wires together and cap them off. I don't recommend that approach, but if you never see temps below freezing, it won't hurt.
 

TDI_NC

Veteran Member
Joined
Dec 29, 2005
Location
Raleigh, NC
TDI
2001 Jetta TDI GLS 5 speed
What makes glow plugs fail?

Do GPs fail because of harsh conditions inside of an engine cylinder or is it due to the number of startup cycles (they just wear out)? It is probably a combination of the two, but I was wondering which is predominant?
 

oNNoZeLe

Well-known member
Joined
May 14, 2003
Location
Netherlands, that Europe next to germany
TDI
Golf, GLS, aut. tans, 2000, blue'ish
TDI_NC said:
Do GPs fail because of harsh conditions inside of an engine cylinder or is it due to the number of startup cycles (they just wear out)? It is probably a combination of the two, but I was wondering which is predominant?
I think it is hard to say. physics..

If 1 gp fails, the others get more juice..
then you have the heat part.. metal works and.. compare it with light bulbs.

I would think that in colder areas they would suffer more than areas like hawaii.. cause their hardly used there..

does this answer? Bosch has their gp's with a rating on their sites.. that it does minimal of xx times glows if i am correct.
 

TDI_NC

Veteran Member
Joined
Dec 29, 2005
Location
Raleigh, NC
TDI
2001 Jetta TDI GLS 5 speed
Wingnut said:
It does not matter which 2 wires are connected. They both supply 12 volts to the plugs. 2 plugs for each wire. The ECM detects a glow plug problem if it senses a resistance difference between the 2 wires. If you have a plug with high resistance, the wire that feeds that plug will tell the ECM there is high resistance and throw the code. You can permenantly disable the sensing capabilities by stripping a 1/2" of insulation off each wire and twisting the 2 together. This will mean that both wires feed all for plugs simutaneously, and the ECM will never see a resitance variation. You will still get 12v to each plug, but it will not throw a code, so you will not be alerted to a bad plug by a CEL. But that could be a good thing for those with chronic problems that can't be cleared. You would have to manually chech your plugs every fall or winter. But if you live in the south, you can just cut the harness off all together if you desired and just twist the 2 wires together and cap them off. I don't recommend that approach, but if you never see temps below freezing, it won't hurt.
Thanks Wingnut. I spliced the wiring harness wires together after stripping some insulation. The glow plugs are still powered (maybe not all of them) and no code! I'll replace the harness and the glow plugs once I have the new parts.I guess on the 4 wire harness the same thing can be done with all four wires?
 

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
TDI_NC said:
I guess on the 4 wire harness the same thing can be done with all four wires?
I don't know about that. I doubt it though. Since the ECM monitors each plug, it might get confused if the 4 wires were crossed?
 

cha$e

Well-known member
Joined
Feb 9, 2001
Location
US
TDI
2010 Jetta
Well, it's been a week, and the CEL is still off. Looks like the little balls of tinfoil are doing their job!
Also, that's a great idea about just twisting the two wires together so each wire feeds all 4 plugs, thus no difference in resistance. If the tinfoil solution fails, I'll do that.
 

shadowpuck

Veteran Member
Joined
Jun 18, 2005
Location
Mo!
TDI
'02 Black Jetta GLS
Just wanted to post up a quick thanks to everyone for creating/contributing to this thread. I recently had a code thrown for GP #1. I've also been having some hard starting issues for a few weeks - not enough to be concerned; but, enough to notice.

Using my DVM I checked each GP as the writeup describes. Found the bad one and will replace accordingly. Thanks for the great writeup!! :)
 

MOGolf

Top Post Dawg
Joined
Jun 27, 2001
Location
underneath something
TDI
2001 Golf GLS TDI Reflex silver, rough road suspension and steel skid plate, 2004 Passat Variant, Candy White, rough road suspension and geared balanced shaft module, and much, much more. 2016 LR RR HSE TD6, 2019 Jaguar I-PACE
Wingnut said:
Maybe someone with more knowledge of the wiring diagrams in the back of the Bentley can chime in as they wil probably indicate that the coolant plugs are not monitored?
In theory, they are. VW does have provision to produce fault codes 1193 (low heat) and 1194 (high heat) relay failure. I don't have a manual tranny car to test/verify.

Edit to add:

The P0380 is always related to circuit Q6 (engine glow plugs) not Q7 (coolant glow plugs). Cha$e I suspect that if your tin foil technique continues to work then the harness has had a loose connection at the GPs. If it comes back then I suspect the harness replacement job was not a good one. If this happens, let's get together and it can probably fixed better than the stealership.
 
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DonShapiro

Active member
Joined
Sep 12, 2005
Location
Ausatin TX
TDI
2005 Passat TDI, white
Thanks Wingnut

I resently got a Check Engine light, and the code was P0380. I searched TDI 101 and found Wingnuts Glow Plug 101, V2.0. The trouble shooting was quite lear and very systematic. I plan to go through it tonight on my 01 Jetta. This will save me a bundle of $$$$.
Thanks many time over,
Don Shapiro
 

JonBee

Member
Joined
Jan 24, 2006
Location
New Freedom, Pennsylvania
TDI
New Beetle 2000
The check engine light came on in my 2000 NB and when connected to the Vag-Com the DTC was P0380 (Glowplug/heater circuit fault). If my glowplugs are are acceptable after testing what is the heater circuit fault and is there any hints on where to begin?
 
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