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

mrrossi

New member
Joined
Sep 15, 2014
Location
Nottingham, UK
TDI
Seat Leon 1.9TDi FR (2004)
Hi all

I had the code for the glow plugs for my 2004 Seat Leon 1.9TDi FR and followed this guide to test the resistance of the glow plugs - all looks good.

The harness though literally started to crumble in my hands and looks likely to be the culprit... I wanted to do the next test, but wasn't sure where the coolant temp sensor is on my car? Here's a pic of the engine bay... I can see what looks to be the coolant glow plugs on the right hand side (similar to the pic of the Passat on this guide) but couldn't see a sensor underneath... should I be looking elsewhere?



Thanks
Ross
 

jettabobetta

Member
Joined
Jul 1, 2014
Location
Indiana
TDI
jetta
I put a new temp sensor on but it still does it. I disconnected the temp sensor so the plug will stay on and is has cured my symptoms.. So would u think it's a relay?
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
I put a new temp sensor on but it still does it. I disconnected the temp sensor so the plug will stay on and is has cured my symptoms.. So would u think it's a relay?
What temperature is the car when you try to start it?

If it's above 40, it's doing what it's suppose to do.

If it's under 35, it's something to investigate.
 

JB05

Top Post Dawg
Joined
Oct 20, 2005
Location
Il.USA
TDI
Golf,2005,anthracite blue
The glow plug light is not a pilot light. The glow plugs activate year round; both pre glow and after glow. In my BEW the GP's will still get voltage 15 or more seconds after the light goes out.
No sensor for the coolant GP's. They are controlled by two relays that are grounded through the ECU. Not sure what temperatures they are activated. DanG has a thread that goes into some detail for the coolant GP's.
http://forums.tdiclub.com/showthread.php?t=269731
 
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Briggz

Active member
Joined
Oct 28, 2012
Location
NC
TDI
2003 Jetta Wagon
just changed my GP using the the tutorial, thanks. It was a breeze
 

Vwscream

Veteran Member
Joined
Jan 19, 2014
Location
Chicago
TDI
90 Corrado 1Z, 97 1Z Passat, 85 Golf NA
Feels as there is more ALH diag info in the posting and less about B4's.

Glow plugs not functioning during pre-glow and after-glow on B4 early 1996 TDI swapped into Corrado. Not 100% sure if after-glow is not functioning. Currently ambient temps are high in the 50's and drop to 30's. I believe the problem was going on before I did the swap and installed new injectors. With new injectors I get much more white smoke during cold starts. Engine misfires on number of cylinders but is able to start. Smoke is way to much and lasts to long. Side note it also smokes blue after engine starts to run smoother. Have lit of oil consumption from it.

Getting back to GP issue. Have new glow plugs, harness and when running output test in vagcom I do pull correct 48amps or so with 11.5v at harness. When koeo I do not get GP at all. When I unplug temp sensor I get GP. What is causing the GP not to kick on at all? Last week when driving I felt the GP relay with my hand and it does kick on at low rpms and shuts off after 2500rpms. Also normal to see was headlamps get dim as GP relay energized do to current draw. So it would seem as my glow plugs are not going through pre-glow function. Not sure if that was not the coolant flange glow plugs.

Right now I have the car in my garage where it's maybe 55F and there should be few sec of glow plug activation but I'm seeing none. I swapped my old ECU to eliminate the one with stage 3 tune with no change. Have plugged in new temp sensor with no change.

Do to the ambient temps being over 40F the next few days and I would like to get this diag moving along I may try to trick the coolant sensor by cooling it down under 40F using keyboard cleaner or gum remover and check what vagcom reads to check if I get glow plug pre-glow.

Even if I do get GP kick on at low temp I find the large issue of having a lot of white smoke any time the car is started even at 90F ambient.

Mechanically I have 500psi +/- 20. During compression check spec 450psi. That can gauge difference and car on build up but otherwise the engine has ample compression when testing cold.

A lot to read but thank you for any input.

Update: After doing testing 9c/48F coolant temp is the window for pre-glow to occur. When engine is started after-glow will occur till operating temp and rpms under 2,500.
 
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jettabobetta

Member
Joined
Jul 1, 2014
Location
Indiana
TDI
jetta
I'm still having problems with gp not coming on. White smoke and shaky cold start. I replaced the coolant sensor, no fix... If i leave it unplugged the gp light comes on and stays on... I'm curious where the gp relay is located as well...
 

flan

Veteran Member
Joined
Jul 3, 2014
Location
On my couch
TDI
04 tdi jetta
My PD glow plug light came on for about 3 sec this am and shut off so I went to start and it ran but pumped out blue smoke and stumbled for about 10 sec. It was 30deg out. Glow plug issue I presume? No cel on.
 
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jettabobetta

Member
Joined
Jul 1, 2014
Location
Indiana
TDI
jetta
My temp sensor starting coming on at first startup, but not every time. I've replaced this a couple mos. ago. Thoughts.? Maybe the relay or should i take it to the stealership?
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
Springfield, VA
TDI
‘18 Tesla Model 3D+, ‘14 Cadillac ELR, ‘13 Fiat 500e
I am sticking this thread for the winter season. Check your glow plugs. :)
 

highender

Veteran Member
Joined
Oct 8, 2006
Location
Northern California
TDI
2012 Jetta TDI
Good idea Veedub.


And for all you who have not checked your glowplug system, do not forget to spray all four connectors with DeOxit or other anti oxidizer spray. This frequently fixes any check glow plug CEL /MIL lights.

IT worked for me . Now I sprayed it on all other
 

jettabobetta

Member
Joined
Jul 1, 2014
Location
Indiana
TDI
jetta
My temp sensor starting coming on at first startup, but not every time. I've replaced this a couple mos. ago. Thoughts.? Maybe the relay or should i take it to the stealership?
I took it to the stealership to figure this out since it is getting cold. they tell me its b/c the contacts on the temp sensor are corroded?? and that it would have to be re-pinned. has anyone heard of this one before? I took it apart and sprayed it with contact cleaner and replaced the sensor AGAIN with a VW unit. still doesn't work. I don't trust this dealership and really don't want to pay the $300 for them to "re-pin" the connector unless I'm certain it will fix it.
 

Dieselknight

Member
Joined
Nov 7, 2014
Location
East Bay, CA
TDI
2000 Jetta TDI
I took it to the stealership to figure this out since it is getting cold. they tell me its b/c the contacts on the temp sensor are corroded?? and that it would have to be re-pinned. has anyone heard of this one before? I took it apart and sprayed it with contact cleaner and replaced the sensor AGAIN with a VW unit. still doesn't work. I don't trust this dealership and really don't want to pay the $300 for them to "re-pin" the connector unless I'm certain it will fix it.

I would spray all electrical contacts connectors that go to and from the temperature sensor.

I had a glowplug P380 code last month. I took apart all connections and sprayed all connections twice with DeOxit. Then reconnected them. No more codes thrown.

Not to say that will solve your problem, but many times the corrosion at the connectors causes increased resistance , thus throwing a code.
 

rmidgett

Well-known member
Joined
Feb 10, 2012
Location
Nashville
TDI
2001 Jetta GLS
Threading Glow Plug Studs

Thanks for this! It's exactly what I was thinking of doing in lieu of buying a new $100 harness.:D


After removing the battery and airfilter:




pull the cover off the plastic cable conduit...you'll see a bunch of loomed wires and big plastic glow plug harness connector with two red/white stripe heavy duty wires:






For your purposes ignore the red wires in the above picture... that's my harness delete. I've threaded the tops of my glowplugs for 8/32 Kepps nuts and run individual spade lug terminals... another option for those so inclined:



 

rmidgett

Well-known member
Joined
Feb 10, 2012
Location
Nashville
TDI
2001 Jetta GLS
Glow Plug Stud Threading

I'd like to know if you encountered any difficulty threading the glow plug studs, such as snapping off the stud in the process. The stud appears to have a high brass content, based on your photos.
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Yup, they have a high brass content, since they are optimized for electrical connection, so I found it helpful to grab the base with some needle-nose vice grips during threading. If you look closely at the detail picture you can just make out the teeth marks. :)
 

ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
Since my coolant-glow-plug connectors just disintegrated, I may do the same thing... I would, however, put some insulation over the contacts... (plasti-dip ??? I've had some sitting around forever... waiting for an application...)

Yuri
 

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
Yup, when I do it on my other Jetta I'll probably snag four old spark plug boots. The odds of a short are very very low, particularly since those leads are only energized for a short period of time, but....

What's a spark plug, right?!?!? :):)
 

craimondi

Member
Joined
Nov 20, 2014
Location
Chicago
TDI
2004
Followed your threads and had done some modifications to remove the the Glow Plug Relay (nasty beast to remove). I still have to replace the the harness but knock on wood, no check engine light. What was interesting on my Jetta, (before relay change) the voltage when first tested displayed 3v on some plugs and 8v on the others but when I did a recheck on the ones that were giving me 8v, I noticed only 3v again. After replacing the relay, I now get 8v steady. Your pictures were great asset to me. Love it. thank you.
 

JohnWilder

Veteran Member
Joined
Jul 13, 2013
Location
Breckenridge, TX
TDI
2003 Jetta 5 spd manual
Hello guys. Excellent write up. I had a code for #2 in my 2003 Jetta. I purchased the glow plug (it was in stock) for $22.40 plus tax. I changed it out in 30 minutes. I'd never done it before. It is not difficult.
I've a question. I live in Texas. It just never gets cold here and a glow plug is not necessary to start a diesel here. I would like to disconnect the glow plug harness. That will eliminate anymore glow plugs burning out. Is this possible and not generate CEL lights?
 

shak911

Veteran Member
Joined
Nov 2, 2010
Location
toronto
TDI
2004 Jetta TDI-372000KM
Hello guys. Excellent write up. I had a code for #2 in my 2003 Jetta. I purchased the glow plug (it was in stock) for $22.40 plus tax. I changed it out in 30 minutes. I'd never done it before. It is not difficult.
I've a question. I live in Texas. It just never gets cold here and a glow plug is not necessary to start a diesel here. I would like to disconnect the glow plug harness. That will eliminate anymore glow plugs burning out. Is this possible and not generate CEL lights?
On my 04 BEW, I noticed the glow plugs do not necessarily turn on every time you turn on the ignition, the in dash icon comes on just as bulb test, and turns off in 1 sec or so, I noticed this since I installed in car 4 LEDs to monitor the voltage status on the 4 plugs...

I am also in the process of rewiring the ECT circuit, with a switch, where I have the option to select the ECT current value to relay to the ECU, or switch-on a set value resistor in place of the ECT, to trick the ECU it is cold cold, I am starting with 5k resistor, I may have to up it a little....

I suppose you can do the same, but instead the resistor value will have to be around 2k, that will trick the ecu it is around 70-75F.

Frankly, I would not bother if I lived in Texas...but I don't....



One other thing I noticed, when LEDs do come on, they are flashing rather than steady, flash rate is 10-15/second,(pulsating DC) I am guessing this is so to extend the life of the plug....is this true?

Can anyone confirm this, one way or another...sorry I did not read all 100 pages of this thread.
 
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