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

sharpfork

Member
Joined
Mar 27, 2016
Location
Detroit
TDI
2001 Jetta
is 9.6v at all 4 GPs = good relay or no?

I'm still a bit confused. I have 9.6v at all 4 connections of the glowplug harness.
reading this in the initial post:
You should get around 12V at each finger of the harness...
If you do not get 12V at any time, then your relay is not completing the circuit and needs to be replaced.
I don't have 12v, I have 9.6. Do I need to replace the relay?

Thanks!

images for reference:
 

sharpfork

Member
Joined
Mar 27, 2016
Location
Detroit
TDI
2001 Jetta
Somewhere in this thread I think I posted a "magic" fix that I have used...
Thanks for this. I'm still trying to figure out what 9.6v a all 4 point in my harness means:
* good relay?
* bad relay?

If my relay is good, I might try your magic trick or just replace the harness.
 

JohnWilder

Veteran Member
Joined
Jul 13, 2013
Location
Breckenridge, TX
TDI
2003 Jetta 5 spd manual
I don't know why. I disconnected the control circuitry to the glow plugs and it trigger a CEL immediately. The other cable simply supplies the current to heat the plugs. Apparently the system doesn't know if they are working or not. It is my understanding that the circuitry checks for resistance or the balance of resistance between the plugs. I really don't know but it works on my 2003 Jetta ALH.
 

UhOh

Top Post Dawg
Joined
Dec 24, 2014
Location
PNW
TDI
2000 & 2003 Golf GLS
Thanks for this. I'm still trying to figure out what 9.6v a all 4 point in my harness means:
* good relay?
* bad relay?

If my relay is good, I might try your magic trick or just replace the harness.
My "fix" has to do with making a better connection from the harness to the glowplugs. If you're reading low voltage at the harness then you need to check/fix up-stream. Also, be sure to check promptly after switching on the ignition (and assuming temps are low enough to call for GP heating): I think you can catch the voltage w/o it being cold enough, but it takes two people to test- one to switch on the ignition and the other to check the voltage at the harness.
 

sharpfork

Member
Joined
Mar 27, 2016
Location
Detroit
TDI
2001 Jetta
If you're reading low voltage at the harness then you need to check/fix up-stream.
Does that mean the relay or the hardness itself?

Also, be sure to check promptly after switching on the ignition (and assuming temps are low enough to call for GP heating): I think you can catch the voltage w/o it being cold enough, but it takes two people to test- one to switch on the ignition and the other to check the voltage at the harness.
I pulled temp sensor, doesn't that buy me more time?
 

sharpfork

Member
Joined
Mar 27, 2016
Location
Detroit
TDI
2001 Jetta
Does that mean the relay or the hardness itself?
I pulled temp sensor, doesn't that buy me more time?

I don't have a clear view around the cause of the low voltage I'm seeing so I ordered both the harness and the relay replacement parts. I'll try replacing the relay first and see if that fixes it, if not, I'll splice in the harness. Thanks for all the help.
 

sharpfork

Member
Joined
Mar 27, 2016
Location
Detroit
TDI
2001 Jetta
I don't have a clear view around the cause of the low voltage I'm seeing so I ordered both the harness and the relay replacement parts. I'll try replacing the relay first and see if that fixes it, if not, I'll splice in the harness. Thanks for all the help.
It was the relay!
I now have new glow plugs and a new harness too but oh well. Getting up under the drivers side dash in my 2001 jetta was a bit of a pain but mostly because it was much further under the dash near the floor than I expected. once I removed the torx screws and got the panel open, swapping the parts was easy.

Thanks again, I can now get my emissions tested!
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
can I drive my vw diesel with glow plug & malfunction light on if it is cranking up fine. Can not take in to fix for a couple of days.
If it's just glow plugs illuminating the CEL, you can drive it forever. You should fix the glow plug issue.
 

Deep Fried

Active member
Joined
Jun 18, 2007
Location
Murfreesboro, TN
TDI
Golf 2001 TDI
wow, this is a long thread... I read the OP but what I am specifically looking for is a lead to the best price for a replacement harness for my 2001 TDI Golf... I know it's bad cuz when I went to remove the harness from each plug to put a probe on it to test each plug the harness material literally broke up and cracked. I first thought the piece from the long lateral body at the 90 degree turn down to the plug was "removable" since 3 out of 4 came out and left the body of the harness still on the plug and exposing the metal connection from the harness! Anyway, I need another one... where can I find the best online source (lowest price) to replace the harness. I also guess cuz it's an '01 I need the two wire harness? thanks!
 

sjurea

Active member
Joined
Aug 11, 2017
Location
Oslo
TDI
2002 Caddy (built 2001) @ 155000 km
I wonder if I bought a car with no GP-relay.
The car starts fine in summer, but has to do about two bouts of 5-second churning now in the Norwegian winter. When it starts, it skips a lot of beats for ten seconds or so, until the motor control unit raises the rpm to 1600-1700, making it go smoother. A minute or two later, it runs normally. The glow plugs are all about 0.9 Ohms. There is no voltage on the harness when glowing (measured most distal finger). There seems to be no relay in the number 10-spot; see the included picture.

 

ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
Your car probably has a solid-state controller instead of a relay... thise usually sit under the cowling beneath the windshield... next to the windshield wiper mechanism... on the left side...

Yuri
 

denismccar

Member
Joined
Jun 23, 2016
Location
Saint Louis
TDI
'05 B5.5 Passat Wagon GL TDI, '04 BEW Jetta TDI
Followed this thread to replace GP Harness. Was getting a DTC for 2 Glow Plugs intermittently. Harness was clearly bad as it was cracked and brittle in several places. GP's tested fine and fuses on battery are fine but cleaned connections anyway. Now I have DTC for all 4 Glow Plugs..... I'm going to take it apart again to ensure I made the right connections (everything else works fine so pretty confident I did cut and splice the right wires) but before I do that, looking for any other clues as to what it might be. Thanks
 

denismccar

Member
Joined
Jun 23, 2016
Location
Saint Louis
TDI
'05 B5.5 Passat Wagon GL TDI, '04 BEW Jetta TDI
Scan

4 Faults Found:

17055 - Cylinder 1 Glow Plug Circuit (Q10)
P0671 - 000 - Electrical Fault
Freeze Frame:
RPM: 882 /min
Torque: 60.0 Nm
Speed: 0.0 km/h
Load: 0.0 %
Voltage: 13.76 V
Bin. Bits: 00001100
Temperature: 23.4°C
Bin. Bits: 10110000

17056 - Cylinder 2 Glow Plug Circuit (Q11)
P0672 - 000 - Electrical Fault
Freeze Frame:
RPM: 882 /min
Torque: 60.0 Nm
Speed: 0.0 km/h
Load: 0.0 %
Voltage: 13.76 V
Bin. Bits: 00001100
Temperature: 23.4°C
Bin. Bits: 10110000

17057 - Cylinder 3 Glow Plug Circuit (Q12)
P0673 - 000 - Electrical Fault
Freeze Frame:
RPM: 882 /min
Torque: 60.0 Nm
Speed: 0.0 km/h
Load: 0.0 %
Voltage: 13.76 V
Bin. Bits: 00001100
Temperature: 23.4°C
Bin. Bits: 10110000

17058 - Cylinder 4 Glow Plug Circuit (Q13)
P0674 - 000 - Electrical Fault
Freeze Frame:
RPM: 882 /min
Torque: 60.0 Nm
Speed: 0.0 km/h
Load: 0.0 %
Voltage: 13.76 V
Bin. Bits: 00001100
Temperature: 23.4°C
Bin. Bits: 10110000
 

denismccar

Member
Joined
Jun 23, 2016
Location
Saint Louis
TDI
'05 B5.5 Passat Wagon GL TDI, '04 BEW Jetta TDI
Glow plug relay/control mechanism testing

It seems the issue is that no power is going to the glow plugs with the coolant sensor off....fuse on battery is good.... I rechecked the wiring on the new harness and it that looks good (all the cable colors match perfectly)....I checked that there is continuity from the spliced in connections to the new harness (in case new harness had a break) So, I guess the relay/control mechanism is next possible issue.... other than buying a new one, is there a way to check the current relay/control mechanism.
 

denismccar

Member
Joined
Jun 23, 2016
Location
Saint Louis
TDI
'05 B5.5 Passat Wagon GL TDI, '04 BEW Jetta TDI
Swapped out control/relay from my other tdi (same part number) and still no power to GP's. Control/relay works on other car with no codes thrown.
 

MrAsano

Member
Joined
May 23, 2017
Location
Oceanside, CA
TDI
1999 Golf 4th Gen ALH
Please help me...I have the standard glow plug error with my check engine light.
Things I have done to fix the issue.

1. Change the 109 relay under the driver side steering wheel
2. Changed my glow plugs 2 times
3. Installed a new glow plug harness (2 wire)
4. Used DeoxIT on the glow plug harness
5. Checked the fuses in the fuse relay box that sits on the battery.

What else am I missing? I have a 99 TDI that was made on October 1998. It just seems like I'm chasing my tail with this.
 

denismccar

Member
Joined
Jun 23, 2016
Location
Saint Louis
TDI
'05 B5.5 Passat Wagon GL TDI, '04 BEW Jetta TDI
Well, problem solved.....caused by my own hands lol. So, when I replaced the GP Harness instead of 'splicing' the new wires into the harness, I cut them and connected directly which obviously meant no communication was happening to the ecu. Once I went back and put it so that it was a splice in, all worked out (other than it taking forever to clear the 'Comprehensive' in Readiness. I feel such an idiot.
 

Dieselista

Active member
Joined
May 1, 2008
Location
Virginia
TDI
06 Jetta, 03 Bug, 74 TR6, 92 Ducati 907ie, 96 F250 PowerStroke
Great post thanks. It seems the link to the original post is no longer working.

Original code P0671, #1 glow plug. Worked on this today, tested resistance at each plug, all exactly 1.2 ohms. Unplugged coolant temp sensor, checked voltage at all wires for plugs, all 12.4. Initially I got no voltage at the harness, I then unplugged and plugged back in the 10 amp engine fuse at the fuse panel in the cab, and then all worked. The fuses on the battery are all tight and clean and have good voltage on both sides. Assuming this fuse may have been loose or crusty? I cleaned and applied a little dielectric grease.

I then went to AutoZone to get the code cleared, to see if I'd solved the problem. They said they aren't allowed to do this anymore, went to O'Riely and Advance, both said the same thing, not allowed to do this. They suggested going to the dealer (I can imagine how that would go, I had a new Jetta a few years ago and it was agonizing even for warranty repairs) or an auto repair shop.

Can I buy a scan tool or connection for my phone and an app that will allow me to read and clear codes? If so which one is preferred?
 

Dieselista

Active member
Joined
May 1, 2008
Location
Virginia
TDI
06 Jetta, 03 Bug, 74 TR6, 92 Ducati 907ie, 96 F250 PowerStroke
PS
I now have a new code, coolant temp sensor, from unplugging it to test the glow plugs. That's obviously not a fault, but it too needs to be cleared.
 

k_pt

Veteran Member
Joined
Oct 13, 2017
Location
pt
TDI
VW MKIV TDI
Do you guys have any solutions for glow plug wiring harness? Is there any way I can get the leads separately (like this) And make my own harness?
 

iluvmydiesels

Veteran Member
Joined
Nov 21, 2015
Location
phila area
TDI
AHU
a little help, pls, wingnut,guys.
have a mk3. its my coolant glow plugs. havent worked for sometime. today i went to test them. its 40dg F out. i turn on the ignition, no voltage at any of the 3coolant GPs. turn the car on, its dead cold, or been off for more than an hour. again i can get no voltage reading here(any of the 3). gotta try to look up in the manual fuses and relay(s) to check. i have 3 of those GPs on order, rather expensive. yet not getting any volts at GPs would be the first thing to solve. either that or hook-up my vag-com to be able to activate.
i dont think there is even a notation of them in my coolant section of my manual.
was looking at some of this thread, man its sooo long, nice on that! just a little help, pls, may get me going. thks.
or even that kiss-of-death wire harness connection right by it, the head.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Don't know if there is much on the coolant GPs in this monster thread, but most of us just let it go, they seem to do very little. Perhaps it's more of a problem with the AHU.
VW TDI Search Engine
 

iluvmydiesels

Veteran Member
Joined
Nov 21, 2015
Location
phila area
TDI
AHU
thanks for the link. nice one.
the vwdiesel.net post, link showed me a lot.
no luck, yet. so i found the fuse box. was wondering which was which. checked both, the one on the firewall, its said this is the coolant glow plug box. cleaned both. (the other is by the coolant jug. it has a 20a fuse in it, and the other fuse opening looks like a blank??). (the firewall box>)so this one, i have one wire coming into the fuse, and the fuse secure. i have 14+ volts here. (and the same voltage reading on the other side connector of fuse, so fuse is good) a lower big wire. no current here. a smaller lower wire, slip connected on, nothing here. and the 3 prong connector in the middle(bottom).
so to try to trick the system i unhooked a few connectors. i think the coolant connection in the middle of the hose going to the top of the radiator is for A/C operation, the coolant main sensor i have is right by the head, the main front flange, unhooked this, no help there, im not sure of all this sensors operation. its 4 prong. im not 100% sure where the intake ambient air temp sensor it. i unhooked the one coming out of the air (filter)box. i believe its a maff or mapp sensor.
so looks like i have to have a shop take a look at it. its gotta be the reading going to the 3 prong bottom fuse box connector.
 
Top