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

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
TDI Allen just did a great writeup with pictures on how to change the 4 wire harness. So those of you who want to go that route will have a good idea of what it takes. It is quite involved, so I still suggest trying to treat your harness before going to this step. But if you decide to do it, TDI Allen has made the job much easier for you. Here is the link
 

DVDVW

Veteran Member
Joined
Oct 11, 2003
Location
Quebec City / Quebec / Canada
TDI
2003 Honda Element Etheral Blue Pearl, Y package, AWD, AND NEED A TDI ENGINE SO BAD
My car :

2001 Golf GL TDI 2 doors

My fault code :

16-764 - Glow Plug / Heater ( Q6 ) Circuit Malfunction

P0380-35-10 intermitent

My question.

My car ( 2001 or older ) will only get the P0380 code, regardless of the glow plug ( coolant or engine ) or harness is in cause? So I need to test all 7 glow plugs and harness to found where is the problem?

Thank you all.
 

Bill_Blazek

Veteran Member
Joined
Sep 28, 2004
Location
Littleton, Co
TDI
2002 Golf GLS TDI, 5 spd, Navy Blue
Wingnut,

Thanks for all the great write-ups like this one!

A couple more detailed questions on GP operation.
Following this write-up I testing my GPs and harness
and found a bad GP. It had infinite resistance.
It went over a weekend before I could get the
new GP and replace it. It may have even been out sometime before that.
Once I did get it replaced I had noticeably more
acceleration, especially from a dead stop up a hill.
I also noticed low gas mileage on the previous tank.
However I have never had trouble starting the engine at all.
Fires right up every time.

My questions:
Do the GPs stay on all the time helping the compression ignition
or do they only stay on for the ~20 seconds during starting?
Was I running on 3 cylinders while the plug was not working?
The engine was running awfully smooth for only 3 cylinders.
I had a hard time telling the was any problem at all.
I was assuming that GPs only operated when starting the engine
and that once it was running they shut off.
Do you or anyone else know more about the details of GP operation
during and after starting?

Thanks again. The info here has been tremendous!

Bill
 

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
Glow plugs are used primarily for cold starting. They activate when the coolant temp is below 9*C (45*F). This is knows as pre-glow. They will also stay on for a period of time while the engine warms up. It is just to assist with the combustion. This is sometimes referrd to as afterglow. They turn off as soon as the engine RPM goes over 2500 RPM. So on a cold morning, while driving away after a cold start, you can hear the relay clicking everytime you go over & under 2500 RPM. This is the glow plugs being turned off & on. This stops as soon as the coolant temp rises. This feature is mostly for emissions to help ignite the fuel a little more completely when cold.

So to answer your question, your percieved power probably has nothing to do with the replacement of the glow plug. Unless you noticed the extra power right after a cold start and you experienced it before the coolant warmed up? But glow plugs have nothing to do with the running of a diesel. They are just used to aid in starting. Once started, diesel engines run on compression, unlike gassers who need the spark plug for ignition.
 

Bill_Blazek

Veteran Member
Joined
Sep 28, 2004
Location
Littleton, Co
TDI
2002 Golf GLS TDI, 5 spd, Navy Blue
Wingnut,

Thanks much!
That's what I thought.

The engine was luke warm when I changed the plug and
thought I noticed more pickup immediately afterwards.
This AM when it was cool, in a partially heated garage,
it seemed to be better too. But also after it had
completely warmed up. Could have just been my perceptions!

I did notice that it did run smoother in the ~30 seconds
immediately after cold/cool starting this AM.
It wasn't very bad before but noticable and its
notically better the AM.
Will definitely keep an ear on it.

I also just did the ventecomy near the end of the last tank
so I was able to put in 14.3 gals and the low fuel light had
not even come on yet so that threw off the MPG calculation.

Thanks again for all the great info.

Bill
 

respond2us

Veteran Member
Joined
Nov 5, 2004
Location
Tulsa, Oklahoma
TDI
Jetta, 99.5, Custom - Funky Green. 99 NB TDI, 06 Jetta TDI
Great thread, everyone. Very helpful. Just wanted to add my .02, though. I was going to replace only 1 or 2 plugs, since VW dealer wanted like $40 per, but I called O'Rielly Auto Parts and they had Champion plugs for $11 each. Just wanted to throw that out there... I went ahead and replaced them all since they were so cheap. <font color="green"> </font> <font color="green"> </font>
 

Bill_Blazek

Veteran Member
Joined
Sep 28, 2004
Location
Littleton, Co
TDI
2002 Golf GLS TDI, 5 spd, Navy Blue
Just out of curiosity, does anyone else, like the guys up in Canada,
have any serious, real world, long cold winter experience,
with other brands of GPs, beside Bosch and Beru, like Champion?
How reliable are they and how long do they last?
Are the Bosch and Beru really worth the extra $$$???
I haven't seen any other brands mentioned much here.

Respond2us,
Let us know how they work this winter for you in Ok!
How cold does it get there in winter?
 

celry

Well-known member
Joined
Jul 6, 2004
Location
Washington DC
TDI
2001 Jetta auto; 2011 JSW dsg
hello everyone

first, thank you for all of the glow plug information and advice! this site in general is a huge breath of fresh air for people like me who are 1)really frustrated with the local vw dealer and 2)mechanically interested in their car.

my 2001 automatic jetta has the P0380 fault code, so i've started wingnut's diagnostic procedure.
the plug resistance reads ok, so on to the relay/harness step. BUT despite wingnut's clearly noted photo, i haven't been able to locate the coolant temp sensor or even the coolant glow plugs.
would anyone help me identify exactly where these parts are?

thanks!
 

Wingnut

Top Post Dawg
Joined
Oct 10, 2002
Location
Toronto & Whitby
TDI
Silver 2003 Jetta Wagon
Since you have an automatic, you do not have any coolant glow plugs. So in your case, follow the upper radiator hose from the radiator to the block. It attaches to a housing on the drivers side of the head. The coolant temp sensor is located on the back side of this housing facing towards the firewall.
 

Bill_Blazek

Veteran Member
Joined
Sep 28, 2004
Location
Littleton, Co
TDI
2002 Golf GLS TDI, 5 spd, Navy Blue
Well that explains why I haven't been able to find mine either!!
I have looked for them several times and not found them!
Thanks!
 

egh2001

Active member
Joined
Sep 3, 2003
Location
West Virginia
TDI
2009 Jetta Sedan
Thanks for the post, you helped solve my problem. I found that the #2 cyl glow plug was bad not the #3. I guess the computer can't tell the difference. Thanks again. and your post was great.
 

savis01

Member
Joined
Jun 25, 2004
Location
IL
TDI
2000 beetle 1.9 tdi yellow
Wow, I have fixed my car I ended up changing my glow plugs(re-checked the ohm's) and auto zone cleared my fault for free everything is working. Next step timing belt.

Thanks
Steven Saville
 

DVDVW

Veteran Member
Joined
Oct 11, 2003
Location
Quebec City / Quebec / Canada
TDI
2003 Honda Element Etheral Blue Pearl, Y package, AWD, AND NEED A TDI ENGINE SO BAD
When you will check your glow plugs, put dielectric grease on them. Since I made that, no more starting problem. The car start fine at -25°C, like last year!
 

Paul_L_Fisher

Veteran Member
Joined
Aug 28, 2003
Location
San Tan Valley, AZ
TDI
None
OK. I have P0380 as my code and a flashing GP light and I have a 2000 Golf. I have tested all 7 GP's and they all read 0.5 ohm. I have read the voltage at the 4 engine GP after diconnecting the ECT and they all read what the battery says. When I read the voltage at the coolant GP's, I cannot get a reading. What needs to be done to turn them on? The Bentley wiring diagram shows that there should be 2 relays #53 (J359
Pictures from Bentley CD

and J360

) that control the coolant GP's. Looking, I only have one #53 and a #100
Picture from my car


I am willing to replace the GP harness, however am concerned why my coolant GP's don't show voltage.
 

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
The P380 is related to the engine GPs, not the coolant GPs. Stop worrying about them. If the engine GPs are fine, the next step would be replacement of the harness because of oxidation at the contacts. Or just clear the code and see if it comes back.

The flashing GP light is not related to the GPs. Check the operation of your brake lights. If you have burned out bulbs, replace them. If the bulbs are good but the light don't operate, then the switch is probably bad. (Covered in numerous threads).

I suggest meeting up with someone with VAG-COM to get a proper diagnosis.

Those coolant GPs are activated by the ECM based on the coolant temp during the initial warm up. Relay 100 is used to power 2 of the 3 GPs and the 53 is used to power 1 of GPs.
 

Paul_L_Fisher

Veteran Member
Joined
Aug 28, 2003
Location
San Tan Valley, AZ
TDI
None
I guess that is what I wanted to make sure of (no monitoring of coolant GP's). I'll put everything back together with some dielectric grease, get the code cleared and see it it goes away.

The brake lights go on every time I have checked them. Is there 2 brake switches? On my Taurus, there was one that did the lights and one that did the cruise. Is the Golf the same?

As for the relay mixup, the Bentley cleary states on the wiring diagram that there are 2 #53's. Is it a SNAFU from Bentley or is my car 'special'?
 

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
Brake light switch has both of the switches you mention in one package. Jettas and NBs got recalled for the switch going bad, but not Golfs.

Your car's got the higher current capable relay. This relay 100 is also used as the 'load reduction' relay behind the instrument panel. The Bentley is not 100% accurate, and parts are 'subject to change without notice'.
 

cwaglytdi

Member
Joined
Nov 10, 2004
Location
Calgary Canada
TDI
2001 VW Jetta TDI
Hi Everyone,

Merry Belated Christmas and a Happy New year!!!

Question: I have a 2001 Jetti TDI and it has about 103,000 km's on it. I just had to replace a glowplug as it "quit" on me. How often should glowplugs last and/or when should they be changed?

Thanks
 

doc_m

Top Post Dawg
Joined
Dec 2, 2002
Location
somwhere
TDI
None
wingnut thanks for your awesome posts, in the how to's link I put a pdf if it's easier for people to print it off, next is the starter cleaning as mine is sounding kinda funny but just noticed a little cleaning and i will be happily on my way
 

Paul_L_Fisher

Veteran Member
Joined
Aug 28, 2003
Location
San Tan Valley, AZ
TDI
None
So it is possible that one 'side' of the switch is bad and the side that actually does the lights is still working. Should I order the Jetta recall switch or should I just go to VW and get whatever they say?
 

Noplugs

Member
Joined
Sep 13, 2004
Location
Florida
TDI
Beetle 2000 Drk Blue
Glow plug are not a time change item. Their life span depends on their use. If you live in the south where they come on for short warm-up period, they should last years, I lived in Florida for the first 4 years of my N/B. I replace them on its 3rd year and used the original harness. Now that I live up north I exspect that to be reduced...How much you ask. Well I have no clue but if I was to guess I think it would be reduced by 25-50%. So my advice is dont worry about them unless your losing sleep.
 

Goldie

Well-known member
Joined
May 8, 2004
Location
Ferrisburg, Vermont
TDI
1996 Passat TDI
Thanks for all of the great information on this thread. I am having a bit of problem that I'm hoping someone can help me with. I am a neophyte with electronics so bare with me.

I don't think that my 1996 Passat is starting with the help of glowplugs. I have to crank for about 20 seconds which is accompanied by lots of white smoke. I drive the thing before bed - it seems to help in the morning. It's been cold here, luckily for the starter.

I am getting a check engine light sometimes, but I haven't been able to download the codes yet. It's happening inadvertently. Another way to say that is that I can't figure out what is causing it. Sometimes it happens right after the glow plugs cycle, sometimes after I start driving and get it into 2nd. Sometimes I can turn off the car and start it again and the light won't come on.

I'm assuming that the light has something to do with the glowplugs.

I got a multimeter and I've tried it out but I don't think I am using it correctly or I got the wrong meter or the plugs are shot. I set the function switch on the meter to measure resistance. There are settings for 2, 20, 200, and 200 ohms. I tried it at all 4. When the meter is on and not connected to anything, the readout says "1." I assume that is infinity? When I touch the + to the - leads the readout drops to ".000"

But when I brought the meter out to the car and touched the + to a plug and the - to a selection of possible grounds, the readout didn't change ("1.") Am I doing something wrong? Or are all of my plugs shot? They look to be in good condition - no oxidation.

Thanks!

Jared
 

pismosisks

Member
Joined
Feb 28, 2005
TDI
New Beetle, 2002, black
Many many thanks Wingnut!

Our check engine light popped on yesterday, and the ODB scanner I borrowed from the local parts store gave me a code for a failed glow plug #2. I did a search on this site and found your post. Popped the engine cover off for the first time on my own (all previous service by dealer), and dived in. With your instructions, I was able to verify the bad plug in about two minutes. Its resistance was off the scale, but the other three were 0.8 - 0.9 ohms, right in the range you said. The local parts store has one in stock, so I hope to pick it up on the way home from work and swap it out tomorrow night.

Again, many thanks for such detailed and accurate instructions.
 

Bill_Blazek

Veteran Member
Joined
Sep 28, 2004
Location
Littleton, Co
TDI
2002 Golf GLS TDI, 5 spd, Navy Blue
Jared,

If your car was generating a glow plug DTC, diagnostic trouble code,
usually P0380 or similar if its for a specific plug for the newer models,
the CEL would come on shortly after starting - within ~30seconds - 1 minute,
and would stay on all the time as long as it was running.
Once it generates the DTC,
this will happen everytime you start the car until you
fix the problem and use an OBDII scan tool to clear it.

So if your CEL is not staying on all the time, its not glow plugs.
Use an OBDII scan tool or VAG-COM to findout if you have any DTCs.
Many auto parts stores are now letting people use one to read and clear the DTCs.
Or better yet, find someone with VAG-COM to get the codes.

It sounds like your testing the plugs correctly.
I use the lowest setting you have.
Mine generates a steady beep on this lowest setting when it measures a current.
If you use too high of a setting,
the resistance may be so low it does not register.
When you test it, touch the + to the tip of the plug and
the - to the block somewhere close to the plug.

Also test the harness itself as described in the original posting.

Good luck
 

Goldie

Well-known member
Joined
May 8, 2004
Location
Ferrisburg, Vermont
TDI
1996 Passat TDI
Thanks for your reply Bill.

I changed the plugs and she seems to be starting fine. The CEL is still coming on as you described, seconds after cycling the plugs/starting. It stays on all of the time. I gave up on checking the resistance, but now that things are working alright, I'll get back out there just for the lesson.

Best,

Jared
 
Top