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

Most likely your # 2 glow plug is on Cylinder # 3... when facing the engine, it's the third from the left... (the # 3 cylinder has the longer fuel injector with the sensor...)

There _are_ exceptions to this reverse-numbering routine, so it's not a given that this is the case with your particular car...

Also, it's possible that the problem is caused by corrosion inside the harness rather than a defective glow plug... Since you checked the resistance, this is a good possibility...

After all this, you'll need to get the code cleared by either Vag-Com or a generic scanner...

Yuri.

Ok I Here is what I have. I just bought a 2001 jetta with 81000 miles on it. It has all of the service records and was serviced at the dealership up untill jan of this year. The check engine light came on and it turned out to be the glow plug code. I read this thread and here is where I am at.

Tested the glow plugs.(all appear to be brand new) and they all tested out at 1.5 ohms in the head.

I then tested the relay even though I have a service record saying it was replaced 10000 miles ago. Every plug end tested out at 12volts. The fuse area looked like brand new.

I then inspected the harness and saw that it has been recently replaced. There is no corrosion or anything that appears to be wrong with it but I still took some sand paper and cleaned inside of it and then took took a wire brush to the top of the glow plug. They used crimps to attach it but they appeared to be a good connection. I only had a small amount of di electric grease to put on the top of the glow plugs so I did. I took it to autozone and had the code cleared out.(also there was now a 1256 code but I figured out that was because I had disconnected the temp sensor to test the relay).I drove it last night and the code stayed out I drove it to work this morning and no light. At lunch today the light comes on again.

I decided to inspect all of the wiring and connections before I went any farther. I tested the continuity of the wiring harness on the glow plug side of the butt splice they put in and both wires tested at .8 ohms. I tested it on the other side of the splice and both wires tested at 1.1 ohms. I then did a voltage drop test on the splice they put in and I had 11.5 on all 4 sides of the splice so I assumed the splice was good. I then went to the connector that is in the black chute that houses all of the wiring and found the plug that has the wires for the glow plug harness and took it apart. It looked fine. Because I didn't want to wait to order the deoxit I bought a product today at lowes. It claims to lubricate, protect, clean, and encourage electrical connection. I sprayed the plug just to be safe.I decided to test the voltage at the plug and I had 12.5 which was surprising since that means I am losing 1 volt in the harness. Is this normal? After cleaning everything and spraying it I tested the continuity of the harness again at the splice and this time all four side's tested out at 1.2 I don't understand that either. Shouldn't cleaning everything have lowered the overall resistence?

Next I took out the glow plugs and tested them out of the head and they all tested out at 1.3 out of the head. I cleaned the threads and then I sprayed on the product I bought today. I installed them back in the head. I used the same product inside the boot of the wiring harness.I put everything back together with it all cleaned and sprayed. I took the car and had the codes removed at auto zone. so far so good. If the code comes back tomorrow I am going to cut the butt splice and solder the connection even though it tested out fine. The only problem there is that if I do that I have to actually splice a wire in because they didn't leave enough and now I am introducing 2 new connections in.


I have come to a few conclusions. All of the new parts seem to indicate that this car has been having this issue for a while and the dealership couldn't fix it. I am a little nervous now beause all of the parts in the system are new and tested out well and I hope this isn't an electrical Gremlin that never gets sorted out because the rest of the car is ridiculously clean and well taken care of. Also I am running out of things to try other then replacing the crimp connection's. I really don't see any need to replace the whole harness sine it seems like it was just replaced and looked like new inside. Does anyone else have any ideas on what to try next?

Clean the grounds. Probably won't help, b ut clean the grounds.

Recalibrate your Ohm meter. New plugs should be .6-.8 with good contacts.

Do you have a VagCom? Not important except for the ease of clearing codes.

Some have hit this situation and connected the two wires together so both will read the same all the time. In South Bend, you might not want to do this since it would eliminate the ability to diagnose bad gps in the future. However, if the issue won't go away.....

check the connector to the ecu. Make sure it's shiny-bright on both sides.

KM. I'm still a bit suspicious/leery about the robustness of the GP terminal boot springy connectors.
I hope that yours are still all feeling tight; Larry

Well it hasn't come back on yet but if I had to question any of the parts it would be the harness connections to the GP. I don't like it either and I am surprised that some one hasn't made there own yet considering I called the dealer and they said it would be 50 dollars for one. I think if it comes back I am going to build my own harness and see if that helps but with any luck I won't have this issue for a while but we will see. Wouldn't my gp having a higher resistence be better because they would heat up hotter and faster?

Remember Ohm's law? You want as many amps as possible through those gps.

Solder on GP ends

Having lived with this issue for quite a while ... and my GPs are still good, I just know
that it's the harness spring contacts, instead of buying a new harness I want to try and
fatten up those GP tips. I'm going to use ordinary solder, on the GP tips. I know it's
not recommended in a high-current application, but I'm going to do it anyway. Has
anyone else tried that?

l_c said:

Having lived with this issue for quite a while ... and my GPs are still good, I just know
that it's the harness spring contacts, instead of buying a new harness I want to try and
fatten up those GP tips. I'm going to use ordinary solder, on the GP tips. I know it's
not recommended in a high-current application, but I'm going to do it anyway. Has
anyone else tried that?

Click to expand...

I'd be more inclined to try a mild squeeze on the connector with a Vice Grip.

I had the old glow plug code again today. A good harness cleaning seems to have fixed it. I suppose cleaning the harness every 2 years ain't too bad

I've been thinking about this recently. I remember seeing a picture where the GP harness had been taken apart and it showed the corroded spots between the inner sleeve and the outer sleeve. Since there is no way to get anything in there to physically remove it, I was thinking of turning the harness upside down and giving one hole at a time a good shot of Deoxit, then using an old GP to go in there and try to move the two pieces against each other. This would work the Deoxit into places that it wouldn't normally get and it would give some physical action of scraping the corrosion off.

Just me thinks for the night. Time to go find some beer.

Good idea whitedog:



Cleaning the surface between the liner & the crimp is imposible with a brush or sandpaper. Only the Deoxit will work. But pushing an old GP in & out several times to work the joint is a good idea.

wanders said:

I'd be more inclined to try a mild squeeze on the connector with a Vice Grip.

I had the old glow plug code again today. A good harness cleaning seems to have fixed it. I suppose cleaning the harness every 2 years ain't too bad

Click to expand...

Just get a new harness, for about 50 bucks, and be done with it. How much time and energy do we have to spend on this common problem. I have tried all the different remendies, it always came back. New harness, problem solved.

Wingnut said:

But pushing an old ?? in & out several times to work the joint is a good idea.

Click to expand...

Good idea Wingnut.

So the two pieces can move in relation to each other? This is good to know since a friend of mine had a #3 GP code and it cleared, so I'm sure it is a connection problem.

mtbr297: Some times it works, sometimes it doesn't, apparently. It just depends on how bad it's corroded.

mtbr297 said:

Just get a new harness, for about 50 bucks, and be done with it. How much time and energy do we have to spend on this common problem. I have tried all the different remendies, it always came back. New harness, problem solved.

Click to expand...

Time & energy is subjective. Most people on this board are enthusiast who like to get involved with their cars. If time was an issue, then most wouldn't be members here and they would simply take the car to a dealer and pay the big $$$ to get it fixed. I don't want to paint everyone on this forum with the same brush, but we seem to be frugal folks. Or at least people who like to tinker. This is a DIY community for the most part.

As for time, it takes more time & effort to cut out & splice in a new harness than it does to pop it of, spray it with some deoxit, give it a squeeze and pop it back on. Especialy with the 4 wire harnesses. They can be upwards of 1 hour if you chase the wires all the way up the loom to the plug.

I hear where your coming from and beleive me, I have convinced customers to replace parts before that could have possibly been fixed, but the time to fix it was more than the time & cost to replace it. That is not the case with the harness. IMO, treating it will cure the problem in 95% of the cases. Im my 4 years of fixing TDI's, I have only ever replaced 3 harneses. One was my own before I found out about Deoxit and the other 2 the customers already had the part with them when they came. All the other occurences of the GP CEL (that were not plug related) were fixed with a shot of deoxit in the harness.

Now that is just my experiences (less than 100 cars). So others may have different experiences and higher rates of failure with the harnesses. But to me, it is common sense to try a 20 minute fix with a $10 can of Deoxit than an hour repair with a $50 harness. If the deoxit doesn't work, it only cost you $10 and a half an hour of your time. And even then, you have the deoxit as a preventative measure to treat the new harness when you install it, so it wasn't a wasted $10.

Now I will admit, there are people whos time is more valuable than money. But those are not the people I wrote this article for. I just don't beleive in throwing parts at a problem till its fixed. I like the methodical approach and trying to diagnose the source of the problem and fixing it starting with the simplest & cheapest solution first. If it doesn't work, well, at least is was cheap and easy, then you go to the next step.

Re: Ways to fix GP harness issue

Forgot to mention -- I have 120K miles on the original (2002) harness now.
I've squirted DeOxIt D5 on a few occasions (w/boot openings pointed upward),
and have tried sticking metal tools in there to scrape. But I forgot to try using
an old GP, I will try that. I have squeezed the boots with various large pliers,
a few times -- it's tricky to figure out exactly where to place the jaws, and
personally I don't know whether my squeezing has done anything.

I would definitely have just replaced the GP harness by now, if it didn't involve
unravelling the wire loom and separating so much cabling ... my electrical work
is not very tidy, but I may try this (installing a new harness) when I get more
time and am more fed up with the situation. I think first I'm going to flow
some solder onto those tips, to forestall the issue. Larry

The deoxit worked like a charm on my car. thank Nigel

I had tried doing harness contact cleaning with Lectromotive & baking soda solution (compressed air in between to dry it out), but the P0380 code came back after a while.

Then, in trying to clean (via abrasion) the contacts, one of the small metal pieces (pictured above) fell out. I did manage to form it back into a cylindical shape, place it on top of the GP and insert the harness back on top of it (click). The code has yet to return in a week's driving back & forth to work, so we'll see if it's only temporary...

Don't get me wrong I am not saying not to try the simplest repair first and the guide to checking the system is great. My personal experience with my car is tried cleaning, new glow plug, dexoit, which I soaked in overnight. Goes away for a little while and comes back. If the simple solution doesn't work after 1 or 2 tries, then get a harness. The glowplug issue didn't cause any problems with my car, other than the annoying lite. My wife even put a chakita bannana sticker on the dash so she wouldn't see the lite. Of all the different solutions dexoit lasted the longest time, about 2 weeks. I even know of one person who took there car in for the brake lite switch recall and it cured the glow plug issue. I don't want to spend anymore on my own personal car than I have to or any else's car as well. If it is someone else's car I am working they have usually tried cleaning or other remedies. By the time it gets to me I replace the harness and problem is solved. I don't want to have people have to come back to me to work on their car again for the same problem. So I check the glow plugs, relay and if that is all good then replace harness.

Glow plug brands

If one of the glow plugs needs replacing (2001 ALH engine), does it matter what brand (VW OEM, Bosch, Beru), or whether all of the ones in the car are the same?

One parts vendor ( http://www.1stvwparts.com ) lists both "glow plug w/o plug heater" and "glow plug w/ plug heater" (VW OEM parts) for the same price. What is the difference, if any?

VW OEM _is_ Bosch or Beru... both of them were used by VW... (I believe they're close to identical as one of them is licensed from the other...)

I couldn't find the listing at 1stVW parts to which you referred... Try www.metalmanparts.com www.tdiparts.com www.worldimpex.com or www.dieselgeek.com Bleached Bora may also have some on special, but they may be a different brand...
http://forums.tdiclub.com/showthread.php?t=152185

As to whether to replace all of them or just the dead one(s)... depends on the vintage of your car... if all of the ones on your 2001 are original, I'd say they're probably ready for a replacement... if they're only a couple of years old, then possibly there was one that was destined for a short lifespan and can be replaced individually...

BTW: are you sure that the GP is dead and it's not simply a matter of corrosion inside the harness ???

Yuri.

After several attempts (harnesses, glow plug, sprays, Cu foils) to fix the glow plug CEL, I tried the following fix on a hunch - that was over 50K miles ago. No CELs since then! I think excessive vibration at the connection points is the source of poor contact.

Kedar

Well, your hunch was neither a winner nor a loser... just a tie...

Good idea that should help in many cases !!!!!

All the best,

Yuri.

I found out last week that there are 2 different styles of GPs used on the 2001 TDI engine - one by Beru, one by Bosch. They do not look the same. I don't have a dealership in my town, so when I went to one, I had to uncover the engine, look at the GP, and remember how it was shaped. One (I think the Beru) is longer on the inside of the engine. The parts person at the VW dealership I went to said they are not interchangeable. Be warned when buying online sight unseen, even if its for an ALH engine.

Miyagi said:

The parts person at the VW dealership I went to said they are not interchangeable.

Click to expand...

And of course, they're the most knowledgeable people in the world...

Many, many people have mixed Bosch and Beru plugs in the 2003-and-older TDI's without any ill effects... Every car's different, and there are other problems that can creep in, so the safest thing for a dealer to do is replace them all... (it also saves them time, and generates more revenu quickly...) (and if that doesn't fix it, they can then replace the harness as well...)

BTW: how much did that one glow plug cost you at the dealership ?? (Metal Man sells you 4 for $59... shipped... Bosch or Beru... your call...)

There has been less success mixing B&B with off-brands, but at the low prices, it's often worth replacing the set, especially if the glow plugs have a lot of miles on them...

Yuri.

harness

I just replaced a 4 wire harness on an 02 Jetta. Really a simple job. Remove the air box, lift the plastic cover on the vertical plastic box, driver's side, against the firewall, disconnect the 4 wire plug that matches the new one to the GP harness. Take off the old harness, snip off at the end, check glow plugs, clean tips, apply carbon conductive grease, put some in the new harness and press on the new harness. Wrap the wires where convenient and out of the way, plastic tie and then plug in the plug, replace the covers and it is done. I did not cut off the old plug, there is plenty of room for it in the box. This remedy is not as neat as opening the old loom, unwrapping everthing but you can be as neat as you care to tying up the new wires.

ahlcar, is it correct to use dielectric grease instead of conductive grease? I thought that if you apply conductive grease in a multi-wire connector, there will potentially be some leakage current. Thanks; Larry.

l_c said:

ahlcar, is it correct to use dielectric grease instead of conductive grease? I thought that if you apply conductive grease in a multi-wire connector, there will potentially be some leakage current. Thanks; Larry.

Click to expand...

I believe he's talking about putting conductive grease on the contact area inside the harness where it attaches to the glow plugs...

Dielectric grease, being an insulator, is useful on the sealing areas of the harness/glow plugs (to help keep out moisture)...

Yuri.

Question. Should the engine be completly cool before replacing a glowplug?
Thanks,
Kevin

Kevin, I'm guessing that it's mostly a safety concern, i.e. potential of burning yourself. If the coefficients of thermal expansion between the head and the GP body are similar, then I don't see that the temperature would make any real difference in removing. But when inserting a cold GP into a hot head, I guess it might tend to get over-tightened if you drive it in fast. I've recently started to use anti-sieze compound on various bolts and I think it's good to dab some anti-sieze goop onto the GP threads.

Also, today I finally put some solder onto my GP terminals, I hope that it helps to keep my MIL to stay off for a long time. You have to be careful not to leave any large gobs of solder on there, or else the harness connectors won't fit/seat properly. Also, the thermal resistance seems to be really low so you need to use a hot iron and try not to keep the GP terminal heated for too long. If this fix wasn't successful, I'll post a note here. Larry

thermographer said:

Question. Should the engine be completly cool before replacing a glowplug?

Click to expand...

I see you found the canned-worm opener...

Various highly respected experts here have said the following:

"I've found that the GPs come out a little easier on a warm engine."

"I recommend having the engine hot...then by the time you have the GP harness removed and tucked out of the way the engine has cooled off a little..."

"When screwing thing out of aluminum heads, let the engine cool overnight so that the head is stone cold before wrenching."

"Engine block must be warm."

"Never remove threaded parts or fasteners from warm or hot aluminum! Work them out carefully only when the aluminum is room temprature."


Clear ????

Some things on which people do agree:

"When I replace glow plugs I use high temp anti-seize paste on each GP"
(Copper-based is what I use, BTW...)

"Use a little compressed air to blow away any loose dirt around the GP base before removing it."

"(recommend) using a 1/4" Dr flex joint between the 10MM deep socket and the extention. This helps to ensure that the angle of the socket is aligned straight onto the GP. If you have the socket "cocked" on the GP then you might increase the risk of snapping off a GP"

"When you install the new Glow Plug use a thin film of high temp anti-seize paste and torque the new GP to 11Ft Lbs or 132 In Lbs. Don't even consider the idea of not using a torque wrench."

"10mm deep socket in 1/4" drive with a universal or wobble extension is needed. Use the 1/4" stuff so you don't exert excessive torque and snap off glowplug if you have an "UH-OH"

"Remove like a spark plug. If you have excessive resistance, turn SLOWLY to avoid stripping threads in head. Another reason for the 1/4" drive ratchet. You can also shoot some PB Blaster in the thread area prior to starting, if desired. I think it does help." (my comment: what's a spark plug ???)

"HAND-THREAD the glowplug into the head until it's snug."

"Treat your glowplug harness before reinstalling. DeOxit is good stuff."

"...learned from DBW in a similar situation: Don't work on your engine if it is filthy. Take the time to wash it down so there isn't a bunch of crud sitting around the holes to fall into the cylinder or get stuck in the threads.
Get the greasy dirt, and sand out. Especially when pulling the valve cover. I use "Gunk" brand cleaner, but sparingly, and just on real greasy areas. Simple Green works on less greasy areas. I did find out a couple weeks ago that if "Gunk" gets in between the engine and transaxle, the clutch will slip for a couple of weeks... Simple green is bad for aluminum. Mixed down not nearly as bad as straight. Brake cleaner works REAL well for small areas like this and then follow with compressed air BEFORE disassembly."

That's all that shows up on my computer right now... but it's late...

Yuri.

Another Glow Plug Question

Hi,

I have a '99 New Beetle. When starting my car, the glow plug indicator sometimes comes on (about one in ten times maybe) and otherwise does not. When it does not come on, the car obviously won't start.

I just finished replacing the glow plugs and wiring harness, but have the same problem.

Any suggestions? (Wiring connection to fuse box near battery, metal fuses, glow plug relay, coolant temperature sensor, or none of the above?)

Thanks,

Ken