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vwnewton, VW Owner,ASE Master and L1 Advanced
Category: VW
Satisfied Customers: 307
Experience:  25 years of VW obsession turned into a job, last 15 years as a VW Tech.
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Glow plug will not stay on more than a few seconds when the

Customer Question

Glow plug will not stay on more than a few seconds when the ignition is turned on. It is hard to start and worse as the temperature drops. I have replaced the glow plug wiring harness, the glow plug relay, the temperature sensor and it still does it. If I disconnect the temp. sensor they will work.
JA: Have you checked the connectors on the sensor itself? It's important that they not be loose or corroded.
Customer: Yes all appear to be in good condition. I have checked all the wiring I can think of. It is a a 1998 Jetta TDI also by the way. AHU engine code. I am stumped at this point.
JA: Are you fixing your Jetta yourself? What have you tried so far?
Customer: Yes I am fixing it myself. It had a code in it for "glow plug monitoring intermittent" and i've checked everything I can find related to that with no luck
JA: Anything else you want the mechanic to know before I connect you?
Customer: No that i can think of. This problem is new it has worked fine in the past
Submitted: 8 months ago.
Category: VW
Expert:  Wolfgang replied 8 months ago.

Thanks for choosing Just Answer . I'm Wolfgang here to help!!

I am confident we can resolve your problem together. Please
understand that I don't know your skill level. In most cases when you have a problem
with the way the vehicle performs, specialized tooling is required to acquire computer
data/information or engine testing results. We didn’t build these complicated vehicles; we
just diagnose and fix them. Also understand that I can't see, smell, hear, or touch the
vehicle either, so it may take a few replies to get to satisfactory results. Note there may be an issue where the complexity of the issue will require a Premium Service. This service will be an addition to the normal question cost. Usually it does not come down to this but keep in mind!! I am also going to direct you with the fastest, easiest and most common things to check first. Please be
patient and permit me to do what I do best.
I also try to give all of the information you may need, expecting a “positive rating” in
return. I will also continue assisting you after you have rated me, if necessary. If there
is any reason I cannot get a positive rating, please let me know why “in advance”, so I
can go another direction for you. I am sorry you’re having this problem; I’ll help you
through it.
Below is my first answer or request for more information. If you do not understand it, or you need more information from me, or need me to go in more detail.

I do need some more info please

  • does the engine crank slower than usual?
  • what is the electrical resistance of the glow plugs?
  • when was the last time the fuel filter was replaced ?
  • how many miles on the vehicle?
  • i do need a vin # of the vehicle


Customer: replied 8 months ago.
VIN# ***** *****
Engine cranks normal. It will start fine with the temp. sensor unplugged to make the glow plugs cycle longer.
The glow plugs are fairly new, also replaced the glow plug relay, glow plug wiring harness, and temp. sensor
208000 miles
fuel filter was replaced approx. 2 months ago.
Expert:  Wolfgang replied 8 months ago.

ok the code do you have the fault code # ? either the 5 digit sae # pr the Pxxxx # will do

while you answer this question , Let me get the factory information on your vehicle

Customer: replied 8 months ago.
Don't have the code number but its was "glow plug monitoring intermittent"
I think it was P0150 but that is from memory and might not be accurate.
Expert:  Wolfgang replied 8 months ago.

ok when was the last time the timing belt was replaced?

Customer: replied 8 months ago.
It was done about 40000 miles ago.
Expert:  Wolfgang replied 8 months ago.

did you do the belt with the special tools and then fine timed it with VAG com?

Customer: replied 8 months ago.
it was done by a VW technician
Expert:  Wolfgang replied 8 months ago.

ok did you inspect the fuse for the glow plugs itself? the fuse is a strip fuse. it tends to deteriorate and have contact issue .

Customer: replied 8 months ago.
all fuses are good. The fuse on the fuse block at the top under the dash and the fuse on the firewall under the hood are all good.
Expert:  Wolfgang replied 8 months ago.

i wonder that the intake is clogged with carbon build up causing a breathing issue !!

Customer: replied 8 months ago.
No. It has to be an electrical or sensor issue. The car runs fine after its started. The glow plugs works fine with the temp sensor unplugged. I have tried a couple temp sensors and it makes no difference.
Expert:  Wolfgang replied 8 months ago.

under stand that but think about this ... at cold start up yes you have glow plug operation to heat the cylinder for the fuel for ignition. but you need air and a restriction especially when cold will cause a real hard start. once running you have the heat and air but while running much easier to ignite than on slow crank start .. that has to be really considered.

Customer: replied 8 months ago.
I understand that but the problem is my glow plugs will only stay on for a couple seconds unless i disconnect the temp sensor. Once i do that it defaults to a max glow plug cycle and it starts fine. The intake is in really good condition. I cleaned it less than 20000 miles ago when the turbo was replaced. Plus the code is a glow plug monitoring code. I would assume that something within that system triggered that code.
Expert:  Wolfgang replied 8 months ago.

thanks for the extra info !! it helps to know what has been done to the vehicle to narrow the issue!!

what is the temps in your area ?

Customer: replied 8 months ago.
The tempsare getting into the 30'sand 40' with some night time temps getting to the 20's
Expert:  Wolfgang replied 8 months ago.

OK with this there is diagnosis pinpoint needed and will take a premuim service to assist you with this . please premuim service offer .

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