How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Danny Your Own Question
Danny, VW Mechanic
Category: VW
Satisfied Customers: 4004
Experience:  ASE Master Certified with L1 Certification, Volkswagen Certified, VW and Audi repair shop owner
Type Your VW Question Here...
Danny is online now
A new question is answered every 9 seconds

2003 jetta tdi: glow plug light..light comes..glow plug harness..relay

Customer Question

2003 jetta tdi glow plug light comes on for only 2 seconds unless coolant temp sensor is unplugged. Replaced coolant sensor, thermasat, glow plug harness, and relay. Checked glow plugs with test light from battery positive to glow plug test light comes on. Still same problem unless I unplug coolant temp sensor than it cycles correctly. Not getting power to end of coolant glow plug harness. Sometime when I remove key from ignition switch it does not click or disengage interior lights dont come on put key back in turn key to on than off with pressure on it when I remove it and it clicks off and interior lights come on. Could bad ignition switch be related to this problem? Thanks Sal
Submitted: 7 years ago.
Category: VW
Expert:  Danny replied 7 years ago.



If you know you're having a problem with the ignition switch I would focus on fixing that first before messing too much with the glow plug system. There are may different circuits the ignition switch activates and it is theoretically possible that the switch could be affecting glow plug operation.


Also as far as the glow plug light goes how long are you expecting it to come on for when you turn the key to the run position to let them warm up before starting?



Customer: replied 7 years ago.
I will take you advice and start with ignition switch. On cold northeast days the light would stay on for 6+ seconds. If changing switch does not solve problem do I have to pay for more advice. Thanks Sal
Expert:  Danny replied 7 years ago.

Just don't hit the accept button until the problem is fixed and you can come back here to this thread. One last thing though can you tell if it's the mechanical portion or electric portion of the ignition switch? I'm unclear if it's the electrical portion of the switch failing or if the mechanical cylinder isn't correctly activating the electrical portion.



Customer: replied 7 years ago.
Good point. The clicking sound that I sometimes dont hear when removing key and that is accompanied by no interior light sounds to me like it may be more related to the mechanical cylinder
Expert:  Danny replied 7 years ago.

Ok, in that case I'd maybe try to lube the cylinder a little or something. Another thing is the glow plugs are controlled by the engine computer so if the light isn't staying on after you start the car (indicating a fault) then their probably isn't one and you're just noticing normal operation of the vehicle.

Customer: replied 7 years ago.
Have own the car since newXXXXXis a 2 second glow plug light preheat normal in 10 degree weather followed by a ruff smokey idle at start. Also as I stated in earlier post no power to coolant glow plug harness which is not controlled by ecm. Before problem occurred in cold weather a 6+ second glow plug preheat would be followed by a smooth smoke free start.
Expert:  Danny replied 7 years ago.

Ok, well you didn't mention the rough smokey start. What do you mean by coolant glow plug harness. Are you just talking about the harness that goes to the glow plug? Are you getting power to the glow plug harness. Also have you checked faults in the engine computer?




Customer: replied 7 years ago.
Besides the 4 glow plug that are used to assist combustion on cold days there is also 3 glow plugs in the heater jacket that helps heat the coolant. Each has it own harness. When coolant sensor is unplugged glow plug light on dash seem to cycle for 10-15 seconds. To avoid rough starts I leave it unplugged count to 6+ depending on temp and car starts as normal. From what I understand by unplugging the sensor the ecm thinks it cold and cycles the glow plugs for a long time. Before I change coolant sesor cel code was for high voltage output coolant sensor. After I changed sensor problem remainded the same.
Expert:  Danny replied 7 years ago.

Ok, I'm getting a better picture now of the situation. So, what you're saying about unplugging the coolant temp sensor is correct it just assumes that you're open circuit. Where did you get the temp sensor and do any faults remain if you erase faults and then drive the car around for a little bit. I know you stated you aren't getting power to the harness for the coolant but what about the normal glowplug harness.





Customer: replied 7 years ago.
Got the sensor brand new from a online part store. Yes I get power to the harness with the sensor unplugged making for normal starts. After I installed new sensor did not erase faults because problem remainded the same. If problem was solve and cel remained than i was going to clear cel.
Expert:  Danny replied 7 years ago.

You need to erase faults when you make repairs or the computer can continue to rely on old values sometimes. I'm not sure that would make a difference in this case. Is your sensor an OEM sensor? It is possible to get bad parts even new when they're discount parts. You don't have the ability to read temperature with your scan tool do you? You also could have a problem in the connector for the temperature sensor wiring or connector have you checked that? Erase faults and see if the fault returns.



Expert:  Danny replied 7 years ago.
Did the fault return after erasing it?


JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
< Previous | Next >
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
  • used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future. David L. Richmond, TX
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil Marysville, CA
  • Lurch. Thank you very much. I had real doubts about this website but your promptness of response, quick followup and to the point answer with picture was incredible. Charles Walnut Creek, CA
  • As a single woman, I really appreciate an excellent and affordable opinion.
    Thank you Geordie, I will not hesitate to contact justanswer in the future!
    Sue Charleston, WV
  • Another great insight to what may be the problem. I will have my mechanic take a look at it tomorrow. Thanks again, do indeed know your stuff. Jim Castleberry, FL
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK

Meet The Experts:

  • vwnewton


    VW Owner,ASE Master and L1 Advanced

    Satisfied Customers:

    25 years of VW obsession turned into a job, last 15 years as a VW Tech.
< Last | Next >
  • vwnewton's Avatar


    VW Owner,ASE Master and L1 Advanced

    Satisfied Customers:

    25 years of VW obsession turned into a job, last 15 years as a VW Tech.
  • VWDoc's Avatar


    Independent VW Shop owner

    Satisfied Customers:

    20 years of experience working with VW's. Independent European shop owner and technician.
  • Martin's Avatar


    auto electrical

    Satisfied Customers:

    South African Trade Diploma in Auto Electrical
  • Matt's Avatar



    Satisfied Customers:

    Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
  • Tim's Auto Repair's Avatar

    Tim's Auto Repair


    Satisfied Customers:

    Have owned a repair shop for 25 yrs.
  • Tim Mohr's Avatar

    Tim Mohr


    Satisfied Customers:

  • VW Tech 1's Avatar

    VW Tech 1

    VW Technician

    Satisfied Customers:

    ASE Master Tech, Master VW Factory Tech