VW Golf IV TDI glow plug operation?

Typical diesel starting is: 1) ignition on, 2) glow plug indicator comes on, 3) wait several seconds for indicator to turn off, 4) crank the engine to start. On my car, 1-3 happens; but, there is no power to the glow plugs. Funny though, when I am cranking, the glow plug circuit comes to life and it remains powered for roughly 45 seconds even if the engine starts. Many times on diesels, the glow plug remains on for a period of time to make sure the cylinder reaches sustaining heat. Is there a second circuit to power my glow plugs before I start cranking? I resorted to a manual house switch to preheat since my car was not working cold and it fired right up. Maybe there are two circuits that activate the glow plug. These new fangled computer cars have taken a relatively easily maintained device and made it practically impossible. I've gone to the VW dealer mechanics and found them unable to answer simple questions like this while being very good at taking a $20 job and charging $1,000. Anyone have a better grasp of my car's glow plug operation?


Update: This is summer with ambient temperatures of 50-70F. My internet searching has indicated the glow plug programming uses the coolant temperature anor inlet temperature in its decision process. I did find some air getting into the fuel line via a new/faulty fuel filter now replaced. On cold startup, the glow plug comes on during cranking and stayed on for 3 minutes. When the coolant temperature was warmed to 120F, the glow plugs stayed powered for 40 seconds. They did not come on nor stay on once the engine/coolant was at operating temperature. These glow plugs get red hot in a few seconds. I have no confirmation regarding any glow plug operation prior to cranking! Maybe its too warm, maybe it never preheats, and maybe a second something IS malfunctioning. There are also three glow plugs in the air intake of which the operation I know nothing at this point. The supersecret computer program and tight-lipped (or incompetent) local stealership makes all this a sort of blac

8 Answers

  • E
    Lv 4
    9 years ago
    Favorite Answer

    The ALH Engine glow plug system has three modes, Pre Glow, Start and Post Glow.

    Pre Glow heats the Air in the Cylinders to aid in engine starting

    Start Mode, Glow Plug are on during the start cycle

    After Glow, The Engine Glow Plugs are used for Emission and To maintain combustion in cold weather.

    Manual transmission Cars have an aux heating system installed to aid in bringing the engine up to normal operating temps, Which uses three glow plugs to heat radator Coolant up to temp. Cold Cabin in the morning, Replace these three Glow Plugs.

    Controled by a Glow Plug Relay and ECM in some cases.

    That is system operation in a nut shell. The Glow Plugs only last four years in cold climates, and are easily damaged from any fuel drips from leaky injectors (Hot spots/burns= No Good Bad Plug). If you have already change your glow plugs, and still have the starting issue your problem maybe a result of a failing Bridge. The Glow plugs may glow, but may not being enough amps to plug for a good start. The Bridge wiring breaks down over time and causes starting problems. Failing Bridges aren't really notice under you get cold weather. A muli meter wont tell you if the bridge is good or bad, a Megger is needed. In my maintenance Program, I replace the Glow Plug Bridge and Glow Plugs Together as a matched set.

    The GLow Plug Relay Rarely fails because it was remove from the eng area to under the dash. Replace only if the Glow Plugs and Bridge Replacement does not work. I also keep a spare bridge and Glows Plugs in the spare parts kit that is locate in the trunk.

    Source(s): 01 TDI Golf Fleet Operator, 209K Miles on Primary Golf, Avg. 20k miles a year with In house Maintenance.
    • Login to reply the answers
  • 9 years ago

    It definitely sounds like you're having an issue with the glow plug relay. On the US market cars, the large relays such as the glow plug relay are located on top of the battery.

    That being said. . . you really shouldn't even NEED the glowplugs to start a IV TDI, especially when its even relatively warm out. I know on my US market 2001 TDI (1.9L ALH) the pre-ignition glow plugs don't even kick on unless its below 50*F (15ish C) outside.

    The car should start up just fine without the plugs, makes me think you have some other underlying problem. Have you checked your timing? Even slightly retarded timing on a rotary pumped TDI can cause some nasty starting issues.


    Concerning your edit. The three plugs in the intake, are you sure they're in the air intake? Again, I'm only familiar with US market cars, but here the manual transmission cars had 3 glow plugs in the COOLANT hose right next to the engine block, on the right side if you're looking from the front of the car. These little guys really didn't do much of anything and were prone to failure, but I don't think anyone ever cared enough about them to find any diagnostics for them.

    If you continue to have issues, I would suggest going over to http://www.tdiclub.com and posting about your issues in the forums there. Dunno about across the pond, but it is far and away the greatest TDI information source in the US and there's always a ton of people online ready to help.

    Source(s): At this point though, if the car is starting up ok, I really wouldn't worry about the glow plugs. Hell, I drove my '01 Golf TDI in the commonly 10*F winter here in West Virginia without glow plugs for about a month, car was slow to start, but it would eventually come to life :)
    • Login to reply the answers
  • amaya
    Lv 4
    3 years ago

    Glow Plug Operation

    • Login to reply the answers
  • M M M
    Lv 7
    9 years ago

    The only thing i can tell you is to check the glow plug module relay, this seems to control most things on that, by your battery is the engine bay fuse box, first, the fuse in there F51 is for the glow plug module relay, attached to that fuse box or underneath it theres 5 relays, 3 on the top, and 2 on the bottom, the glow plug module relay is the middle one of the top 3, if its not to expensive you could try a new one of them, other than that get it checked out by an auto sparky, whether that module switches to another circuit or whatever on cranking , Dont Know?, Good luck with your vw from this side of the pond

    • Login to reply the answers
  • How do you think about the answers? You can sign in to vote the answer.
  • Anonymous
    5 years ago

    The easiest way to learn golf like a pro is by following "The Simple Golf Swing" program. It's primarily a 31 page eBook that teaches golfers how to make solid contact with the ball, how to avoid hitting fat, how to avoid slicing, how get more power, accuracy, and consistency in your swing. Consistency being the number 1 golf skill.

    You not only get the eBook though, you also receive a ton of extra material including video, lessons on putting, driving, chipping, sand play etc. Here is their official site: http://www.golfswingguru.net

    • Login to reply the answers
  • Anonymous
    9 years ago

    Is the glow plug relay in good shape? How about taking it to an independent VW mechanic?

    • Login to reply the answers
  • 3 years ago


    • Login to reply the answers
  • 9 years ago

    sadly I cant assist here as I think its a case of two relays or a relay and a timer being used. eg one to bring in power ( lamp come son) and second one to 'hold' power on for a set time according to conditions ( outside temperatures).

    try car club forums for your make and sites such as petrol heads.

    • Login to reply the answers
Still have questions? Get your answers by asking now.