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Ivoskis August 12th, 2018 13:31

Glowplug relay on 2003 TDI Jetta. Where?
The glow plugs get no juice and hence no starting the engine. So I found a relay panel above the left knee of the driver but it is confounding me as it is different from as shown on my "generic" Chilton circuit diagram.

Also, could not find any group of 4 black wires with red, green, dark and light blue tracers as they come off the glow plug harness on the engine and then pass through the fire wall to the instrument cluster. The "100" labelled relay I assumed to be for the glow plugs has two heavy wide spade terminals for like 40A and two smaller ones for the solenoid. It ohm-ed out OK and clicks when powered too but I found no continuity from the sockets the glow plugs. Also, there were no mice chewing marks or burnt smell. My diagrams however show 2 two more but otherwise functionally similar relays with 4 contacts but my panel has some larger multicontact relays. Googling showed a longish rectangular relay, plus a squarish one, so which is which in the age of fake news? The car was Mexico assembled, if this helps t ID it.

Mirrors did not help me picking up this color scheme wiring below the steering wheel but I did trace the wiring from the GP's on the engine block to underneath the battery tray and then into a covered plastic channel about 2" wide. This hid a 4-pin connector with identically color coded wiring which then dives into the firewall to the instrument cluster area. All wiring appears to be intact and this problem only started after I replaced the turbo and cylinder top as the cam bearing were seized. The engine now starts and runs ok but only if I briefly McGiver 12V to the glowplugs directly. Only then will it will fire up.

Is this relay out of sight perhaps, accessible from above only? Too difficult to see as the harness is wrapped and there is other stuff in the way. There is also a small fuse-like 2-pin relay, which on opening up appears to be a thermal timed delay type, presumably for the glowplugs. The relay is is both quite visible and accessible with two heavy red wires to it.

Tdijarhead August 12th, 2018 19:11

On the 03 the relay is mounted up where the windshield meter is you’ll have to pull the wipers and remove the valance. It a 180 relay. Check for a picture.

Ivoskis August 12th, 2018 20:44

Thanks TDIjarhead, I will check that info out and let you know. The car is
not right with me and it will only be next week some time when I will be able to get to it.

wonneber August 12th, 2018 21:02

Did you check if the fuses on top of the battery are OK?
I think there are 2 fuses, 1 for two glow plugs.

Tdijarhead August 13th, 2018 03:34


Originally Posted by wonneber (Post 5432221)
Did you check if the fuses on top of the battery are OK?
I think there are 2 fuses, 1 for two glow plugs.

Wonneber is right. A no power glow plug issue is more likely that fuse panel on top of the battery.

There are 2 50A fuses there. Pull them off clean them up, check for any melting of plastic or other damage. Very common with that fuse panel.

Ivoskis August 13th, 2018 13:09

You know, I did check but only with my eyeballs and not with meter. (My bust!)

I've repaired and worked with electronics most of my life and those fuses looked pristine, as did the connections. No burnt or melted plastic and IMHO there should have been connection to 12V just by looks. High current ( like the plugs would draw ) does do funny things at times, so thank you for this tip. Per my available circuit diagram other stuff should also have failed if those big fuses had failed, or any of them, so I did not check further.

The little fuselike relay on the outside of the underdash relay board was o/c however, until I pried off the aluminum shielding can to wiggle the contacts. I thought I'd solved the problem at that point but no luck! Still don't know what that one does and it may well be a fail-safe part of the GP relay circuit, to prevent them staying on and burning out in case the main relay contacts welded shut.

oilhammer August 13th, 2018 14:28

Back the Fail Train up a bit.... why do you think you have a glow system problem?

The car won't start? Unless it is about 10 F, the car will start without the glow system working. It may be cranky and smokey and noisy if it is below 40 F or so, but it WILL start.

Do you have any DTCs? The ECU is VERY good at detecting and flagging faults with the glow system. If you have no DTCs related to that, you can rest assured your glow system is fine.

Ivoskis August 15th, 2018 13:57

Oilhammer, there is no voltage at the plugs, zip. Only when I directly wired 12V to the plugs with 14gauge wire does the thing start. On my boat I had a similar issue that the 3-cylinder Perkins did not start without the plugs working.

It may be a timing issue on the Jetta as well, as the head and timing belt were replaced and no software tune-up for advance/retard was done afterward, but even repeated attempts at cranking did not get things to run. Once the 12V was applied, no problem. ( The car is at 3300' altitude, so the air is a little skinnier there )

BobnOH August 15th, 2018 14:04

Might be the engine/controls are not in good shape. What is the temperature there?
I'm confident you can get the glow plug thing sorted out. Relays, fuses, wires all occasionally fail.

oilhammer August 15th, 2018 14:12

I don't care about the voltage at the plugs, I care if the ECU cares. If the conditions are not calling for a preglow, then there will be no voltage.

If there are no glow related DTCs, then your glow system is conditionally intact. The ECU monitors this. You need to find out what the ECU thinks the coolant temp is, and go from there. You are attempting a diagnostic strategy based on a false assumption. Perhaps there is some other issue with the engine, and an aggressive preglow is allowing it to start when it otherwise would not.

You can pull the CTS plug off, and the ECU will default to a full preglow, about 10 seconds or so (I forget).

You say you are at high altitude. That's fine. The ECU should know this. Does it? This data is available. Computers are dumb. Bad input means bad output. DTCs mean the ECU has flagged something, you still have not answered that question.

Ivoskis August 15th, 2018 14:40

Good point about the ECU calling a glow need. My cheepo code reader only gave me a single I think 0380 or was it a 0382 reading, can't remember so ignore this. The little code chart I have said something about a #3 cylinder misfire for that code.

However, the 12V did make the difference. Now, if that negated ANOTHER issue, I really cannot say. It may well be so but I am unable to tell. Do not have a laptop or fancy reader to monitor the ECU ( dont know about the CTS plug either, sorry! )

Figured if I can get the car into at least a limp mode a more competent or better equipped guru can then fine tune it. Ich Dummkopf vill chust sticken die hands in den pocketsen, votch z blinken lites und zen leaven den adjusten to den Experten.

Ivoskis August 15th, 2018 14:43

BTW Oilhammer: the coolant thermometer light was on previously. Adding a little coolant did fix this issue though and air temp was well above 85F.

oilhammer August 15th, 2018 14:48

It is very difficult, impossible really, to troubleshoot any modern vehicle without a suitable scan tool. There is just only so much guessing and parts swapping you can do.

The threshold for the ALH's preglow period is around 45 F, afterglow will happen at higher coolant temps, but that is after the engine is started, and that is a different strategy for cold engine emissions reduction and not for starting aid. But the parts that make it work are the same, and the ECU monitors this just the same.

The glow system is very simple, and pretty reliable, on these cars. Relays rarely fail. Plugs fail, and sometimes the harness, but both would give the appropriate DTC and are unlikely to cause a no start all at once because each plug would have to die at the same time, which simply does not happen.

If you have a really sick engine, or some really pooched injectors, or some other such issue, that will not allow the engine to make sufficient heat in the piston bowl during cranking, and adding an "artificial" preglow period where there would normally be none, and it lets the engine start, then that is not a glow system problem. That is an engine or fuel problem.

But even half million mile ALHs rarely have issue starting in moderate cold temps, let alone whatever temps you are experiencing in your area right now.

Ivoskis August 15th, 2018 15:41

Very true Oilhammer, I sure wish I had such a tool but then I'd also need the diagnostic code crossreferences etc etc etc. This all adds up!

The compression after the head xchange I measured at about 380psi, which seems to be about in the ballpark for a like 180k engine with just ground in valves that have not had a chance to fully seat yet. ( guessing here mostly and I only tested #one cylinder, just to see if I could get #1 firing with a hot glowplug. )

What do you suggest i should do at this point? There does not seem to be a real idling issue now but I did note a gentle slow surge and relax. Not all the hoses of air filter etc are on and this may not help that ECU to diagnose it all fully. Ck engine light I believe is also still on.

jettawreck August 15th, 2018 18:49

If you are anywhere where the ambient temp is above freezing and it "won't start w/o pre-glow" there is something really wrong. Either the compression is (very) low, injection timing is very retarded (not advanced enough), cranking speed is sub par, etc. Using/needing pre-glow in such temps is masking an issue not related to the GPs.
As Oilhammer said, if there was a fault in the GP system the ECU would be letting you know about it.

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