View Full Version : How to test T1N glow plugs in head?

12-02-2013, 06:32 PM
Sorry if this has been covered elsewhere (I'm sure it has), but I can't find a definite answer on how and where to test a Glow Plug that's in the block. Lots of threads on how to remove them, how the new module is better than the old one and how to bench test them and other good stuff, but nothing on testing the plug while it's in the head (at least not that I could find).
My Bro-in-law just bought an '03 and shortly after he bought it, the glow plug light turned on and stayed on.
My DAD is currently dead, so I figured there's gotta be a way to test each individual glow plug without removing it.

12-02-2013, 06:47 PM
Two options spring to mind:
Resistance check - one with exceptionally high or infinite resistance is likely to be the problem one
Put an ammeter in line and see how much current each draws - suspect a faulty one will draw much more current. Few multimeters have ammeter function and most that do only do very small currents, I certainly don't have a meter to do this myself so would do a resistance check. Even without knowing design values there should be enough good plugs to do a comparative test.....

12-02-2013, 07:04 PM
Quick & easy answer , use a clamp on ammeter .

Wrap the wire around the clamp & get some one to switch on the ignition , no need to turn the engine over , If i remember correctly , each plug consumes about 5 Amps at working temp , So a reading of 5 -10 Amps will indicate a working plug . A heavier current draw or almost no current draw & BINGO you have you duff plug .

Hope it helps you

12-02-2013, 07:24 PM
Sears sells nice AC/dc clamp on meter for ~$60. Well worth having in your kit. Beware however that they also sell an AC only version that looks identical for nearly the same money!


Aqua Puttana
12-02-2013, 08:44 PM
We have such short memories here. A simple test from Herr Doktor himself for T1N glow plugs which uses a simple jumper wire with 20 amp in-line fuse. (Not to be used on the 4.5 volt [or there abouts] NCV3 glow plugs though.)

That is not the easiest or most accurate test for open glow plugs.

See my old original post for making a simple fused glow plug test wire.

Connect to each glow plug pin socket in the engine harness connector at the glow module, one at a time. Simply brush the clip you would normally clamp to the battery + post, across the + post, for each glow plug pin test.

Pins are numbered on back side of plug with an accurate glow plug location.

A strong, harsh spark (if you're quick) or a blown fuse (if you're slow) indicates a failed shorted plug.

A gentle brush of sparks ,and no blow 20A fuse in 10 second, indicates a operating glow plug.

NO sparking indicates a open circuit glow plug.

Easy to see in strong daylight.

Doktor A

As always the original post/thread can be accessed by clicking the blue arrow within the quote box.


12-02-2013, 09:14 PM
The new T1N glow plugs measure about 0.7 ohms resistance. They seem to be OK down to about 0.5 ohms. Anything outside of that range should probably be replaced. If you do Bill's glow plug modification, you can just pop out the fuses and read each one at the fuse block with a DVM.

Aqua Puttana
12-02-2013, 10:43 PM
... If you do Bill's glow plug modification, you can just pop out the fuses and read each one at the fuse block with a DVM.
Yep. Or just use Doktor A's fused jumper test lead to the fuse block.

Depending upon the failure mode, the ballast or control winding adds a bit of question to any resistance/ohms test. I believe that is why Andy recommends the 12 volt power test. I'm quite certain that he's not afraid of using an ohmmeter.

Personally I would just replace them all if doing it DIY.

My reasons.
Generally glow plugs have a finite life so replacement is almost inevitable.
Not much more added work or expense once you are set up for the process.
The longer the glow plug remains in place the more likely for it to sieze so removing all of them helps with that.



12-03-2013, 12:18 AM
I recently replaced my glow plugs in my 06 Sprinter with 160,000 miles or so. Likely the first time they have been replaced since this vehicle came from TX.

I used the 12v test lead with 20 amp fuse as suggested by others. At the glow plug module wire harness, 1 wire blew a fuse and all the others appeared to be open with no visible little spark as described. I also measured resistance to ground on all and 4 measured between .5 and .8 ohms, with the 5th being shorted to ground. After replacing all the glow plugs, I checked again and got a tiny spark on each one, without blowing fuse obviously. To me this indicates that measuring resistance to ground may not be a true indication of glow plug condition as there did not appear to be any current flow with no little spark observed.

BTW, thanks to all those who contribute to this forum, your help has been invaluable. I was able to get all 5 plugs out with relative ease, took me much longer just reading about how to do it and worrying I would break one. Getting the engine warmed up properly is VERY important (I initially tried it luke warm, using modest torque with 1/4 drive ratchet, only the 1st one loosened) and all came out easily with clean threads. I was skeptical at first having ruined threads in an aluminum head by taking a spark plug out of an air cooled engine that had just been turned off.

12-03-2013, 12:58 AM
Quick & easy answer , use a clamp on ammeter .

Yes, I really ought to buy one instead of always finding an alternative test and then never getting round to it!
I'm sure if I work on him long enough I can get the boss to buy a nice Fluke one for the LLL test kit and then I can borrow that :)

12-03-2013, 02:08 AM
My $15 Harbor Freight clamp-on has been working like a champ for ten years.

12-03-2013, 03:46 AM
My $15 Harbor Freight clamp-on has been working like a champ for ten years.

I just got a gift certificate to HF. Looks like I'll be using it! :thumbup:

12-03-2013, 03:48 AM
I just found this on Ebay for a Glow Plug Module:
"Tech Tip Description: Prior to replacing a glow plug that is shorted to ground (DTC 1482-001 Glow Plug Module , Excessive Current) double check which glow plug is affected. A DTC stating that one certain glow plug is open is NOT related to the above mentioned issue. The following test procedure helps to identify a shorted glow plug: Disconnect the 6-pin output connector of the glow plug control module. Use a 12 gauge wire and a 20 Amp in-line fuse to connect the positive side of the battery with one pin of the connector going to the glow plug. If the fuse burns out within 10 seconds, the glow plug is shorted. Repeat that procedure for every pin going to each glow plug. Check the pin number on the connector, pin 1 wire goes to plug 1 and pin 5 wire goes to plug 5. Bring engine to normal operating temperature prior to removing a glow plug. Warming up the cylinder head allows the glow plug holes to expand, which makes removal significantly easier."

12-03-2013, 06:06 PM
Here are a few images for checking the glow plugs.

I have some old Weston ammeters - A/C - D/C, rated up to 50A. I made some simple test leads - using a crimp on terminal for a probe - fit perfectly into the connector.

I removed the left headlight for access, disconnected the connector from the GP module under the battery. The numbers for the GP's are located on the back of the connector. The initial reading displays between 21 to 19 Amps and quickly drops.Total time to perform the check was 30 minutes.


12-03-2013, 08:54 PM
...so you put one wire on the + terminal of the battery, ran it through the ammeter, then the other end you hooked to the glow plug connector that is in the photo? And each good plug pulled 19-21 amps?
Thanks, Bruce.
Thanks for the pics, too. They are really helpful.

12-03-2013, 09:05 PM
Yes, just be careful with the test lead. A safer (and a little slower) method would be insert the lead into the connector, then attach it to the ammeter - less chance of a fireworks show if the lead is accidentally dropped.


12-05-2013, 05:19 PM
Yes, I really ought to buy one instead of always finding an alternative test and then never getting round to it!
I'm sure if I work on him long enough I can get the boss to buy a nice Fluke one for the LLL test kit and then I can borrow that :)

Love the optimistic outlook you have :thumbup:

12-06-2013, 12:23 AM
Love the optimistic outlook you have :thumbup:

Well, I did lend him my engine crane - in some respects it's handy not having it getting in my way in my garage, on the other hand he hasn't actually used it yet but is storing it securely in the server room at work, so it gets in my way there instead - I have to climb over it to change the backup tapes every week! :idunno:

12-07-2013, 04:49 PM
Ok, so I used the 20a fuse to test each plug. 3 of them blew the fuse and 2 of them were dead- no spark at the battery.
So it looks like I'm replacing all five. So...... where the heck ARE the glow plugs? I can't find any photos of their location here on the forum and google images wasn't helpful either. It *looks* like they are located in the block/head under the intake manifold, but I can't see well enough to know.
Those of you who have done this job, please advise!

12-07-2013, 05:27 PM

When standing in front of the van, they are on the right side of the valve cover above the intake manifold. Look for a wire harness with 5 black plug in connectors going towards the valve cover.

This link has some pictures, but the intake manifold is removed.

edit: you're in luck! The T1n just got home so I got a picture. This pic shows glow plugs 1 &2. The wire harness runs through a plastic loom on the right side of the head.

Aqua Puttana
12-07-2013, 06:36 PM
... Those of you who have done this job, please advise!
Look for wires with what looks like a spark plug cap on the end.

There's a drawn diagram here.



12-07-2013, 08:43 PM
Ok, ok. So Im readimg through Vics write up and he mentions that the earlier engines glow plugs may be more difficult to access. I pop the hood on my '06 and WHAM there are the glow plugs! Then it hits me that my bro-in-laws van is an 03 and my guess is that the intake manifold obscures the glow plugs. Ok. Now i know where they are, i guess ill bite the bullet and pop them out next week. Thanks guys!