How To: Test Glow Plugs

Know how to test glow plugs is a must for any diesel vehicle owner. You can test your diesel glow plugs to ensure they're working properly. Each cylinder of a diesel engine has a single glow plug, and a harness supplies power to the entire bank of glow plugs. Diesel fuel under high pressure at high temperatures self-combusts, and in cold weather, glow plugs assist this process by heating the combustion chamber for cold starts. So it’s good to check glow plugs before cold weather sets in.

View the full job and shop supplies here: oreillyauto.com/diy-check-glow-plugs

Supplies Needed for This Job:
1. Safety Glasses: orly.cc/4e7cFKz
2. Gloves: orly.cc/3YKu3QZ
3. Socket Set: orly.cc/3Odkxji
4. Multimeter: orly.cc/4hT8Zyb
5. Pick Set: orly.cc/4hub3wT
6. Needle Nose Pliers: orly.cc/41V2Ht8

0:00 Welcome Back
0:46 Disconnect the Battery
0:56 Locate the Glow Plugs
1:00 Remove Obstructions
1:19 Disconnect the Plug
1:45 Test the Glow Plugs
2:03 Apply Dielectric Grease
2:10 Reattach the Connectors
2:16 Reconnect Tubes

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Transcript:
Raise your hood… and disconnect your negative battery cable… or cables, if you have two batteries.
Set them aside someplace safe where they can’t touch metal.
Locate the glow plug control module.
You’ll find it here on the passenger side valve cover, behind the alternator.
For access to the module, you’ll need to remove the hot-side intercooler tube.
Loosen the clamp… and disconnect the coupling attaching the intercooler tube to the top of the intercooler.
You may need a pick or flathead screwdriver to loosen the coupling.
Unclip the tube from the turbo using needle nose pliers to lift the retaining clip from both sides.
Once the intercooler tube is removed, you’ll see two large connectors… one black and one green.
In some models, the connectors will be pointed toward the firewall, but the module will be in the same location.
Remove the connectors by depressing the tabs… and pulling them away from the module.
Use a digital multi-meter to test the resistance in each glow plug circuit of the green connector.
Check the resistance of the multi-meter itself before doing the test… and subtract that number from the resistance of each terminal to determine its resistance.
To test the glow plugs, lightly touch each terminal with one multi-meter lead… and an engine ground with the other probe.
A properly functioning glow plug should read between point five and two ohms of resistance.
Once you’ve checked each circuit in the green connector, repeat these steps for each glow plug circuit of the black connector as well.
After testing each of the terminals, a tiny bit of dielectric grease can be applied to the connectors before they’re reattached.
Reattach the connectors to the module by sliding them in until the tabs click into place.
Use the retaining clip to reconnect the intercooler tube to the turbo.
Secure the other end of the tube to the intercooler with the coupling… and tighten the clamp.