Forum | Marketplace | Knowledge Base | | H1 site | H2 site | H3 site
Click Here To Visit DC Auto
Click Here To Visit DC Auto
Click Here To Visit Hummercore
Click Here To Visit Hummercore
Click here for a listing of all HUMMER Network sponsors

Hummer Knowledge Base

The Hummer Knowledge Base

Testing the Glow Plugs

To check the Hummer diesel glow plug system. This procedure is written for the 6.5 NA Hummer engines. There may be slight differences in the turbo diesel engines, however the procedure described below should work. This procedure should not be used for military HUMVEE models, there glow plug circuit and controller is radically different from the Hummer models. Military HUMVEE owners should refer instead to the proper TO for testing procedures.

Tools required:

  1. Pliers, long nose.
  2. Small screwdriver
  3. Multi-meter (VOM) either analog or digital

Tools helpful:

  1. Jumper wire with a connector (spade, female) to match the Hummer glow plug.
  2. Jumper wire, with alligator clip for ground point

Glow plug test:

  1. Perform this test with key off!
  2. Set the multi-meter to ohms (conductivity) lowest scale (X1 is best)
  3. Connect one meter lead to a good ground point (use the jumper wire if necessary)
  4. Momentarily test the meter connections by grounding to another point the second test lead. The meter should read zero ohms.
  5. Remove the lead from the glow plug.
  6. Connect the non-grounded multi-meter lead to the glow plug. Use the #1 jumper cable as required.
  7. The meter should read low resistance, 0.8 to 1.0 ohms is the nominal resistance
  8. Any glow plug that reads high resistance should be replaced. The current glowplug specification is AC-60G.
  9. Perform steps 5 through 8 on the remaining seven glow plugs.

Glow Plug Power Distribution test:

  1. Perform this test with the ignition key off. Damage to the meter may result if the key is accidently cycled
  2. Set the multi-meter to ohms (conductivity) lowest scale (X1 is best)
  3. Connect one meter lead to a good ground point (use the jumper wire if necessary)
  4. Momentarily test the meter connections by grounding to another point the second test lead. The meter should read zero ohms.
  5. Remove the lead from the first glow plug. Do NOT remove the remaining seven glow plug leads at this time.
  6. Connect the non-grounded multi-meter lead to the glow plug cable connector.
  7. The meter should read low resistance, almost zero ohms is the nominal resistance
  8. Any glow plug cable that reads high resistance probably has a bad fusible link, and should be replaced.
  9. Reconnect the glow plug
  10. Perform steps 5 through 9 on the remaining seven glow plugs.
  11. Remove all glow plug connectors at the glow plugs.
  12. Connect one lead of the multi-meter to a glow plug wire (that passed the above test) on the left (driver's side) of the engine.
  13. Measure conductivity to any glow plug on the right (passenger's side) of the engine. This value should be zero ohms.
  14. If there is an open (no conductivity, high resistance) then one or both of the main glow plug controller output fusible links has failed. Replace the glow plug harness, or replace the fusible link as necessary.

Glow Plug Controller test:

  1. Set your multi-meter to volts, any scale that will you to observe about 12 volts, DC.
  2. Attach the multi-meter ground lead to a good engine ground.
  3. Remove the #1 glow plug lead.
  4. Attach the multi-meter to the glow plug lead.
  5. Turn on the ignition.
  6. Observe that there is about 12 volts at the glow plug whenever the wait light is illuminated, and that the glow plug controller makes a clicking sound as it cycles. (note: steps 3 through 6 may be repeated for each of the remaining glow plugs in place of the harness test described above.)
  7. If 12 volts is not obtained in the above test, did the glow plug wait light illuminate?
  8. If yes, the problem is probably a wiring fault on the glow plug controller's output (to the glow plugs) harness.
  9. If no, the wait light did not light, and the engine is cold, either the glow plug controller is defective or is not receiving the correct signals to turn on.

Note: Removal of failed glow plugs is easiest if there is a glow plug removal tool available.

Peter H.


  1. Get a 12V trouble light. Unhook any Glow Plug. Attach the aligator clip to the connector on any of the glow plugs. Put the sharp point of the probe into the connector. Have someone turn the ignition to on. Does the trouble light, light up? Is it of normal 12-Volt brightness? Repeat for other 7 Glowplugs...
  2. With a Multimeter set on Ohms, attach ground (-) of meter to a good engine ground point. Unhook a glowplug and measure resistance at the electrical connector on the glowplug with the (+)positive meter lead. Good plugs are less than an (1) Ohm although 2 or 3 Ohms is usually OK. If higher than that the plug is probably bad... Repeat for other 7 plugs.

Frank
96 TD Wagon


Back to main page

The Hummer Knowledge Base is a collection of informative posts from the Hummer Network forums and mailing lists, contributed material and links to outside web sites.
The Hummer Network is not responsible for the accuracy of the information contained herein or on outside web sites, nor for any situation arising from the use thereof.
2006-2011 by The Hummer Network. No material from the Hummer Knowledge Base may be reprinted or republished in any form without permission.