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ironmike, ASE Master tech
Category: Chevy
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Experience:  30 years ASE Master L1 GM certified
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I have a 83 Chevy diesel. The glow plugs cycle on and off at

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I have a 83 Chevy diesel. The glow plugs cycle on and off at diffrent times. I can be driving all day and the glows will cycle as I am going down the road. Will by passing the controller stop this cycling? and how do I by pass the controller.


you might have some glow plugs that need to be replaced. An easy test would be to remove the connector and run a test light. Put the clip end on power and the tip/light side to the glow plug top(where connector goes). If the test light come on it is good, if not replace each glow plug. I would start there and then we can continue.

good luck

Customer: replied 6 years ago.

The truck starts fine and the glow plugws are all working. The truck can be up to tempture for hours and the plugs will cycle on and off (and some times tye won't). Some time I have to pull off the road and stop the truck to stop the cycleing so it will not run my battries down and burn the plugs out. That might fix the issues the rest of the day or ony for a few minutes. Being the the systme uses compression to explode the diesle/air mixture and not a spark plug. I think the problem has some thing to do with the controller of the glow plugs. I'm thinking that if I take the controller out of the loop and put in a manuel controlled switch that should fix the problem. I just need to know how to do it.

this is a check for the thermal controller, if you don't do this you can try the next instructions


  1. Disconnect electrical connector from thermal controller.
  2. Measure resistance between controller terminals using high impedance, digital ohmmeter set on 200 ohms scale.
  3. Resistance should be as follows:

Pins 2 to 3................0.40---0.75 ohms
Pins 4 to 5....................24---30 ohms
Pins 1 to 5..................117---143 ohms
Pins 2 to 6.............Continuity (0) ohms

  1. If resistance values are not as specified, controller is defective.
  2. If resistance values are within specifications, reconnect electrical connector and observe controller operation with ignition key in on position and engine stopped.
  3. If controller cycles more than one time, controller is satisfactory.
  4. If controller cycles only once, check for a short or open in harness as outlined in ``System Diagnosis.''
  5. If all other components are satisfactory, but controller cycles only once in step 5, replace controller and recheck system operation.

there is a factory fix for this. This is from alldata.

Number: 83-137 Section: 6D (VI) Date: June, 1984 Subject: INSTALLATION OF GLOW PLUG SYSTEM INHIBIT SWITCH - 6.2L DIESEL ENGINES


Model and Year:1982-83 "C-K-P" TRUCK 10-30 SERIES AND 1983 "G" VAN 10-30 SERIES


Many times, a 6.2L diesel will not require glow plugs to start, such as a warm engine or warm climate.

To inhibit glow plug system function when engine coolant temperature is above 125~F, the following parts can be installed.


Inhibit wire assembly; should be assembled per attached drawing (Figure 3).
Figure 1A

Figure 1B



1.Disconnect batteries.


2.Replace cover on R.H. rear head (Figure 1A) with cover, P/N 14028949 (same as on L.H. head) (Figure 1B). Use new gasket, P/N 14028951. Drain coolant as required.


3.Install new temperature switch, P/N 15599010 (with socket wrench, do not use open end wrench) using appropriate pipe thread sealer. Tighten to 19-27 N-m (13-20 Replace any lost coolant.


4.Connect glow plug inhibit wire assembly to temperature switch.


5.Route the wire assembly toward the left side of the vehicle, strap to the engine harness as required.
6.Disconnect the 4-way engine harness connector from its mate on the glow plug relay extension harness, P/N 12031493 (Figure 2).
7.Remove the light blue wire female terminal from the engine harness 4-way connector and install connector body, P/N(NNN) NNN-NNNN on this terminal. Plug mating connector on new jumper wire assembly (light blue/black stripe) to P/N(NNN) NNN-NNNN


8.Insert female terminal (light blue wire) of jumper wire assembly into empty cavity of 4-way connector. Reconnect 4-way connectors.


9.Reconnect batteries.
good luck
ironmike, ASE Master tech
Category: Chevy
Satisfied Customers: 3376
Experience: 30 years ASE Master L1 GM certified
ironmike and 5 other Chevy Specialists are ready to help you
Customer: replied 6 years ago.
I will give it a shot. Thanks for your help.
anytime, glad to help

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