Grid heater works to good

[MPalachuk]

Truck is a 1998.5 24 valve. The grid heaters come on and stay on to long, Even after the motor is warm. When it starts from cold it will pull the volts way down and stay there for 5 minutes. They do not cycle like I am used to seeing, the volts cycling up and down, They are just pulled down. New batteries, Clean cables and a new alternator. I also changed the air intake sensor with little, If any change.
If truck is warm and stop a the fuel station when you start it to leave the heater stays on like it is cold, It might not stay on as long after but still to long for normal. I can not find any info on what sensors control that system, Figured the iat sensor so it is changed and looking for other ideas.
So instead of the problem of them not working I have the problem they work to good.
Any ideas?

 

[gsbrockman]

Relays perhaps sticking some?

 

[BigPapa]

I agree, look at the relays. They’re below the driver side battery on the fender well.

 

[GAmes]

I can not find any info on what sensors control that system

The factory service manual has a complete description of how the grid heaters work. I prefer a printed manual, especially when chasing wires https://www.genosgarage.com/product/dfsm98-print/dodgeram-factory-service-manuals but the disc saves some money.
https://www.genosgarage.com/product/dfsm98-cd/dodgeram-factory-service-manuals

I agree there could be a sticking problem with the relays. The PCM controls the ground to them, so by disconnecting the ground trigger wire while they are engaged is an easy way to see. If the relays drop off line then the PCM could be faulty.

 

[MPalachuk]

The relays are not sticking, They are being told to stay on that long by the computer. The relays work as told.

 

[GAmes]

The relays are not sticking, They are being told to stay on that long by the computer. The relays work as told.

Then you have a PCM problem. Wiring the heaters to a toggle switch is an easy work around. Leave the hot trigger wires connected, disconnect the ground wires from the PCM and wire in a switch to ground.

 

[Bromiley99]

Do you have a check engine light? I believe if the control circuit is open there is a code that pops a CEL.

 

[MPalachuk]

No check engine light.

 

[Bromiley99]

Well if there isn’t one I think the control circuit is fine. If there was an open or short in the wiring or PCM you would have a CEL. What is making you think the relays are being told to stay on? What did you test?

 

[JMcCoy]

Are they both sticking on or just one? I disconnected mine when one stuck. I assumed it was the solenoid since it was just one. I have yet to address the issue since I live in South Florida and have a wife that doesn't like to leave the state in the winter. It hasn't been an issue yet but needs to be fixed.

 

[Joe Mc]

-MPalachuk, figure anything out?
-Everyone else, figure there's no real way for us to test/troubleshoot PCM? Wonder if a shop specializing in auto "electronics" could bench test? Or is only option the dealer, who most likely can only throw a new (if even available) at it? Quite the conundrum...
Found below online but like most other guys I just hate throwing parts and hoping that fixes whatever without first being positive.
https://dieselecm.com/products/dodge-cummins-isb-ecm-3942336?_pos=1&_sid=7c798d6b7&_ss=r
Sorry just realized, even though I searched "PCM" the link is for "ECM", WTF!
OK this place seems to have PCM
https://carcomputerexchange.com/dod...k-ecm-pcm-engine-control-module/prod_194.html