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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 8957
Experience:  23 Years Caterpillar Engine experience.
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Have 91 topkick with 3116 cat engine intake heater was not

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Have 91 topkick with 3116 cat engine intake heater was not working . changed switch on engine . Is hot on one side and small wire is hot with key swich on but other side of switch does not get hot . Light stays on on the dash

Hi. Thanks for using JA! I will try and help you out.


The most common part that causes the Intake heater not to operate is the control module. It is the small black box on the top top the engine on the passenger side.


When you say you changed the switch on the engine, are you taking about the control module or something else?

Customer: replied 6 years ago.
Not the module . The guy at the cat place called it the switch . Is located right by the heater has two posts on top of it . He said it is normally a good start place
I see. That is the relay. It is also a possible cause of the heater not working but most of the time I find the Module bad. I would recommend replacing it.
Customer: replied 6 years ago.
Where is the module located on this truck
Do you know the engine serial number?
Customer: replied 6 years ago.
2bk04950 can i by pass module to see if it works

Thanks for the information.


I have not ever tried to bypass it. I'm sure it's possible if you can "Jump" the correct wires together.


The Module is located on the passenger side of the engine on the head kinda near the back of the engine. Here is an image of what it looks like.


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The part number is XXXXX

Customer: replied 6 years ago.
Run out and took a peek , not seeing it . Where is it at compared to the relay swich that I replaced . Must be right there somewhere

Sorry for the delay.


I was trying to find an image that shows it but I cannot seem to find one. There should be a wiring harness on top of the engine. There should be a small set of wires that come out of the harness and connect to the module.

Customer: replied 6 years ago.
I will go take another look
Customer: replied 6 years ago.
I followed wiring on top , it is towards drivers side . There is six wire go out and plug into this thing on the drivers side towards the back of motor . Has a bracket bolted to block and then this thing is held on with four screws is that the beast
Yes. That is it. My mistake. I told you the passenger side. It is on the drivers side.
Customer: replied 6 years ago.
What does it do , seems if I have power on the relay and the small wire that goes to relay when key is on that it would make other side of relay hot . Just wanting to make sure before I run out and buy that . It looks like it costs plenty
The control module has a timer in it for the heater. When the engine is started, the module gets a signal from the coolant temperature sensor in the thermostat housing. If it is cold enough, the module will allow the heater to come on. The module will cut the heater off when the engine gets warm enough or the module times out.
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