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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
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Experience:  I am ASE Master Truck Certified.
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I have a f-750 with a c7 in it, the intake heater does not

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I have a f-750 with a c7 in it, the intake heater does not work. The wait to start lamp turns on but the relay does not click. I checked for power on the hot side and do have power, when key is turned I do not have power on the other side.
Hi. Thanks for asking your question! I will try and help you out.

The intake heater should have 12 volt power to the two pin connector on top of it. When the engine ECM wants the heater on, it simply applies a ground to the two pin connector to turn it on. If you have 12 volt power to the intake heater relay, you have either no ground being applied to the relay or a faulty intake heater relay.

Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 3 years ago.

the thing is when i use the battery post as my ground i have 12 volts at that 2 pin connector, but if i stick a paper clip in the green wire on the 2 pin connector and use that as my ground and stick my other lead into the red wire on that connector i only get 3-7volts. It should be reading 12, and I do not know why it is not. I'm stumped on this, it's not getting enough voltage to close to solenoid. I use the cat scan tool to manually turn on the intake heater. I only have 12 volts at the hot wire coming from the starter on the solenoid, not the other side where it goes to the heater itself.

Thanks for the information Grant.

If thats the case, I would suspect a problem in the wiring. Either the positive or the ground. There is most likely damaged wiring that does not have the correct amount of good copper to carry the load if the system to turn on the solenoid.
Customer: replied 3 years ago.

I ohmed out both wires when I disconnected the pcm and they only have 1-3 ohms through the power and ground wires, and they both have continuity when i plug the from the pcm to the connector itself.

Thanks for the information.

If that's the case and the wiring is OK, the only thing left is a faulty engine ECM. It is most likely not able to apply a good enough ground to activate the intake heater relay.

Let me know if you need more help.
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