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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8679
Experience:  I am ASE Master Truck Certified.
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I have a 2003 gmc 6500 with a Cat diesel and a 6 speed.

Customer Question

Hi, I have a 2003 gmc 6500 with a Cat diesel and a 6 speed. Last week the battery was drained because the heater blower resistor went bad as I found when I put the battery charger on it. As soon as I turned the key on I noticed the glow plug light was not going out when it should. Also the cruise don't work now, along with the air pump. The check engine now flashes continusly. Somehow all this happened all at once and is tied together. Any thoughts?
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.
Thanks for asking your question. I will try and help you out.
Does the engine light flash while the engine is running? Or just with the key on?
The engine has no glow plugs. That light is an inlet heater light. Is it staying on all the time?
Customer: replied 1 year ago.
the light stays flashing while driving, and the heater light is staying on.
Customer: replied 1 year ago.
the truck also acts like the fast idle switch is on and explains the cruise not working.
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
The light flashing indicates an active fault code on the engine. Since the inlet heater light is staying on to, I must suspect a faulty engine coolant sensor or an inlet air temp sensor.
The reason I say this is because the inlet heater is controlled by the readings of these two sensors. The ECM adds the readings of the sensors together and turns the inlet heater on or off.
To verify. A service tool will be needed to read the codes.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
as I said in the intro. Something is tying all these problems together. I never had a problem until the battery went dead from the blower resistor. Heater light stays on, cruise don't work, engine light flashing, no air compressor working, acts like the fast idle switch is on but not in the mode.
Expert:  Cat Man replied 1 year ago.
Thanks for the information.
You may have a ECM issue. The ECM controls the cruise, inlet heater, fast idle, and engine light. I would try having the ECM read with a service tool. If the ECM is faulty. A service tool will verify.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 1 year ago.
what is this service tool you speak of? And do I have to go to a cat dealer/ I have a snap on solus pro if there is a place to plug in on this truck.
Expert:  Cat Man replied 1 year ago.
Cat ET software is the best tool to use. It's possible your snap on tool may work but I belies its limited on capability on Cat engines. But it's worth a try. The connection should be under the dash. It's a GM connector.
Customer: replied 1 year ago.
I will try this and get back to you.
Expert:  Cat Man replied 1 year ago.
Ok sounds good. Keep me posted.

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