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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8811
Experience:  I am ASE Master Truck Certified.
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I have a1998 c6500 3126 cat won't start and the check engine

Customer Question

I have a1998 c6500 3126 cat won't start and the check engine light won't come on when u trun the key on
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.

Thanks for asking your question and requesting me. I will try and help you out.

If the yellow check engine light does not come on when the key is turned to the on position and the engine will not start, there are only 2 things that can cause this.

The first and most common is the engine ECM is not getting the correct power and ground to function. The ECM should have power on pins 52, 53, and 70 of the rear most ECM connector. This is the truck side harness connector. 70 is the key switch wire. The grounds are on pins 65 and 67. You can remove the connector and check for power on these pins. If you do not have power on these pins, you most likely have a blown fuse in the electrical system. I would check all fuses first.

If you do have correct power and ground to the ECM, you most likely have a failed ECM. I have seen this many times over the years. To confirm the ECM is bad, you would need to install a known good ECM on the engine or you can take the ECM to the dealer to be tested. Unfortunately the ECM cannot be repaired. Replacement is the only option. I am sorry. I wish I had better news.

Please reply back if you need more help or have more questions. I am happy to assist.

Customer: replied 1 year ago.
Will the ecm off of a 2000 model work on this 1998 truck both c6500
Customer: replied 1 year ago.
U there
Expert:  Cat Man replied 1 year ago.

Yes it should. If you can get the the engine serial numbers off both engines in an confirm.

Customer: replied 1 year ago.
Ok let u no how it goes thanks
Expert:  Cat Man replied 1 year ago.

Ok sounds good. Keep me posted.

Customer: replied 1 year ago.
if the numbers r close will it work
Expert:  Cat Man replied 1 year ago.

As long as they are both 3126B engines. Or both 3126E engines. It will work. You just can't mix a 3126B with a 3136E.

Expert:  Cat Man replied 1 year ago.

Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

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