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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8864
Experience:  I am ASE Master Truck Certified.
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Mr. Cat Man, I have a 6NZ cat in a 379 peterbilt. None of my

Customer Question

Mr. Cat Man, I have a 6NZ cat in a 379 peterbilt. None of my check engine lights and stop engine lights illuminate when the engine runs hot or when I unplug any sensor,, however they do throw faults on cat et but nothing in the dash to let the driver know something is wrong. The lights do illuminate at initial key on. Best I can tell all parameter are set accordingly in et. At help with this issue will be greatly appreciated.
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.

If the lights come on at start up but do not come on when there is a fault. That sounds like a faulty ECM.

Both the yellow and red engine lights should always have 12 volts going to them. To turn on the lights. The ECM just applies a ground.

I would unplug a sensor and then verify there is 12 volts going to the light and that the ECM is giving a ground. The ground pin for the yellow light is pin 28. For the red warning light it's pin 29.

If there is no ground. The ECM is the problem. If there is no power. There's a power supply problem.

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

Customer: replied 1 year ago.

It seems that 28 and 29 are applying a ground even when they shouldn't be. I don't see how to check power supply to the light in the dash as it just a mother board with a bunch of bulbs.

Expert:  Cat Man replied 1 year ago.

I see. Thanks for the information. It sounds like the lights run through a circuit board and not directly like they use to. I would suspect the board may be faulty.

Customer: replied 1 year ago.

Where would you suspect those pin 28 and 29 go to before the circuit board?

Expert:  Cat Man replied 1 year ago.

To my understanding they should go to the board. I normally see them go directly to the lights. But since you have a circuit board. I would suspect it should go directly there.

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