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Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 4373
Experience:  Owner at DJ Wilson
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2001 GMC T8500 with CAT 3126, intermittent check engine

Customer Question

2001 GMC T8500 with CAT 3126, intermittent check engine light, engine loss of power after running for aprox 1 hours. Can not connect with Prolink Ultra, can not see any modules on the network. No wiring diagrams available.
Mike M
Submitted: 3 months ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 3 months ago.

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

The most common thing that causes this is a faulty in the injection actuation pressure system. I see this all the time. But to confirm, the ECM will need to have the codes read.

If your truck has cruise control, you can pull the codes by using the cruise control switches. If you have never done this, here is how.

Use the following procedure to retrieve the flash codes from the check engine light:

1. Turn the ignition key switch to the On position/ Engine OFF.

2. Turn the cruise control ON/OFF switch to the OFF position.

3. Move the SET/RESUME switch to either position. Hold that position until the yellow lamp begins to flash.

The yellow lamp will flash in order to indicate a two digit flash code and the SET/RESUME switch may be released. The sequence of flashes represents the system diagnostic message. Count the first sequence of flashes in order to determine the first digit of the flash code. After a two second pause, the second sequence of flashes will identify the second digit of the flash code.

Any additional flash codes will follow after a pause. These codes will be displayed in the same manner. Flash Code 55 indicates that No Detected Faults have occurred since the ignition key switch has been turned to the ON position.

Let me know what 2 digit code you get and I can tell you what the problem is.

Customer: replied 3 months ago.
Good Morning,This truck is not equipped with cruise control.Mike
Expert:  Cat Man replied 3 months ago.
I see. Thanks for the information.
Yeah many GMC and Chevys do not have cruise. Sorry.
Also many times Prolink tools are not compatible with the 3126 or C7 engine. Unfortunately you will need to have someone with Cat ET software read the ECM. I am sorry.
But most often the problem you described is caused by an injection actuation pressure system problem. I see this all the time.
Please reply back if you need more help or have more questions. I am happy to assist.
Customer: replied 3 months ago.
Our Prolink Ultra is loaded with 2 versions of CAT software that is registered and I have been successful with scanning other CAT engines. I'm concerned that I cant even see the ABS module on the network. Do you have access to wiring diagrams for this vehicle?Mike
Expert:  Cat Man replied 3 months ago.
I see. Thanks for the information. Sorry I do not. I will opt out and see if another expert can help.
Expert:  Daniel Wilson replied 3 months ago.

Hi my name is***** will be glad to help you with some diagrams. Click on this link to access.

diagrams

Customer: replied 3 months ago.
Thanks for your help Cat Man.Hi Daniel, Any diagrams available for module to module communication?Mike
Expert:  Daniel Wilson replied 3 months ago.

Hi Mike. What transmission model is in this truck?

Customer: replied 3 months ago.
It has a manual transmission in it.
Expert:  Daniel Wilson replied 3 months ago.

Thanks for the update so there is not a TCM as would be for an Allison. Click on this link for the engine side of things.

Troubleshooting

Customer: replied 3 months ago.
Should I also see an ABS module on the network? Also I cant locate the 9 pin round cab connector, I've only found the 16 pin OBD II connector.
Expert:  Daniel Wilson replied 3 months ago.

What is the serial number prefix of your engine? The first three digits?

Customer: replied 3 months ago.
CKM
Expert:  Daniel Wilson replied 3 months ago.

Thanks for the update. That is the correct engine diagram. The ABS has a separate module.

Customer: replied 3 months ago.
Hi Dan. Today was my first day back to work since Friday. Picking up were we left off, the link to the diagram is no longer active. I'm not making much headway on communicating with this truck.
Expert:  Daniel Wilson replied 3 months ago.

Thanks for the update. Do you have access to anyone that has Cat ET? I am wondering if you have a datalink or diagnostic connector harness problem. If Cat ET wont connect it would either be that, Loss of power or ground to the ECM or a faulty ECM.

Customer: replied 3 months ago.
There is a mobile guy that comes to us that has it. I can see if he can scan it. I'll get back to you.
Expert:  Daniel Wilson replied 3 months ago.

Okay, Keep me posted.

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