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VEHICLE WOULD NOT RUN OVER 49MPH AND REVERSE GEAR WOULD NOT…

Customer Question
VEHICLE WOULD NOT RUN...

VEHICLE WOULD NOT RUN OVER 49MPH AND REVERSE GEAR WOULD NOT RUN, I CHECKED TRANSMISSION OIL LEVEL WHICH IS GOOD, I HAD NO PRIOR SIGNS OF TRANSMISSION FAILURE, I CONNECTED OBD AND FAULT CODE P0776 IS ACTIVE.

Mechanic's Assistant: Have you checked the level of your transmission fluid? Is it bright red, or is it dirty?

ITS CLEAN I REMOVED TRANSMISSION OIL PAN FOUND NO TRACES OF SHAVINGS OIL LEVEL WAS FULL PRIOR TO REMOVING OIL PAN.

Mechanic's Assistant: What is the model/year of your GMC?

07 GMC YUKON DENALI 6.0L

Mechanic's Assistant: Are you fixing your Yukon Denali yourself? What have you tried so far?

YES I WAS PLANNING TO REMOVING THE CONTROL PRESSURE SOLENOID B AND ALSO CLEANING VALVE IN THE VALVE BODY.

Submitted: 4 months ago.Category: GMC
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Answered in 7 minutes by:
3/22/2018
GMC Mechanic: Pete, GMC Mechanic replied 4 months ago
Pete
Pete, GMC Mechanic
Category: GMC
Satisfied Customers: 33,014
Experience: GM training and dealer tech for 14+ years. Diagnostics
Verified

Hi, my name is ***** ***** I will be happy to assist with this today.In some cases, I may need more info to assist better.I apologize for any delay.
I am here Sundays through Thursdays from around 5 am to 2 pm Mountain time.If you respond and I do not respond back right away I will do so as soon as I can.

This condition may be caused by a cracked 1-2-3-4 / 3-5-R clutch housing in the transmission.There was a bulletin released with this code being one of the codes that sets with this fault here.The bulletin number is # 09-07-30-004J.Inspect the 1-2-3-4 / 3-5-R clutch housing for a possible cracked weld. The housing can be inspected either assembled or disassembled.The transmisison has to be taken apart to remove this housing to inspect it.The parts are listed below.

https://www.dropbox.com/s/ha0dba6ogg9xqgo/ho-03-22.png?dl=0

Below is the diagnostic procedure for this code to help pinpoint the fault.

https://www.dropbox.com/s/wmsqhl4266z4rxe/p0776-03-22.pdf?dl=0

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service, your 5-star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.I work on delivering the best answer and help here but in some cases, it can be difficult to do without seeing the vehicle.

Thanks Pete

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