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7.8 liter duramax lights flash and truck goes into a limp…

Customer Question
7.8 liter duramax lights...

7.8 liter duramax lights flash and truck goes into a limp mode

Mechanic's Assistant: What is the complete model and serial number of your machine?

VIN 1GDK7C1345F514397
2005 GMC 7500

Mechanic's Assistant: Are you fixing this yourself? What have you tried so far?

Ive had other shops look at it. Say they located a bad wire in a harness and repaired, a boost sensor changeout and a pm. Im still at the same place

Mechanic's Assistant: Anything else you want the equipment mechanic to know before I connect you?

Under 100k miles automatic

Submitted: 4 months ago.Category: Medium and Heavy Trucks
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Answered in 46 minutes by:
2/15/2018
Technician: Steven, Shop Foreman/Triage Tech replied 4 months ago
Steven
Steven, Shop Foreman/Triage Tech
Category: Medium and Heavy Trucks
Satisfied Customers: 58
Experience: Volvo/Mack Master Tech, Certified with Cummins, Eaton, GM, Hino, Detroit Diesel
Verified

Hello, My name is***** am very familiar with the 7.8L engines. You are having an issue with it going into limp mode I see. Do you have any faults you were able to pull or get pulled out of it? There are numerous issues that can arise to cause it to go into limp mode. A fault code would allow me to isolate it down and point you in the right direction. Please let me know. Thanks

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Customer reply replied 4 months ago
The truck throws no codes
Customer reply replied 4 months ago
Im more than likely not the one to fix the truck. Ill probably have a mechanic do it. I thought giving him some steps would be helpful to him. Writing it down, I can bring with for him to see. I have replaced this truck with a new one and want to sell it. I just don't want to sell it with a problem. Id rather have it fixed right before offering it up for sale
Technician: Steven, Shop Foreman/Triage Tech replied 4 months ago
I understand completely. If you are able to get the current faults out of it I would be able to give you steps to remedy the issue. I see that you had a pm done so that should eliminate a fuel delivery issue. This being a c-series hopefully they replaced both fuel filters on it. If rail pressure drops down it can go into limp mode. I assume the oil pressure is staying up? The 7.8l has always ran pretty high oil pressure, especially when cold. There is also items on the Allison trans side that can put it in limp unless this is equipped with a manual. I haven’t looked it up in gmvis to see. If you are able to get the faults let me know and I’ll be more than happy to get you or someone working on it pointed in the right direction.
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Technician: Steven, Shop Foreman/Triage Tech replied 3 months ago

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Steven
Steven
Steven, Shop Foreman/Triage Tech
Category: Medium and Heavy Trucks
Satisfied Customers: 58
58 Satisfied Customers
Experience: Volvo/Mack Master Tech, Certified with Cummins, Eaton, GM, Hino, Detroit Diesel

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