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I have a 2003 GMC c7500 that has no codes but when it starts…

I have a 2003 GMC...
I have a 2003 GMC c7500 that has no codes but when it starts to reach highway speeds it drops into limp mode and a dash light that looks like a speedometer gauge at the top left of the dash comes on. When the truck drops to lower rpm the light goes out. I believe it is the cruise control light. It has cruise control buttons but no cruise, it works with the PTO to increase the rpms. I believe it has something to do with the PTO but I am not very familiar with them and not sure where to start.
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Answered in 19 minutes by:
1/18/2018
Wayne
Wayne, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 11,337
Experience: worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling
Verified

Hi I’m Wayne

I will Be assisting you with this issue today

yes you are correct that is the cruise control light

but what you are describing is the ECM(computer)

is acting up, I have seen this before, you will need to have the ECM flashed, or replaced

I hope this helps you

Wayne

My goal is to give you the best experience possible! I hope I have earned a 5-star rating! Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave today. If you need more assistance, please use the reply box and let me know.

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Customer reply replied 7 months ago
Am I right in assuming that the ecm believe that the pto is running and so retards the motor when it goes over so many rpms?

Hi

Thank you for the response

Yes that is correct

Wayne

My goal is to give you the best experience possible! I hope I have earned a 5-star rating! Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave today. If you need more assistance, please use the reply box and let me know.

Wayne
Wayne, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 11,337
Experience: worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling
Verified
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Wayne
Wayne
Wayne, Journeyman
Category: Medium and Heavy Trucks
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11,337 Satisfied Customers
Experience: worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling

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