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Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 3304
Experience:  ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, EPA 608/609 HVAC Certified, Steering/Suspension and ABS/Brakes Technician
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We have a 2007 GMC 5500 that we replaced isolation module,

Customer Question

we have a 2007 GMC 5500 that we replaced isolation module, batteries, and starter. after running and warmed up it wont start like the batteries are dead. truck has 28,500 miles on it.
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 1 year ago.

My name is ***** ***** I will assist you.

That is odd. Do you have any check engine codes in the vehicle? If the isolator is connected properly, it shouldn't have any affect on the starting. I'm presuming you hae a PTO setup on the truck with upfitter controls since you have the isolator? Make sure there is nothing on the system interfering.

LOOK HERE for the wiring diagram for that year and model in case you need it.

Recheck your wiring and make sure something didn't come loose on you since you did change the starter. Check the relays and fuses to also make sure the is no issue with them due to something that could ave occurred with the first start.

Also, if the engine gets cool, does it restart? If so, then there is something wrong wit hthe new starter. I've had several of them burn up on the first crank on these models. They are bad on burning out the solenoids. Check the starter when the key is turned and see if you have ignition power. Also test for power in and ground. I would rule that out first, ESPECIALLY if it a reman. Leece Neville has been using chinese parts on their reman starters and Delco has been making bad brushes lately.

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Customer: replied 1 year ago.
It does start okay cold. But not great.. And I forgot to mention that it did the same exact thing with all the old stuff on it like the isolator the batteries and the starter nothings different since I replaced them all. And the volt meter stays at 9 to 10 volts for at least two minutes before ramping up to 14v. I know they all do it, but it seems my other trucks with same motor and year only takes a second. Is something stuck on? Like glow plugs or a heater for fuel system? And yes it has PTO but we don't use it. It has electric/hydraulic lift for dump body.
I have it over to my mechanic but he can't get to it until Thursday

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