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GM Bob
GM Bob, ASE Master Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 936
Experience:  30 plus years experience as GM technician, ASE Master Technician and GM Certified
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My gmc c4500 wont go over 25 mph, c4500 service truck 2007,

Customer Question

my gmc c4500 wont go over 25 mph
JA: What is the model/year of your GMC?
Customer: c4500 service truck 2007
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: new gas pedal, throttle body, checked wires, all good
JA: Has the vehicle turned into a gas hog? And how does it start -- same as usual?
Customer: starts fine not sure about gas hog
JA: Anything else you want the mechanic to know before I connect you?
Customer: no thats it.
Submitted: 17 days ago.
Category: Medium and Heavy Trucks
Expert:  GM Bob replied 16 days ago.

Hello my name is ***** ***** I can help.

Can you post your VIN number?

I need to ask is there a PTO switch on the dash? If so is it on this will reduce engine RPM?

I have seen this before

Please get back with me.

Thank you

Customer: replied 16 days ago.
VIN# ***** No Dump.
Expert:  GM Bob replied 16 days ago.

Even if it's not a dump there is a switch on the dash.

Expert:  GM Bob replied 16 days ago.

You have this build option


Customer: replied 16 days ago.
I don't know I will go and check. We let you know Thanks. I did some research sounds like truck is in limp mode.
Expert:  GM Bob replied 16 days ago.

If you have a scan tool look for any data that may show the PTO is ON

Customer: replied 16 days ago.
We did a scan check nothing came up.
Expert:  GM Bob replied 16 days ago.

I looked in service manual there are not showing any data for PTO.

Expert:  GM Bob replied 14 days ago.

Do you still need help?

Customer: replied 14 days ago.
Expert:  GM Bob replied 14 days ago.

When you say it won't go over 25 mph.

Is the trans shifting or is it stuck in a lower gear?

How high does the rpm go?

Do you have good power up to 25 mph?

I take it you didn't find a switch on the dash?

Customer: replied 14 days ago.
Rpm won't go over 2000, power is good no switch
Expert:  GM Bob replied 14 days ago.

Did this just happened all of a sudden?

Does your scan tool display throttle plate info and gas pedal info?

Customer: replied 14 days ago.
all of a sudden
Expert:  GM Bob replied 14 days ago.

Are you 100% there is no switch on the dash?

It maybe unmarked.

Can you post a picture of your dash panel?

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