Loss of power

John Technical Support Specialist New York Posted  
2006 GMC C4500 Topkick C4C042 6.6L (2 LLY)
Loss Of Power/Speedometer Not Reading Properly

2003 Through 2009 GMC topkick and Chevrolet Kodiak medium duty vehicles 

You may have a customer come in to your shop saying that there speedometer is reading wrong that it goes to 80 mph and the truck seems to have no power.

When programming the ecm if you do not program the tire size and gear ratio into the ecm this will happen. The tire rpm is 641rpm for 225/70/R19.5 and 622 rpm for 245/70/R19.5,

After you put in the axle ratio and tire size you must shut off the ignition for 2 min​.​to power down the ecm or it will not take the change.