04-05 Colorado and Canyon - 3-2 and 4-2 WOT Down Shift Information - kw 2.8 3.5 4L60E accelerate automatic down downshift engine hard no open throttle transmission wide

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Some customers may comment that their Colorado or Canyon Truck with an automatic transmission does not downshift to 2nd gear during hard acceleration at highway speeds.

This may be a normal condition. The PCM is calibrated with a maximum speed value that a 2nd gear downshift can occur up to. If the vehicle speed exceeds this calibrated value, the PCM will prevent a 2nd gear downshift from occurring. To determine this calibrated value, compare the Model Year, Axle Ratio RPO and Tire Size RPO of the truck to the list below. These are approximate speeds and may vary slightly from vehicle to vehicle. If a 2nd gear downshift does not occur above the calibrated value from the chart below, no repairs should be performed since the vehicle is operating as designed. Note: It is not possible to install 2005 PCM calibrations into a 2004 truck or vice versus.

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2004 Models with RPO GT4 (3.73 Axle Ratio) and Tire RPO YWU = 73 MPH

2004 Models with RPO GU6 (3.42 Axle Ratio) and Tire RPO YWU, YFL, YET, YKU, YCE or YGR = 73 MPH

2004 Models with RPO GU6 (3.42 Axle Ratio) and Tire RPO YGR = 66 MPH

2004 Models with RPO GT4 (3.73 Axle Ratio) and Tire RPO YFL, YET, YKU or YCE = 66 MPH

2004 Models with RPO GT5 (4.10 Axle Ratio) and Tire RPO YWU = 66 MPH

2004 Models with RPO GT4 (3.73 Axle Ratio) and Tire RPO YGR = 59 MPH

2004 Models with RPO GT5 (4.10 Axle Ratio) and Tire RPO YFL = 59 MPH

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2005 Models with RPO GT4 (3.73 Axle Ratio) and Tire RPO YWU = 81 MPH

2005 Models with RPO GU6 (3.42 Axle Ratio) and Tire RPO YWU, YFL, YET, YKU, YCE or YGR = 81 MPH

2005 Models with RPO GU6 (3.42 Axle Ratio) and Tire RPO YGR = 73 MPH

2005 Models with RPO GT4 (3.73 Axle Ratio) and Tire RPO YFL, YET, YKU or YCE = 73 MPH

2005 Models with RPO GT5 (4.10 Axle Ratio) and Tire RPO YWU = 73 MPH

2005 Models with RPO GT4 (3.73 Axle Ratio) and Tire RPO YGR = 65 MPH

2005 Models with RPO GT5 (4.10 Axle Ratio) and Tire RPO YFL = 65 MPH

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Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

(04 05 Chevrolet Colorado with an Automatic Transmission) and (04 05 GMC Canyon with an Automatic Transmission)

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