| Subject: | Hard or Harsh 1-2 Shift |
| Models: | 2004-2007 Buick Rainier |
| 2004-2007 Cadillac Escalade, Escalade ESV and EXT |
| 2004-2008 Chevrolet Avalanche, Colorado, Express, Suburban, Tahoe, Trailblazer |
| 2004-2005 Chevrolet Corvette |
| 2004-2007 Chevrolet Silverado Classic |
| 2007-2008 Chevrolet Silverado |
| 2004-2008 GMC Canyon, Envoy, Savanna, Sierra, Sierra Denali, Yukon, Yukon XL, Yukon XL Denali |
| 2004-2007 GMC Sierra Classic |
| Equipped with 4L60E/4L65E/4L70E (RPOs - M30/M32/M70) Automatic Transmission |
This PI was superseded to update model years. Please discard PIP3170F.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:
The 4L60E/4L65E/4L70E may exhibit a condition of a harsh 1-2 upshift. There are usually two different types of harsh 1-2 shift.
Note: Starting in 2006 and future, some calibrations have been revised to give the 1-2 shift adapts much greater capability. These adapts can greatly improve 1-2 upshift feel but need upshifts to work. Make sure the vehicle has at
least 100 miles of varied driving conditions before attempting to evaluate the 1-2 upshifts.
Recommendation/Instructions:
- The harsh shift occurs at light throttle only, is random and may be worse if the accelerator is released just before or as the 1-2 shift occurs. This is a characteristic of the transmission shift that cannot be changed.
- The harsh shift is consistent and always occurs under the same driving conditions. The following items have been found to most frequently cause this concern:
| • | Check for the presence of DTCs. Some DTCs cause maximum line pressure resulting in harsh shifts. |
| • | 1-2 accumulator valve (371) sticking in the bore due to chips, debris or bore finish. |
| • | 4-3 sequence valve (383) sticking in the bore due to chips, debris or bore finish. |
| • | 1-2 accumulator piston (56) cracked or damaged or seal (55) cut. |
Important: The 1-2 accumulator piston / spring assembly is transmission model specific and may make use of only an inner spring or may use both an inner and an outer spring. The most accurate and up to date source of information
on how the accumulator assembly is built is available from the GMSPO parts catalog.
It is important to also refer to SI for other possible causes of a harsh 1-2 shift, Document ID # 10224.
Please follow this diagnostic or repair 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.
