GM hybrid bump/jerk

This bulletin applies to a number of GM hybrid vehicles, including 2009-2011 Cadillac Escalade, GMC Sierra and Chevy Silverado, and 2008-2011 Chevy Tahoe and GMC Yukon, all with two-mode Hybrid option RPO HP2 and 2ML70 transmission RPO M99.

Customers may comment on either of two drivability concerns. Bumps, jerks and/or surges caused by the auxiliary pump which occur during a transition into, out of, or during an Auto Stop, as observed on the tachometer.

A lull (clutch slipping) followed by a kick (clutch grabbing) during acceleration while in Auto Stop or during a transition to Engine On. This condition typically occurs just before and engine restart is observed on the tachometer.Surge or lunge during deceleration below 25 mph with light to moderate braking. This typically occurs after the tachometer drops below idle speed to anter an Auto Stop. These concerns may be caused by an auxiliary transmission fluid pump concern or a slipping clutch within the transmission.

NOTE: There may also be audible indications of electric motor speed increases and clicking noises associated with the auxiliary transmission fluid pump stall.

This concern is often accompanied by DTCs P2797, P0C2B and/or P079A. However, due to the intermittent nature of such complaints, there may be no DTCs set and reproducing the complaint can be difficult.

1. Check all vehicle modules and address any DTCs that may be present except for P2797 or P0C2B.

2. Once other DTCs have been addressed, obtain the date code of the auxillairy transmission fluid pump control module (this is found on the side of the module opposite the fluid hoses).

3. Follow the standard P2797 and/or P0C2B diagnostic procedures in order to diagnose the root cause of the complaint.

4,If the P2797 and/or P0C2B procedures do not identify either the auxiliary transmission fluid pump control module or auxiliary transmission fluid pump fault and the complaint is re-produced during those test procedures, inspect the :Hybrid Low, 1-2 clutch” assembly. Concerns relating to the “Hybrid Low, 1-2 clutch” assembly, typically manifest as a P079A DTC, but may not set the DTC.

5. If the concern does not re-produce, the “Hybrid Low, 1-2 clutch” assembly is operating normally and the control module has a Date Code of 089-11-XXXX or older, replace the auxiliary transmission fluid pump control module.

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