Technical Service Bulletins

Bumpy Downshift

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Bumpy Downshift

This bulletin applies to 2014 Chevy Impala vehicles equipped with the 6T70 automatic transmission. Some owners may complain about a coast-down “bump” felt with closed throttle during a 4-3 downshift.

A revised calibration is available to address this concern. Update the TCM (transmission control module) with the latest software available on TIS2WEB.

When using a Tech 2 or a multiple diagnostic interface for reprogramming, make sure that it is updated with the latest software version.

During programming, battery voltage must be maintained within the proper range of 12-15 volts. According to GM, use only the approved Midtronics PSC 550 battery maintainer or equivalent.

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