There may be a whine sound heard under light acceleration or when coasting on some 2023-2024 Colorado and Canyon models equipped with the 8L45 or 8L80 8-speed automatic transmission (RPO N8R, MFC). The sound, usually heard around 25-50 mph (40-80 km/h), may be caused by cable isolation in 4th and 5th gear at approximately 42 mph (68 km/h) under moderate acceleration.
To help verify the source of the sound, follow the service procedure outlined in Bulletin #24-NA-002. The procedure covers driving the vehicle in 4th gear, at approximately 2000-2800 rpm, and observing if a gear whine sound is heard under light throttle or coasting. (Fig. 12) The intensity of the whine sound should change along with changes in the throttle position.
Fig. 12
Once the noise is noticed, vehicle speed should be increased to shift the transmission to 5th gear. A similar noise should still be audible in the 2000-2800 engine rpm range while in 5th gear.
During the test drive, there should not be any gear whine sound with the transmission in gears 1-2 or 6-8, or at engine speeds greater than 2800 rpm.
Once the sound has been verified under these conditions, install a transmission cable weight to help eliminate cable isolation and the gear whine sound while under moderate acceleration in 4th and 5th gear. (Fig. 13)
Fig. 13
For additional details, including parts information, refer to Bulletin #24-NA-002.
– Thanks to Marty Leach
