Some 2021 Silverado 1500 and Sierra 1500 trucks equipped with the 5.3L V8 (RPO L84) and 10L80 10-speed automatic transmission (RPO MQB), excluding models with RPO YK9, may have a shudder condition when coasting to a stop between 15—13 mph (24—21 km/h). (Fig. 10) The shudder may feel similar to driving over rumble strips on the pavement when the vehicle is coming to a stop.
Fig. 10
During diagnosis, the shudder condition will be easily duplicated every time the vehicle coasts at the affected speeds. The shudder may be due to the reduction in the number of cylinders firing during deceleration, which may lead to structure-borne noise, vibration and harshness (NVH) on some vehicles when coasting to a stop between 15—13 mph (24—21 km/h).
If the shudder condition at the affected speeds is confirmed, reprogram the Engine Control Module (ECM) with the latest calibration available. Do not replace any parts for this condition.
It will also be necessary to perform the Crankshaft Position Variation Learn procedure covered in the appropriate Service Information once the ECM has been updated. The crankshaft position sensor variation is used to calculate reference period errors caused by slight tolerance variations in the crankshaft and crankshaft positon sensor, which allows the ECM to accurately compensate for reference period variations and detect misfire events over a wider range of engine speed and load. If the Crankshaft Position Variation Learn procedure is not completed, the ECM calibration will not provide the desired results.
TIP: Always verify that the VIN displayed in the left-side drop-down menu in Techline Connect and the top-center window match the VIN plate of the vehicle to be programmed prior to using Service Programming System 2 (SPS2) for programming or reprogramming a module. (Fig. 11)
Fig. 11
Refer to Bulletin #21-NA-207 for additional information.
– Thanks to Bryan Salisbury
