Service bulletins for the 2021 Chevrolet 4500HD
A bulletin is a manufacturer's communication to its dealers, as NHTSA indexes it. The summary is NHTSA's. The document is the manufacturer's: read it at NHTSA. A bulletin is not a recall, and listing a model year does not mean every vehicle of it is concerned.
318 on file from NHTSA, as of 2026-10-19.
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Only bulletins with component: Automatic transmission are shown. Show all
| 17-NA-066 | 2023-07-25. Service bulletin. POWER TRAIN:AUTOMATIC TRANSMISSION; POWER TRAIN. This service bulletin provides information for automatic transmission Oil Cooler Flush and flow test. |
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| N222380840 | 2022-11-17. Service bulletin. POWER TRAIN:AUTOMATIC TRANSMISSION. General Motors has decided to conduct a Voluntary Emissions Recall on certain vehicles with a 6.6L engine (RPO L8T). The Transmission Control Module (TCM) in these vehicles may have been service reprogrammed with incorrect calibrations. If this occurred, the transmission shift quality and timing could be degraded. Dealers are to reprogram the TCM. |
| 990420002L | 2021-08-09. Service bulletin. POWER TRAIN:MANUAL TRANSMISSION; POWER TRAIN:AUTOMATIC TRANSMISSION; EQUIPMENT. This service bulletin provides information on Driveline Clunk Noise and what is acceptable and what is considered normal operation. |
The summaries are NHTSA's. Each bulletin's page links NHTSA's copy of the manufacturer's document.