P0721 on the 2004 GMC Sierra
The bulletins listed name this code in NHTSA's summary, or are about the same components. A bulletin or a recall listed here may apply to the model year. None of it is a diagnosis.
Nobody has written a description of this code yet.
| 3155 | 2005-05-11. Service bulletin. NO SHIFT, SPEEDOMETER ERRATIC/INOPERATIVE, P0721 C0237 P0500 C0055. *TT |
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| 01493 | 2004-03-02. Service bulletin. ALLISON LCT1000 PRNDL FLASH AND/OR WILL NOT MOVE WITH P0721, P0731, P0732, P0733, P0734, P0743, P0746, P0747, P0776, P0777, P1720, P1721, P1723 AND P1724. *TT |
| 00574A | 2004-02-27. Service bulletin. ALLISON LCT1000 NO SHIFT, SPEEDOMETER ERRATIC/INOPERATIVE, DIAGNOSTIC TROUBLE CODES (DTCS) P0721, C0237 POSSIBLE ANTI-LOCK BRAKE SYSTEM (ABS) LAMP ON. SI BULLETIN 1408789. *TT |
3 on file from NHTSA, as of 2026-10-19. See them in the bulletin list. A bulletin lists model years: read the document for which vehicles it concerns.