P1621: owner reports and bulletins

Powertrain (manufacturer-specific). We haven't written the explanation for this code yet. Below is what owners and manufacturers have filed with NHTSA.

Got P1621 on your scanner? Tell the mechanic your year, make, model and any symptoms and you'll get the likely cause and what to check first. Ask about this code.

What owners report to NHTSA

No consumer complaints filed with NHTSA mention P1621. That usually means it's rare, or owners don't quote the code when they file.

Manufacturer service bulletins that name P1621

25 technical service bulletins and manufacturer communications filed with NHTSA mention P1621, from 10 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:

  • CHRYSLER 300 (2013, 2014, 2015), bulletin 10180287: Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. …
  • DODGE CHALLENGER (2013, 2014, 2015), bulletin 10180287: Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. …
  • DODGE CHARGER (2013, 2014, 2015), bulletin 10221897: Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. …
  • GMC ENVOY (2007, 2008, 2009, 2010), bulletin 10113571: This informational bulletin communicates Information to technicians on control module Diagnostic Trouble Code(s) (DTC)(s) P0601, P0602, P0603, P0604, P0606, P062F, P06F3, P1621 which can be shared in multiple modules.
  • BUICK ENCLAVE (2008, 2009, 2010, 2011), bulletin 10113571: This informational bulletin communicates Information to technicians on control module Diagnostic Trouble Code(s) (DTC)(s) P0601, P0602, P0603, P0604, P0606, P062F, P06F3, P1621 which can be shared in multiple modules.
  • CADILLAC ATS (2013, 2014, 2015, 2007), bulletin 10113571: This informational bulletin communicates Information to technicians on control module Diagnostic Trouble Code(s) (DTC)(s) P0601, P0602, P0603, P0604, P0606, P062F, P06F3, P1621 which can be shared in multiple modules.

Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.