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P1DEF on the 2016 Toyota Mirai

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.

This code is specific to a manufacturer and is not described here. Its meaning is in the manufacturer's service information.

Bulletins for this model year that name P1DEF
TSB0046222022-09-15. Service bulletin. TSB: Some 2016 ? 2019 model year Mirai vehicles may exhibit a warning message, ?FC malfunction, return vehicle to dealer for service.? This message is accompanied by Diagnostic Trouble Code (DTC) P1DEF (450 FC Stack Performance). The Fuel Control Module (FCM) calibration has been revised to address this condition
T-SB-0318-17_Rev2019-10-15. Service bulletin. TSB: REVISION NOTICE September 20, 2019 Rev2: ? Applicability has been updated to include 2018 and 2019 model year Mirai vehicles. ? The Production Change Information, Parts Information, and Calibration sections have been updated. September 5, 2018 Rev1: ? The Parts Information section has been updated. Some 2016 ? 2019 model year Mirai vehicles may exhibit a warning message, "FC malfunction, return vehicle to dealer for service." This message is accompanied by Diagnostic Trouble Code (DTC) P1DEF (450 FC Stack Performance). The Fuel Control Module (FCM) calibration has been revised to address this condition.
T-SB-0318-17-Rev2018-12-03. Service bulletin. TSB: REVISION NOTICE September 5, 2018 Rev1: ? The Parts Information section has been updated. Any previous printed versions of this bulletin should be discarded. Some 2016 ? 2017 model year Mirai vehicles may exhibit a warning message, "FC malfunction, return vehicle to dealer for service." This message is accompanied by Diagnostic Trouble Code (DTC) P1DEF (450 FC Stack Performance). The Fuel Control Module (FCM) calibration has been revised to address this condition.
T-SB-0318-172018-04-23. Service bulletin. TSB: Some 2016 ? 2017 model year Mirai vehicles may exhibit a warning message, "FC malfunction, return vehicle to dealer for service." This message is accompanied by Diagnostic Trouble Code (DTC) P1DEF (450 FC Stack Performance). The Fuel Control Module (FCM) calibration has been revised to address this condition.

4 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.