What does code P21C2 mean?

Q: What does code P21C2 mean?

Reductant Heater Relay Control Circuit/Open. P21C2 indicates that the powertrain control module (PCM) has detected an open circuit or abnormal condition in the control circuit for the reductant heater relay, which is part of the diesel exhaust fluid (DEF) system. The PCM monitors the relay control circuit for expected voltage changes when the heater is commanded on or off, and this code sets when the circuit does not respond as expected, often due to a wiring fault or failed relay.

DTC codes / P21xx · Fuel and air metering / P21C2

P21C2Reductant Heater Relay Control Circuit/Open

P21C2 indicates that the powertrain control module (PCM) has detected an open circuit or abnormal condition in the control circuit for the reductant heater relay, which is part of the diesel exhaust fluid (DEF) system. The PCM monitors the relay control circuit for expected voltage changes when the heater is commanded on or off, and this code sets when the circuit does not respond as expected, often due to a wiring fault or failed relay.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.