What does code P21DD mean?

Q: What does code P21DD mean?

Reductant Heater A Current Too Low. P21DD means the engine computer has commanded the reductant heater circuit on and the current flowing through it is lower than expected, indicating an open circuit, high resistance, or a failed heater element. The reductant heater warms the diesel exhaust fluid (DEF) so it can be injected into the exhaust for selective catalytic reduction (SCR), and without adequate current the fluid can freeze or the system cannot regulate temperature properly.

DTC codes / P21xx · Fuel and air metering / P21DD

P21DDReductant Heater A Current Too Low

P21DD means the engine computer has commanded the reductant heater circuit on and the current flowing through it is lower than expected, indicating an open circuit, high resistance, or a failed heater element. The reductant heater warms the diesel exhaust fluid (DEF) so it can be injected into the exhaust for selective catalytic reduction (SCR), and without adequate current the fluid can freeze or the system cannot regulate temperature properly.

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.