What does code P21A8 mean?

Q: What does code P21A8 mean?

Reductant Level Sensor B Circuit. P21A8 indicates that the powertrain control module (PCM) has detected an electrical fault in the reductant level sensor B circuit, which is part of the diesel exhaust fluid (DEF) system on vehicles equipped with selective catalytic reduction (SCR). The PCM monitors the sensor's signal voltage and sets this code when the voltage falls outside the expected range for the current fluid level, indicating an open circuit, short to ground, or short to power.

DTC codes / P21xx · Fuel and air metering / P21A8

P21A8Reductant Level Sensor B Circuit

P21A8 indicates that the powertrain control module (PCM) has detected an electrical fault in the reductant level sensor B circuit, which is part of the diesel exhaust fluid (DEF) system on vehicles equipped with selective catalytic reduction (SCR). The PCM monitors the sensor's signal voltage and sets this code when the voltage falls outside the expected range for the current fluid level, indicating an open circuit, short to ground, or short to power.

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.