What does code P21B1 mean?

Q: What does code P21B1 mean?

Reductant Level Sensor C Circuit Intermittent/Erratic. P21B1 indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the reductant level sensor C circuit, which monitors the level of diesel exhaust fluid (DEF) in the tank. The PCM expects a steady voltage or resistance from the sensor, but the signal drops out or jumps erratically, setting this code.

DTC codes / P21xx · Fuel and air metering / P21B1

P21B1Reductant Level Sensor C Circuit Intermittent/Erratic

P21B1 indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the reductant level sensor C circuit, which monitors the level of diesel exhaust fluid (DEF) in the tank. The PCM expects a steady voltage or resistance from the sensor, but the signal drops out or jumps erratically, setting this code.

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.