What does code P21AC mean?

Q: What does code P21AC mean?

Reductant Level Sensor B Circuit Intermittent/Erratic. P21AC indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the reductant level sensor B circuit, which monitors the level of diesel exhaust fluid (DEF) in the storage tank. The PCM expects a stable voltage or resistance from the sensor, but the signal is jumping or dropping out unpredictably, preventing reliable level readings.

DTC codes / P21xx · Fuel and air metering / P21AC

P21ACReductant Level Sensor B Circuit Intermittent/Erratic

P21AC indicates that the powertrain control module (PCM) has detected an intermittent or erratic signal from the reductant level sensor B circuit, which monitors the level of diesel exhaust fluid (DEF) in the storage tank. The PCM expects a stable voltage or resistance from the sensor, but the signal is jumping or dropping out unpredictably, preventing reliable level readings.

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.