What does code P21AA mean?

Q: What does code P21AA mean?

Reductant Level Sensor B Circuit Low. P21AA indicates that the powertrain control module has detected a low voltage condition on the reductant level sensor B circuit, which typically monitors the diesel exhaust fluid level in a second tank or a specific section of the tank. The sensor's signal voltage has fallen below the expected range for the current operating conditions, which can prevent the system from accurately measuring the reductant level and may trigger warnings or inducement strategies.

DTC codes / P21xx · Fuel and air metering / P21AA

P21AAReductant Level Sensor B Circuit Low

P21AA indicates that the powertrain control module has detected a low voltage condition on the reductant level sensor B circuit, which typically monitors the diesel exhaust fluid level in a second tank or a specific section of the tank. The sensor's signal voltage has fallen below the expected range for the current operating conditions, which can prevent the system from accurately measuring the reductant level and may trigger warnings or inducement strategies.

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.