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TuningBot DTC Database · v4.37.15

P21AA Reductant Level Sensor B Circuit Low

Generic (OBD-II) interpretation in the TuningBot DTC database.

P · PowertrainEmissionsOBD2

What P21AA means

P21AA
Reductant Level Sensor B Circuit Low Generic · emissions Data confidence 65%

The control module detected that the signal in the Reductant Level Sensor B circuit stayed below the expected operating range.

Symptoms

  • MIL or SCR/AdBlue warning illuminated
  • Possible start-count-down or torque limitation on some applications

Possible causes

  • Reductant quality or level fault
  • Dosing valve or supply module fault
  • NOx sensor fault
  • Frozen or crystallized reductant lines
  • Wiring or connector fault

Recommended checks

  • Read NOx sensor values and dosing system status
  • Check reductant level and quality data
  • Inspect dosing valve, lines and heater operation
  • Check wiring and connectors of the SCR components
  • Check for OEM technical bulletins and software updates

Related and nearby codes

Related codes
P21A8P21A9P21ABP21AEP21AF
P21 range
P2100P2101P2102P2103P2104P2105P2106P2107P2108P2109P210AP210BP210CP210DP210EP2110P2111P2112

How to read P21AA

P

Powertrain: engine, transmission and driveline systems.

2

Generic SAE-standard code: same meaning on every make.

1AA

Specific fault index within the subsystem.

Frequently asked questions about P21AA

What does P21AA mean?

Reductant Level Sensor B Circuit Low. The control module detected that the signal in the Reductant Level Sensor B circuit stayed below the expected operating range.

Is P21AA generic or manufacturer-specific?

P21AA is a generic OBD-II code: it has the same meaning on every make and model that follows the SAE standard.

Can TuningBot remove P21AA at file level?

If the fault logic lives in the ECU calibration, yes: our DTC Removal file service disables the specific fault entry. Checksum correction is not included: it is a separate, optional service. Not sure whether your case qualifies? Request a free assessment and our engineers will check your ECU file.

Other file services

Stage 1/2/3 TuningDPF RemovalEGR RemovalAdBlue / SCR RemovalDTC RemovalIMMO OFFSpeed Limiter (Vmax)

Understand the system behind this code: SCR / AdBlue System

ECU tuningDyno-tested results by model and engine See the results →

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