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TuningBot DTC Database · v4.37.15

P21CB Reductant Control Module Supply Voltage Low

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

P · PowertrainEmissionsOBD2

What P21CB means

P21CB
Reductant Control Module Supply Voltage Low Generic · emissions Data confidence 65%

The control module detected that the Reductant Control Module Supply voltage stayed below the expected 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

P21 range
P2100P2101P2102P2103P2104P2105P2106P2107P2108P2109P210AP210BP210CP210DP210EP2110P2111P2112

How to read P21CB

P

Powertrain: engine, transmission and driveline systems.

2

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

1CB

Specific fault index within the subsystem.

Frequently asked questions about P21CB

What does P21CB mean?

Reductant Control Module Supply Voltage Low. The control module detected that the Reductant Control Module Supply voltage stayed below the expected range.

Is P21CB generic or manufacturer-specific?

P21CB is a generic OBD-II code: it has the same meaning on every make and model that follows the SAE standard.

Can TuningBot remove P21CB 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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