Generic (OBD-II) interpretation in the TuningBot DTC database.
P · PowertrainEmissionsOBD2
What P21C2 means
P21C2
Reductant Heater Relay Control Circuit/Open
Generic · emissions
Data confidence65%
The control module detected an interruption (open circuit) in the Reductant Heater Relay Control circuit, so the expected electrical continuity was not present.
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
Powertrain: engine, transmission and driveline systems.
2
Generic SAE-standard code: same meaning on every make.
1C2
Specific fault index within the subsystem.
Frequently asked questions about P21C2
What does P21C2 mean?
Reductant Heater Relay Control Circuit/Open. The control module detected an interruption (open circuit) in the Reductant Heater Relay Control circuit, so the expected electrical continuity was not present.
Is P21C2 generic or manufacturer-specific?
P21C2 is a generic OBD-II code: it has the same meaning on every make and model that follows the SAE standard.
Can TuningBot remove P21C2 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.
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