P21B1
Reductant Level Sensor C Circuit Intermittent/Erratic
P21B1 is an OBD-II diagnostic trouble code meaning: Reductant Level Sensor C Circuit Intermittent/Erratic. Common causes: reagent level sensor malfunction, oxidation or damage to sensor contacts. Estimated repair cost: $28–89.
Symptoms
- Check Engine Light Is On
- Low reagent level message when tank is full
- Reducing engine power (limp mode)
- Unstable AdBlue level readings
- Ammonia smell from the exhaust
Causes
- Reagent level sensor malfunction
- Oxidation or damage to sensor contacts
- Open or short circuit in the sensor circuit
- Poor quality or freezing of the reagent
- Problems with the SCR control unit
How to Fix
- Check the level and quality of AdBlue reagent
- Inspect the connector and wiring of the level sensor
- Test sensor resistance
- Check the sensor circuit for open circuit and short circuit
- If necessary, replace the reagent level sensor
Related codes
Error P21B1 by Vehicle Brand
FAQ
What does the P21B1 code mean?
P21B1 is an OBD-II diagnostic trouble code that indicates: Reductant Level Sensor C Circuit Intermittent/Erratic
What causes a P21B1 error code?
The most common causes of P21B1 include: Reagent level sensor malfunction; Oxidation or damage to sensor contacts; Open or short circuit in the sensor circuit; Poor quality or freezing of the reagent.
How do I fix a P21B1 diagnostic trouble code?
To fix P21B1: Check the level and quality of AdBlue reagent. Inspect the connector and wiring of the level sensor. Test sensor resistance. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P21B1?
Yes, but get it checked soon
How much does it cost to fix P21B1?
The estimated repair cost for P21B1 is $28–89. Actual cost depends on your vehicle, location, and labor rates.
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