P21B1

Reductant Level Sensor C Circuit Intermittent/Erratic

Severity

⚠️ Medium

Can you drive?

Yes, but get it checked soon

Approx. repair cost

$28–89 (est.)

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

P21B0 P21B2 P20EE