P21AC

Reductant Level Sensor B Circuit Intermittent/Erratic

Severity

⚠️ Medium

Can you drive?

Limited driving only, diagnose soon

Approx. repair cost

$28–89 (est.)

Symptoms

Check Engine Light Is On
Reduced engine power
Low reagent message on instrument panel
Unstable AdBlue level readings
Possible transition to emergency mode

Causes

Poor contact in the sensor connector
Open or shorted wiring harness
Reagent level sensor malfunction
Problems with the SCR control unit
Corrosion of contacts due to reagent ingress

How to Fix

Check the connections and connectors of the sensor
Test the sensor circuit for open and short circuits
Check sensor resistance to specifications
Replace the reagent level sensor if necessary
Clear error codes and test drive

Related codes

P21A9 P21AA P21AD