P21C5

Symptoms

• Check Engine Light
• Low AdBlue level message (even with a full tank)
• Reduced engine power
• Increased fuel consumption
• Problems starting the engine (in some models)

Causes

• Crystallization of AdBlue in the sensor
• Mechanical jamming of the float
• Sensor contamination
• Malfunction of the level sensor itself
• Problems with wiring or connectors

How to Fix

1. Check AdBlue level and quality
2. Clean the level sensor from crystallized deposits
3. Check the electrical connections of the sensor
4. Replace the reagent level sensor if necessary
5. Reset the error and take a test drive

Related codes

Error P21C5 by Vehicle Brand