Reductant Heater Control Circuit Low
The P20BB code indicates that the powertrain control module (PCM) has detected a low voltage condition in the reductant heater control circuit. This heater is part of the selective catalytic reduction (SCR) system, which heats diesel exhaust fluid (DEF) to prevent freezing in cold temperatures. A low circuit voltage can be caused by a faulty heater element, damaged wiring, or a defective relay, leading to insufficient DEF heating and potential emissions issues.
01. Most Common Causes
- Faulty reductant heater element
- Open or shorted wiring in the heater circuit
- Blown fuse or defective relay
- Corroded or loose electrical connectors
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for related codes.
Step 2: Visually inspect the reductant heater wiring and connectors for damage or corrosion.
Step 3: Test the heater circuit voltage and resistance using a multimeter.
Step 4: Check the fuse and relay for the reductant heater system.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code, as it can lead to reduced engine performance, increased emissions, and potential damage to the SCR system. Short trips to a repair shop are acceptable.
How much does it cost to fix?▼
The cost to fix P20BB typically ranges from $50 to $150 for parts and labor, depending on the root cause. Replacing a heater element or relay may cost more if the part is expensive.