Reductant Heater Control Circuit/Open
The P20B9 code indicates a problem in the reductant heater control circuit, which is part of the Selective Catalytic Reduction (SCR) system. This heater warms the diesel exhaust fluid (DEF) to prevent freezing and ensure proper injection. An open circuit means there is a break in the electrical path, preventing the heater from functioning. This can lead to reduced NOx conversion efficiency and potential emissions system issues.
01. Most Common Causes
- Faulty reductant heater element
- Open or shorted wiring in the heater circuit
- Blown fuse or relay for the heater
- Failed reductant heater control module
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or power
- Increased exhaust emissions
- Possible DEF system warning messages
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the reductant heater wiring and connector for damage or corrosion.
Step 3: Test the heater circuit resistance with a multimeter; compare to manufacturer specs.
Step 4: Check the fuse and relay for the reductant heater; replace if blown.
Step 5: If wiring and fuses are good, test the heater element itself; replace if open.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
Driving short distances may be possible, but continued operation can lead to reduced emissions control and potential damage to the SCR system. It's best to address the issue promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether it's a simple fuse replacement or a heater element repair.