Reductant Heater Control Circuit Open
The P20B9 code indicates an open circuit 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 warnings.
1. Most Common Causes
- Open or shorted wiring in the reductant heater circuit
- Faulty reductant heater element
- Blown fuse or relay for the heater circuit
- Corroded or damaged connector at the heater
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Possible DEF system warnings on dashboard
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P20B9 and check for related codes.
Step 2: Visually inspect the reductant heater connector and wiring for damage or corrosion.
Step 3: Measure resistance across the heater element; compare to manufacturer specs (typically 0.5-2 ohms).
Step 4: Check for voltage at the heater connector with the ignition on; should be battery voltage.
Step 5: Inspect and test the fuse and relay for the reductant heater circuit.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive short distances, but prolonged driving may cause reduced engine performance, increased emissions, and potential damage to the SCR system. It is recommended to address the issue promptly.
How much does it cost to fix?▼
The cost to fix P20B9 typically ranges from $150 to $400, including parts and labor. The reductant heater element itself costs $50-$150, and labor adds $100-$250 depending on the vehicle and shop rates.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.