Reductant Metering Unit Heater Control Circuit Performance
The P20B6 code indicates that the powertrain control module (PCM) has detected a performance issue in the heater control circuit of the reductant metering unit, which is part of the selective catalytic reduction (SCR) system. This heater is responsible for preventing the diesel exhaust fluid (DEF) from freezing in cold temperatures. A malfunction can cause the DEF to freeze, leading to increased emissions and potential damage to the SCR system.
1. Most Common Causes
- Faulty reductant metering unit heater
- Open or shorted heater circuit wiring
- Blown fuse or relay for the heater circuit
- Failed PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Possible DEF freezing in cold weather
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve freeze frame data and confirm the code.
Step 2: Visually inspect the heater wiring and connector for damage or corrosion.
Step 3: Test the heater resistance with a multimeter (typically 0.5-2 ohms).
Step 4: Check the fuse and relay for the heater circuit.
Step 5: If all else is fine, replace the reductant metering unit.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances, as the DEF may freeze in cold weather, causing increased emissions and potential damage to the SCR system. You may experience reduced power or limp mode.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, depending on whether the issue is a simple fuse replacement or a more complex heater unit replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.