Reductant Metering Unit Heater Control Circuit/Open
The P20B5 code indicates an open or malfunction in the heater control circuit of the reductant metering unit, which is part of the selective catalytic reduction (SCR) system. This heater is essential for preventing diesel exhaust fluid (DEF) from freezing in cold temperatures. When the circuit is open, the heater cannot operate, leading to potential DEF freezing and increased emissions.
1. Most Common Causes
- Open or shorted wiring in the heater circuit
- Faulty reductant metering unit heater
- Corroded or damaged electrical connector
- Blown fuse related to the heater circuit
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 an OBD2 scanner to confirm the P20B5 code and check for related codes.
Step 2: Visually inspect the wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the heater circuit for continuity and resistance using a multimeter.
Step 4: Check the fuse for the reductant metering unit heater and replace if blown.
Step 5: If wiring and fuse are okay, test the heater element itself; replace if faulty.
4. 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 DEF freezing and potential damage to the SCR system. In some cases, the vehicle may enter limp mode, reducing speed and performance.
How much does it cost to fix?▼
The cost to fix P20B5 typically ranges from $50 to $150 for parts and labor, depending on whether it's a simple wiring repair or a heater replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.