Reductant Metering Unit Heater Control Circuit Performance
The P20B6 code indicates 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 warming the diesel exhaust fluid (DEF) to prevent freezing and ensure proper injection. When the circuit performance is out of range, the PCM detects a malfunction, often due to electrical faults or heater element failure.
01. Most Common Causes
- Faulty reductant metering unit heater
- Open or shorted heater circuit wiring
- Corroded or damaged electrical connectors
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased emissions
- Possible DEF system warnings
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect the heater connector and wiring for damage or corrosion.
Step 3: Measure resistance of the heater element (typically 2-10 ohms).
Step 4: Check for voltage and ground at the heater connector with the ignition on.
Step 5: If wiring and heater are okay, test the PCM output or replace the metering unit.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can lead to reduced engine performance, increased emissions, and potential damage to the SCR system. Limp mode may activate.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on whether the heater unit or wiring needs replacement. Labor is usually 1-2 hours.