Reductant Metering Unit Temp Sensor Circuit Intermittent/Erratic
The P20B0 code indicates an intermittent or erratic signal from the reductant metering unit temperature sensor circuit. This sensor monitors the temperature of the diesel exhaust fluid (DEF) in the metering unit, which is critical for proper injection into the exhaust stream. An erratic signal can cause the DEF injection system to malfunction, leading to increased NOx emissions and potential triggering of the check engine light. Common causes include wiring issues, connector corrosion, sensor failure, or problems with the DEF heater circuit.
1. Most Common Causes
- Faulty reductant metering unit temperature sensor
- Damaged or corroded wiring/connectors in the sensor circuit
- Intermittent open or short in the sensor circuit
- DEF heater circuit malfunction affecting sensor readings
- Powertrain control module (PCM) software or hardware issue
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or power
- Increased diesel exhaust fluid (DEF) consumption
- Failed emissions test due to high NOx levels
- Possible regeneration issues or DPF clogging
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data to identify related issues.
Step 2: Visually inspect the reductant metering unit temperature sensor and its wiring/connectors for damage, corrosion, or loose connections.
Step 3: Use a multimeter to test sensor resistance and compare to manufacturer specifications; check for continuity in the circuit.
Step 4: If wiring and sensor are okay, test the DEF heater circuit and PCM output signals to the sensor.
Step 5: If all else fails, replace the reductant metering unit temperature sensor and clear the code; test drive to verify repair.
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 increased emissions, reduced fuel economy, and potential damage to the DEF system or DPF. The vehicle may enter limp mode to protect the engine.
How much does it cost to fix?▼
The cost to diagnose and repair P20B0 typically ranges from $50 to $150 for parts and labor, depending on the root cause. Sensor replacement is usually under $100, while wiring repairs may be more.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.