Reductant Metering Unit Temperature Sensor Circuit High
The P20AF code indicates that the powertrain control module (PCM) has detected a high voltage signal from the reductant metering unit temperature sensor circuit. This sensor monitors the temperature of the diesel exhaust fluid (DEF) metering unit, which is critical for proper DEF injection into the exhaust stream. A high circuit condition typically means the sensor signal is above the expected range, often due to a short to voltage, a faulty sensor, or wiring issues. This can lead to incorrect DEF dosing, potentially causing increased emissions and triggering the check engine light.
01. Most Common Causes
- Faulty reductant metering unit temperature sensor
- Short to voltage in the sensor circuit wiring
- Corroded or damaged connector at the sensor
- Open circuit in the sensor ground or signal wire
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check engine light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve the code and freeze frame data.
Step 2: Visually inspect the sensor and wiring for damage, corrosion, or loose connections.
Step 3: Test the sensor's resistance and voltage output with a multimeter and compare to manufacturer specs.
Step 4: Check for shorts to power or ground in the circuit by disconnecting the sensor and testing the harness.
Step 5: If all checks pass, replace the reductant metering unit temperature sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally not recommended to drive long distances with this code, as it can cause incorrect DEF dosing, leading to increased emissions and potential damage to the SCR system. The vehicle may enter limp mode, reducing power.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for the sensor part, plus labor if done by a shop. DIY replacement can save on labor costs.