Reductant Metering Unit Temperature Sensor Circuit High
The P20AF code indicates that the reductant metering unit temperature sensor circuit is reading a voltage higher than expected. This sensor monitors the temperature of the diesel exhaust fluid (DEF) in the metering unit, which is crucial for proper injection into the exhaust stream. A high circuit condition typically means there is an open circuit, short to voltage, or a faulty sensor, leading to incorrect temperature readings and potential emissions system issues.
1. Most Common Causes
- Faulty reductant metering unit temperature sensor
- Open or shorted wiring in the sensor circuit
- Corroded or damaged connector
- Faulty reductant metering unit (internal failure)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
3. 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: Measure the sensor resistance and compare to manufacturer specifications.
Step 4: Check for voltage at the sensor connector; if voltage is present with key on, suspect a short to power.
Step 5: If wiring and sensor are okay, test the reductant metering unit for internal faults.
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 reduced performance, increased emissions, and potential damage to the selective catalytic reduction (SCR) system. Limp mode may activate, limiting vehicle speed.
How much does it cost to fix?▼
The cost to fix P20AF typically ranges from $50 to $150 for parts and labor, depending on whether the sensor or wiring needs replacement. If the reductant metering unit itself is faulty, costs can be higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.