Reductant Metering Unit Temperature Sensor Circuit Malfunction
The P20AC code indicates a problem with the reductant metering unit temperature sensor circuit, which is part of the Selective Catalytic Reduction (SCR) system. This sensor monitors the temperature of the diesel exhaust fluid (DEF) as it is injected into the exhaust stream. The Powertrain Control Module (PCM) detects an abnormal voltage or resistance in the sensor circuit, often due to a faulty sensor, wiring issues, or a short circuit. This can lead to improper DEF injection, affecting emissions control and potentially triggering the check engine light.
1. Most Common Causes
- Faulty reductant metering unit temperature sensor
- Open or shorted wiring in the sensor circuit
- Corroded or damaged connector
- Failed PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased emissions
- Possible DEF system warning message
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for related codes.
Step 2: Visually inspect the sensor and wiring for damage, corrosion, or loose connections.
Step 3: Test the sensor resistance and compare to manufacturer specifications.
Step 4: Check the voltage and ground at the sensor connector with a multimeter.
Step 5: If wiring and sensor are good, test the PCM output to the sensor circuit.
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 engine performance, increased emissions, and potential damage to the SCR system. Limp mode may activate, limiting speed and drivability.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether the sensor or wiring needs replacement. Diagnostic fees may add $50-$100.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.