Reductant Metering Unit Temperature Sensor Circuit Low
The P20AE code indicates that the powertrain control module (PCM) has detected a low voltage condition in 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 DEF injection into the exhaust stream. A low circuit voltage typically means the sensor signal is below the expected range, often due to a short to ground, 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 ground in the sensor circuit wiring
- Corroded or damaged connector at the sensor
- Open circuit in the sensor 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
- Possible DTCs related to DEF system
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Visually inspect the reductant metering unit temperature sensor and its connector for damage, corrosion, or loose pins.
Step 3: Measure the sensor resistance and compare to manufacturer specifications (typically 2-10 kΩ at room temperature).
Step 4: Check the sensor signal circuit for a short to ground using a multimeter (should have voltage with key on).
Step 5: If sensor and wiring are okay, test the PCM output to the sensor circuit; replace PCM if necessary.
04. Commonly Affected Makes
05. 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 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 to fix P20AE typically ranges from $50 to $150 for parts and labor, depending on whether the sensor or wiring needs replacement. Sensor replacement is usually straightforward.