What Does P20AE Mean?
The temperature sensor in the diesel exhaust fluid (DEF) metering unit is reporting a voltage signal below the expected threshold. This indicates a potential short to ground, sensor failure, or wiring issue in the reductant system temperature monitoring circuit.
Common Causes
35%
Damaged or shorted wiring harness between temperature sensor and ECM
30%
Failed reductant metering unit temperature sensor
20%
Corroded or damaged connector terminals at sensor or ECM
10%
Short circuit to ground in sensor wiring
5%
Failed engine control module (rare)
Diagnostic Steps
1
Step 1: Visually inspect the DEF metering unit temperature sensor connector for corrosion, damage, or moisture intrusion
2
Step 2: Check wiring harness from sensor to ECM for chafing, pinching, or damage, especially near exhaust components
3
Step 3: Disconnect sensor and measure resistance across sensor terminals; compare to specifications (typically 2-3k ohms at 68°F)
4
Step 4: Perform voltage drop test on sensor ground circuit to verify integrity
5
Step 5: If wiring and grounds test good, replace temperature sensor and retest system
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The temperature sensor in the diesel exhaust fluid (DEF) metering unit is reporting a voltage signal below the expected threshold. This indicates a potential short to ground, sensor failure, or wiring issue in the reductant system temperature monitoring circuit.
The most common cause of P20AE (Reductant Metering Unit Temperature Sensor Circuit Low) is: Damaged or shorted wiring harness between temperature sensor and ECM
Typical repair costs for P20AE range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may enter reduced power mode (limp mode) to protect emissions system. Extended driving with fault may result in vehicle derate or no-start condition after restart.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20AE to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Emissions Control System (SCR)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
