What Does P20AF Mean?
The reductant metering unit temperature sensor is sending a voltage signal higher than the expected range. This typically indicates an open circuit, sensor failure, or loss of ground in the DEF temperature monitoring system.
Common Causes
35%
Open circuit or broken wire in sensor signal or ground circuit
30%
Failed reductant metering unit temperature sensor (internal open)
20%
Poor ground connection at sensor or ECM
10%
Disconnected or loose connector at temperature sensor
5%
ECM internal fault (rare)
Diagnostic Steps
1
Step 1: Verify sensor connector is properly seated and inspect for pushed-out pins or terminal damage
2
Step 2: Backprobe sensor connector with key on, engine off and measure voltage at sensor signal wire (should be around 5V reference)
3
Step 3: Check continuity of signal wire from sensor to ECM with sensor disconnected
4
Step 4: Verify ground circuit continuity and resistance (should be less than 1 ohm to battery negative)
5
Step 5: Replace temperature sensor if all circuits test within specifications
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The reductant metering unit temperature sensor is sending a voltage signal higher than the expected range. This typically indicates an open circuit, sensor failure, or loss of ground in the DEF temperature monitoring system.
The most common cause of P20AF (Reductant Metering Unit Temperature Sensor Circuit High) is: Open circuit or broken wire in sensor signal or ground circuit
Typical repair costs for P20AF range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may experience power reduction or enter limp mode. Continued operation may lead to DEF system freeze damage in cold climates or countdown to vehicle derate.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20AF 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.
