What Does P20AD Mean?
The temperature sensor signal from the reductant metering unit is reading outside expected parameters or not responding appropriately to temperature changes. The sensor may be providing inaccurate data that doesn't correlate with other system temperatures.
Common Causes
35%
Faulty temperature sensor providing inaccurate readings due to internal degradation
25%
Poor thermal contact between sensor and DEF metering unit causing lag or incorrect readings
20%
Intermittent wiring connection causing erratic or unstable sensor readings
15%
Contamination or crystallized DEF on sensor element affecting thermal transfer
5%
Incorrect sensor calibration or ECM software issue causing rationality failure
Diagnostic Steps
1
Step 1: Monitor DEF temperature sensor reading with scan tool and compare to ambient temperature and coolant temperature; verify logical correlation
2
Step 2: Allow vehicle to cold soak, then monitor sensor during warm-up cycle; verify smooth and appropriate temperature rise
3
Step 3: Remove sensor and inspect for DEF crystallization, damage, or poor mounting; clean and reinstall with proper thermal contact
4
Step 4: Test sensor resistance at various temperatures using heat gun or ice bath; compare readings to manufacturer specifications
5
Step 5: Check for intermittent connections by wiggling wiring harness while monitoring live sensor data for dropouts or spikes
Estimated Repair Cost
$150 - $550
Parts + labor, varies by vehicle and location
The temperature sensor signal from the reductant metering unit is reading outside expected parameters or not responding appropriately to temperature changes. The sensor may be providing inaccurate data that doesn't correlate with other system temperatures.
The most common cause of P20AD (Reductant Metering Unit Temperature Sensor Circuit Range/Performance) is: Faulty temperature sensor providing inaccurate readings due to internal degradation
Typical repair costs for P20AD range from $150 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Inaccurate temperature readings can cause improper DEF dosing or failure to protect system from freezing. Vehicle may enter reduced power mode or experience starting issues.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20AD to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Exhaust Fluid (DEF) Injection System / Selective Catalytic Reduction (SCR)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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