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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20AD
P20AD indicates the powertrain control module has detected an out-of-range or erratic signal from the temperature sensor built into the diesel exhaust fluid (DEF) metering unit. The computer compares this sensor's reading against expected values after a cold start and during normal dosing, and it flags the circuit when the voltage or calculated temperature falls outside the calibrated window for a set time.
Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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