Powertrain, generic (extended)

P20AE Reductant Metering Unit Temperature Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P20AE is stored when the signal of the metering unit temperature sensor falls below its valid band. If the sensor is an NTC thermistor, the common design, though no maker confirms it publicly for this part, a low voltage stands for a very high indicated temperature. Typical reasons are then a signal wire chafed through to ground, moisture or DEF crystals bridging the connector pins, or a shorted sensor element. No manufacturer reference names this exact code; CARB merely requires the input to be checked for out-of-range values. The control unit then usually discards the reading and may suspend dosing. The upper counterpart is P20AF, while unclear electrical faults go to P20AC.

Likely causes

Signal wire shorted to ground (chafing near tank or frame)
Water or DEF residue bridging the connector pins
Sensor element in the metering unit shorted

Symptoms

  • Warning lamp on immediately after key-on
  • Module temperature shown far too hot in live data
  • DEF dosing suspended, inducement countdown possible

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–1,800
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant metering unitreductant metering temp sensor

Related codes

P20ACP20ADP20AFP20B0P2044

References: law.cornell.edu, picoauto.com, static.nhtsa.gov.