Powertrain, generic (extended)

P20AF Reductant Metering Unit Temperature Sensor Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P20AF means the metering unit temperature signal has risen above its permitted band. For an NTC thermistor, the likely design though not publicly confirmed for this part, that looks like an extremely cold module. Electrically it is usually an open signal or ground wire, a terminal backed out of the connector or a short to a voltage source. Corrosion deserves attention: Hino's bulletins SB-16-015 and SB-16-016 explain that frozen DEF can damage the pump and let fluid creep into the pump connector and SCR harness; Hino names its own P142A there, not P20AF. Believing the module frozen, the control unit holds back dosing and may keep heating. No maker publishes P20AF itself.

Likely causes

Open signal or ground wire to the temperature sensor
DEF intrusion and corrosion in the pump connector or harness
Sensor element in the metering unit open
Signal wire shorted to a supply voltage

Symptoms

  • Module temperature shown far below ambient in live data
  • DEF warning and delayed or missing dosing
  • Further SCR codes if the harness is corroded

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–2,000
Time0.5–4 h

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

Parts involved

reductant metering unitreductant metering temp sensor

Related codes

P20ACP20ADP20AEP20B0P2045

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