Powertrain, generic (extended)

P20AC Reductant Metering Unit Temperature Sensor Circuit

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P20AC is the general circuit code for the temperature sensor built into the reductant metering unit, meaning the DEF supply or dosing module that pressurises the fluid. The control unit typically relies on this value to judge whether the module has thawed and may start pumping. The code stands for an electrical fault the software cannot assign to a low or high signal; those cases carry their own numbers, P20AE and P20AF. No manufacturer documents P20AC publicly. Hino, for example, files faults of its DEF pump temperature sensor under the maker-specific P142A instead. CARB requires such inputs to be watched continuously for circuit continuity. Drivers see a DEF or engine warning and, if it is ignored, speed or restart limits.

Likely causes

Corroded or loose connector at the DEF supply/metering module
Damaged sensor wiring between module and control unit
Temperature sensor inside the metering unit failed (usually replaced with the module)
Input fault in the dosing or engine control unit

Symptoms

  • Malfunction indicator or DEF/SCR warning lamp on
  • Dosing delayed or stopped in cold weather
  • Inducement countdown with speed or restart limit

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

P20ADP20AEP20AFP20B0P2042P205B

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