Powertrain, generic (extended)

P20C1 Reductant Heater C Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Heater C's control circuit is interrupted. Where the third element sits again depends on the maker: GM's 2025 DEF tables make heater 3 a second tank heater and test it like the others (output off, 2 s, Type A); Deutz assigns C to the return line heater; FCA's EcoDiesel has a heater 3 of its own. Hino's 2018 bulletin for J05 cab-overs lists P20C1 as heater 3 of the heated DEF line, specified at 5.5 ohms ±1 at 20 °C and replaced as a complete line if out of range. On the 6.6 L LML in GM's 2014 tables the glow plug control module drives the DEF heaters and reports this fault after an active test that discharges its capacitor, about 3.4 s, Type B. The affected section stays frozen longer after a cold start, delaying dosing.

Likely causes

Heating circuit in the line or tank module open (resistance check at the connector)
Unplugged or corroded heater C connector
Glow plug control module fault where it drives the DEF heaters (GM LML)

Symptoms

  • Warning lamp mainly after cold soaks
  • DEF dosing delayed after a cold start
  • SCR warning and countdown if the fault persists

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–1,200
Time0.5–3 h

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

Parts involved

reductant line heater c

Related codes

P20C2P20C3P20C4P20B9P20BDP20C5P221E

References: static.nhtsa.gov, gsi.ext.gm.com, gsi.ext.gm.com, serdia.deutz.com.