P20C1Reductant Heater C Control Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Warning lamp mainly after cold soaks
- DEF dosing delayed after a cold start
- SCR warning and countdown if the fault persists
- Likely causes
- LikelyHeating circuit in the line or tank module open (resistance check at the connector)
- PossibleUnplugged or corroded heater C connector
- RareGlow plug control module fault where it drives the DEF heaters (GM LML)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.