P20C2Reductant Heater C Control Circuit Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P20C2 says heater C is connected but does not take the power the control unit expects. In GM's 2025 tables heater 3, the second tank heater, must measure between 1.50 and 2.60 ohms and stay within 29 W of its command; otherwise Type A after 8 s. Ford reads the code differently on its diesels: there it means the heater supply voltage has dropped below 5 V, tested a single time per trip with the heaters at full load and again within the glow plug module diagnostics, so a weak feed or relay is the first suspect. FCA titles it Reductant Heater 3 Control Circuit Performance on the 3.0 L EcoDiesel and issued several PCM reflashes against false entries, among them 18-028-14 and 18-019-15. Deutz lists it for the return line heater as over-temperature. The usual result is late dosing in frost.
- What you may notice
- Check engine light after a heating cycle
- DEF thaws slowly in cold weather
- Further heater codes if the common supply is weak
- Likely causes
- LikelyHeater supply below 5 V because of a weak relay, fuse or feed wire (Ford)
- PossibleEngine control software setting the code falsely (FCA 18-028-14, 18-019-15)
- PossibleHeater C element resistance outside its window
- 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: €0 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.