P20BCReductant Heater A Control Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P20BC means the heater A control circuit reads high: the wire or output has picked up battery voltage, so the element may run when it should be off or cannot be switched at all. GM's 2025 DEF tables spot this on heater 1 (tank heater 1) mostly in the off state, when the high-side voltage lies between roughly 2 and 4.3 V instead of near zero; Type A after a 2 s debounce. Ford's criterion is current below 3 A with more than 5 V at the output while the power stage is off. GM's 2014 tables for the 6.6 L LML, where the glow plug module drives the heaters, look for more than 3.5 V at the heater pin (Type B). On the Touareg CNRB, VW sets it above 2.20 A signal current. For 2025 Ram 2500–5500 with the 6.7 L Cummins, FCA names P20BC the suction line heater and fixes it with DCU software (08-076-26).
- What you may notice
- Check engine light and DEF system warning
- Heater may stay energized, risking overheating or a drained battery
- Reduced power or speed limit once the inducement starts
- Likely causes
- LikelyHeater A control wire shorted to a battery-voltage circuit
- PossibleDEF control unit software fault (FCA 08-076-26 for 2025 Cummins Ram)
- RareHeater output stage or relay stuck switched on
- 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.