P20BC code meaning
Reductant Heater A Control Circuit High
Powertrain system Generic code P20xx codes Check engine light
What P20BC means
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).
P20BC at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P20BC
- 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
Common causes of P20BC
- Most likelyHeater A control wire shorted to a battery-voltage circuit
- PossibleDEF control unit software fault (FCA 08-076-26 for 2025 Cummins Ram)
- Less likelyHeater output stage or relay stuck switched on
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant line heater a
What each part of P20BC means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| BC | The exact fault in that area. |
What to do next
- Note P20BC and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P20BC
What does P20BC mean?
P20BC means "Reductant Heater A Control Circuit High". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P20BC?
Drive gently and only to a workshop. With P20BC the car can go into limp mode (reduced power) to protect itself.
Will P20BC fail an emissions test?
Yes, it can. P20BC is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P20BC to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P20BC clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.