P20BAReductant Heater A 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
- P20BA is the plausibility test for heater A: the circuit is intact, yet the current, resistance or power the element takes does not match the command. GM's 2025 DEF tables compute the resistance of heater 1, the tank heater, and fail it below 1.00 or above 1.80 ohms, or when power strays more than 45 W from the request, after 8 s as Type A; the 2018 tables use a 1.05–1.93 ohm window. Ford checks circuit 1, also the tank heater, a single time each trip while it runs at full power: under 3 A and under 5 V at the output while switched on, or the reverse when off. FCA reflashed 2014 Ram 1500 EcoDiesel engines that logged P20BA without a real fault (18-028-14). Volvo and Mack advise diagnosing it like the pressure-build failure P20E8, including lines, filters and the coolant heating valve.
- What you may notice
- Malfunction indicator lamp with DEF system message
- DEF tank stays cold or frozen in winter although the engine is warm
- Possible speed limitation after the inducement countdown
- Likely causes
- LikelyAged heater element whose resistance has drifted out of the allowed window
- PossibleCorroded or loose heater terminals adding resistance under load
- PossibleControl software setting the code without a defect (FCA 18-028-14 reflash)
- RareDEF pump unable to build pressure because of swapped or blocked lines (Volvo/Mack KC-4)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €100 – €1,800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.