Powertrain, generic (extended)

P20BA Reductant Heater A Control Circuit Performance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

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.

Likely causes

Aged heater element whose resistance has drifted out of the allowed window

Corroded or loose heater terminals adding resistance under load

Control software setting the code without a defect (FCA 18-028-14 reflash)

DEF pump unable to build pressure because of swapped or blocked lines (Volvo/Mack KC-4)

Symptoms

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

Repair estimate

DifficultyHardWorkshop job

Parts and labour€100–1,800

Time0.5–5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant line heater a

References: fordservicecontent.com, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.