Powertrain, generic (extended)

P2A3F Excessive Time to Enter Alternative Fuel Control

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

On a bi-fuel or gas-start vehicle the control unit only changes over to gas once preconditions are met, for example warm coolant, enough pressure in the rail and a selected gas mode. P2A3F means this changeover did not happen within the calibrated time. GM's 2015 Impala bi-fuel bulletin PI1330 gives an idea of the conditions: below −20 °C ambient the engine starts on petrol and moves to CNG only when coolant reaches 50 °C. Ford's 2003 bi-fuel CNG pickups need at least 517 kPa rail pressure for a gas start and drop back to petrol below it. CARB treats the gas mode of such cars like a petrol engine up to model year 2018 and already demands a closed-loop entry time check (P0125 family). No maker documents P2A3F. Suspects are a slow thermostat, low tank pressure or a sticking valve.

Likely causes

Coolant warms up too slowly (thermostat stuck open, temperature sensor wrong)
Tank pressure too low for the switch-over
Regulator or vaporizer not heated enough by engine coolant
Tank or rail solenoid opening late or not at all

Symptoms

  • Vehicle keeps running on petrol much longer than usual
  • Gas indicator stays off or flashes
  • Check engine light, depending on calibration

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–800
Time0.5–3 h

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

Parts involved

afcmalt fuel tankalt fuel vaporizer

Related codes

P2A3EP0125P01A8P019F

References: law.cornell.edu, static.nhtsa.gov, static.nhtsa.gov.