Powertrain, generic (extended)

P2A57 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2A57 sets when the outlet sensor on vaporizer B pulls its signal below the lowest valid voltage. On a thermistor that loses resistance with heat, as in the Ford CNG rail sensor, this would mean extreme heat, so the realistic causes are a signal lead grounded against the chassis and an internally shorted sensor. Long harness runs, common when the gas parts sit far from the controller, add chafing points. A falsely hot value is risky because the system could believe B is ready while it is cold. TransEco, for its comparable rail sensor fault, substitutes the intake air reading on dedicated systems and forces petrol on bi-fuel ones. No maker lists P2A57. Unplug the sensor: the reading must swing to cold, otherwise the harness is shorted.

Likely causes

Signal lead of the B sensor grounded
Vaporizer B sensor shorted internally
Insulation worn through on a long harness run

Symptoms

  • Check engine light, depending on calibration
  • Gas operation limited or switched off
  • Vaporizer B shown far hotter than vaporizer A

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–600
Time0.5–2.5 h

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

Parts involved

alt fuel vaporizer b outlet temp sensorwiring harnessafcm

Related codes

P2A55P2A56P2A58P2A59P2A52

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