Powertrain, generic (extended)

P2A42 Alternative Fuel Tank B Pressure Sensor Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Unlike its electrical siblings, P2A42 deals with a tank B pressure reading that is electrically valid but makes no sense. Examples: the value does not fall while gas is drawn from tank B, it stays frozen after refuelling, or it differs clearly from the pressure of the other cylinders after a long stop, when all tanks connected to one fill line should settle at about the same level. New Flyer's bulletin SMB-169 for CNG buses gives a sense of the scale: after filling, the high-pressure gauge is expected to show between 200 and 3,600 psi. A tank valve stuck closed (P2A23) or a closed hand valve also starves the reading of change. No manufacturer publishes P2A42 or its limits; CARB requires a rationality check for such inputs. Diagnosis compares the sensor with a mechanical gauge.

Likely causes

Tank B pressure sensor drifting or stuck
Tank B solenoid stuck closed or manual valve shut
Contact resistance in the sensor connector shifting the signal

Symptoms

  • Check engine light
  • Gas gauge implausible after refuelling or driving
  • Reduced range on gas

Repair estimate

DifficultyHardWorkshop job
Parts and labour€100–900
Time1–3 h

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

Parts involved

alt fuel tank b pressure sensorwiring harnessafcm

Related codes

P2A41P2A43P2A44P2A23P019F

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