Powertrain, generic (extended)

P2A7C Alternative Fuel Hydraulic Pressure Sensor Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2A7C is set when the hydraulic pressure sensor signal falls below its valid band, most often from a signal wire grounded against the chassis, an open 5 V reference or a sensor with an internal short. If this sensor watches the return side, as in one of Caterpillar's layouts, a dead-low reading would hardly stand out at first, since return pressure is low anyway; the range check against the minimum voltage still catches it. On the drive side a low value can mask the pressure rise that marks a completed stroke. The control may then rely on the remaining sensor or stop the LNG pump. Where both pressure sensors share a reference wire, check whether P2A77 is stored too. No manufacturer documents P2A7C or its thresholds.

Likely causes

Signal wire grounded against chassis or hydraulic lines
Open 5 V reference to the sensor
Sensor shorted internally

Symptoms

  • Warning lamp on
  • Pump stops or delivers less LNG
  • Additional sensor codes if the reference is shared

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 hyd pressure sensorwiring harnessafcm

Related codes

P2A7AP2A7BP2A7DP2A7EP2A77

References: law.cornell.edu, patents.google.com.