OBD-II reference

All 9.533 generic OBD-II codes, explained in detail.

Causes, inspection steps and sources — a comprehensive DIY archive. Created and maintained with love for the detail. Good luck and have fun!

Powertrain generic / SAE

P2A77

Alternative Fuel Hydraulic Pump Pressure Sensor Circuit Low

Voltage on the alternative fuel hydraulic pump pressure sensor signal line is below the expected window. Wire shorted to ground or sensor short.

SystemPowertrain
Typegeneric / SAE
GroupP2
Range / numberA / 77

Possible causes

  • Signal wire shorted to ground high
  • Internal sensor short medium
  • Connector pins corroded - high contact resistance low

Inspection / repair

  • Difficulty: medium
  • DIY: shop recommended
  • Estimated cost: 200–1000 €
  • Estimated time: 1–4 h
  • Component: alt fuel hyd pump pressure sensor
  • Component: wiring harness
  • Component: afcm
  • MIL / check engine light
  • emissions-relevant
  • limp mode possible

Sources

References

How to read OBD-II codes

The first letter names the vehicle system, the second digit distinguishes generic from manufacturer-specific, the remaining digits group fault area and number.

PPowertrain: engine, transmission, emissions
BBody: chassis trim, comfort, interior
CChassis: suspension, brakes, steering
UNetwork: CAN, control modules, communication