Fuel and air

P01A8 — Alternative Fuel Rail Pressure Too Low

Severity: medium Drive with care, to a shop

What P01A8 means

The engine control module compares the pressure in the alternative fuel rail (CNG, LPG or ethanol such as E85) with the expected value. If the sensor reports pressure below the allowed range, it stores P01A8. The cause can be a real fuel delivery shortage or a faulty sensor or circuit.

Symptoms

  • Check Engine light on
  • Reduced power and sluggish acceleration
  • Rough idle or hesitation
  • Poor fuel economy
  • Hard starting or stalling
  • Automatic switch to gasoline on bi-fuel vehicles

Possible causes

  1. True low pressure from a weak pump or failing pressure regulator
  2. Faulty rail pressure sensor
  3. Clogged fuel filter
  4. Contaminated or poor-quality fuel, or a nearly empty tank/cylinder
  5. Fuel leak or air leak in the lines
  6. Open, corroded or shorted sensor wiring and connectors

How to diagnose

  1. Scan all codes and freeze frame data and look for other fuel system codes
  2. Confirm there is enough fuel of the correct type and quality
  3. Inspect lines, fittings and connectors for leaks, damage and corrosion
  4. Compare the scan tool rail pressure reading with a mechanical gauge
  5. Test sensor power, ground and reference voltage with a multimeter
  6. Check the fuel filter, pump and regulator, and measure pressure under load
  7. Test the alternative fuel injectors and shutoff valves

Common fixes

  • Replace the rail pressure sensor
  • Replace the fuel pump, regulator or filter
  • Repair leaks and replace damaged lines
  • Repair the wiring harness and connectors
  • Drain contaminated fuel and clean the system

Questions and answers

What does P01A8 mean?

The control module detected alternative fuel rail pressure below the expected level. The cause may be fuel delivery, the sensor or its wiring.

Can I drive with P01A8?

Only briefly and carefully, preferably on gasoline if available. Extended driving on a lean mixture risks engine and catalytic converter damage.

What should I check first?

Fuel level and quality, the filter, the sensor connector and wiring, then compare actual pressure on a gauge with the scan tool reading.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.