What it means
The AFCM detects a generic fault on the pressure sensor at the inlet of the alternative fuel rail pressure regulator. Regulator inlet pressure cannot be monitored reliably.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
A pressure sensor at the inlet of the alternative-fuel rail pressure regulator reports incoming rail pressure to the alternative-fuel control module. This circuit code sets when the module detects a fault that prevents it from monitoring that inlet pressure reliably.
Common causes
Most likely first.
- Pressure sensor failed
- Wiring or connector fault
Symptoms
- Check-engine or alternative-fuel system warning light
- Rough running or hesitation on alternative fuel
- Alternative-fuel operation may be limited
How to diagnose it
- Record freeze-frame data and check live inlet-pressure data to see whether the fault coincides with rough running, hesitation, or a switch in fuel mode.
- Inspect the regulator inlet pressure sensor connector and harness for loose connections, corrosion, heat damage, or chafing.
- Check the sensor supply, ground, and signal circuits using the vehicle's wiring information and the manufacturer's specification.
- Compare the sensor reading with the manufacturer's specified pressure test or a suitable independent measurement, using the required alternative-fuel safety procedure.
- Test the sensor output and circuit continuity to determine whether the fault is in the sensor or its wiring.
Common fixes
- Secure the sensor connector and repair damaged or corroded terminals.
- Repair wiring or ground faults in the regulator inlet pressure sensor circuit.
- Replace the inlet pressure sensor if its output fails the manufacturer's checks.
- Correct a sensor mounting problem if inspection confirms it is loose.
Can I keep driving?
Rough running or hesitation can occur, and the system may limit alternative-fuel operation or enter a reduced-power mode. Avoid demanding acceleration or driving in traffic if the engine runs unpredictably; have the pressure fault checked promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.