P1291 — Fuel pressure regulation efficiency / blocking

Diagnostic algorithm

1. Read and record all DTCs and freeze frame data. Note engine conditions (rpm, temp, load).
2. Check obvious items: fuel level, wiring/connectors to pressure sensor and pressure control valve, fuses and relays.
3. Visually inspect fuel lines, feed and return, filter and tank vent for restrictions or contamination.
4. Using a calibrated fuel pressure gauge, measure rail/feed pressure at key conditions: key‑on prime, crank, idle and under commanded pressure changes.
5. Using a scan tool, monitor fuel rail pressure sensor reading while commanding the pressure control valve; compare gauge vs sensor. If sensor and gauge disagree, suspect sensor or wiring.
6. Command the pressure control valve/solenoid (active test) and observe pressure change and solenoid current/duty. If no movement, test solenoid resistance and supply. Repair/replace as required.
7. Test low‑pressure pump supply pressure and flow; replace pump or clean strainer if below spec.
8. Check return line for restriction (disconnect return to tank where safe) and inspect for collapsed hoses or blocked check valves.
9. If low/high pressure persists after low‑pressure system and control valve tested OK, investigate high‑pressure pump and injector return leaks. Repair or replace defective high‑pressure components per manufacturer procedure.
10. After repairs, clear codes and perform road test and recheck for recurrence. If intermittent, consider fuel contamination or tank internal issues.