P1173: Low Fuel Rail Pressure
The PCM has detected that the fuel rail pressure (FRP) sensor signal is below the minimum calibrated value for the current engine load and RPM, even though the signal is within the sensor's valid electrical range (no open or short circuit). This indicates either actual low fuel pressure or a sensor drift toward low readings, leading to a lean air-fuel mixture.
01. Most Common Causes
- Faulty or drifting fuel rail pressure (FRP) sensor
- Weak or failing fuel pump
- Fuel pressure regulator stuck open or leaking internally
- Clogged fuel filter
- Leaking fuel injectors (internal drip)
- High resistance or corrosion in FRP sensor wiring/connector
- Faulty PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine hesitation, rough idle, or stalling
- Poor acceleration and reduced power
- Hard starting or extended cranking
- Decreased fuel economy
03. Step-by-Step Diagnosis
Scan for codes and verify P1173 is present; check freeze frame data for engine load and RPM at time of fault.
Inspect FRP sensor connector and wiring for corrosion, damage, or loose pins.
Monitor FRP sensor voltage with a scan tool while engine is running; compare to manufacturer specifications.
Perform a fuel pressure test at the rail using a mechanical gauge to confirm actual pressure.
Check fuel pump operation, fuel filter condition, and regulator function based on pressure readings.
If pressure is low and sensor reads correctly, inspect injectors for leakage and replace as needed.
1. Frequently Asked Questions
Is it safe to drive?▼
Driving with P1173 is not recommended as low fuel pressure can cause a lean mixture, potentially leading to engine misfire, overheating, or catalytic converter damage. Have the vehicle diagnosed and repaired promptly.
How much does it cost to fix?▼
Repair costs vary widely depending on the root cause: FRP sensor replacement $100-$250, fuel pump $400-$800, fuel filter $50-$150, injector service $200-$600. Diagnosis typically adds $100-$150.