Fuel Rail Sensor In-Range Low Failure
The fuel rail pressure sensor is reading lower than expected, similar to a tire pressure gauge that consistently shows less air than actually present. The ECU detects this signal is stuck in a low range and cannot trust the fuel pressure data for proper engine control.
The ECU monitors the fuel rail pressure sensor voltage output to ensure fuel pressure stays within operating range (typically 40-80 PSI at idle, higher under load). When the sensor signal remains abnormally low and doesn't respond to expected pressure changes, the ECU logs this in-range low failure code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Fuel Rail Pressure | 40-80 PSI idle, 60-120 PSI loaded | Consistently below 35 PSI or sensor voltage stuck low |
| Sensor Voltage | 0.5-4.5 volts across operating range | Voltage stuck below threshold for extended duration |
Code P1173 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P1173 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.