FTS Low - Fuel Pump Temperature Sensor Low
Your fuel pump's temperature sensor is reading abnormally low, like a thermometer stuck at freezing when it's actually warm. The engine computer thinks the fuel is too cold and may adjust fuel delivery incorrectly.
The ECU monitors the fuel pump temperature sensor (FTS) to adjust fuel density calculations and injector pulse width. The sensor uses a thermistor that changes resistance based on fuel temperature. When voltage reads lower than expected, the ECU interprets this as abnormally cold fuel.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| FTS Voltage | 0.5-4.5V (approximately -40°F to 250°F) | Below 0.1V or persistent low reading |
| Fuel Temperature | 50-200°F typical operating range | Reading below -20°F (sensor failure) |
Code P1191 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, P1191 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.