What does Error Code P0191 mean?
Moderate Issue
DTC Code P0191 indicates a Fuel Rail Pressure Sensor Circuit Range/Performance issue, where the sensor's output does not align with expected voltage levels, affecting fuel delivery precision. This code is relevant for vehicles with a closed-loop fuel pressure control system, where the sensor's feedback is crucial for the Powertrain Control Module (PCM) to manage injector timing and pulse width effectively.
What are the symptoms of Error Code P0191?
- Engine Light ON: The illumination of the engine light or service engine soon warning light indicates a potential issue with the fuel rail pressure sensor circuit. This is a common symptom when the sensor is not performing within its expected range.
- Engine Will Not Start: A failure to start the engine can occur due to incorrect fuel pressure readings. This may be caused by a malfunctioning fuel rail pressure sensor, which affects the fuel delivery to the engine.
What causes Error Code P0191?
- Low or no fuel can lead to insufficient pressure in the fuel rail, triggering the sensor to detect an anomaly.
- A faulty Fuel Rail Pressure (FRP) sensor may provide incorrect readings, causing the ECU to register a performance issue.
- An open or shorted FRP harness can disrupt the signal transmission, leading to inaccurate pressure readings.
- Poor electrical connections in the FRP circuit can result in intermittent or incorrect sensor data being sent to the ECU.
- A faulty fuel pump may not deliver the required pressure, causing the sensor to detect a deviation from expected values.
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How to fix Error Code P0191?
- Initial Inspection: Inspect the fuel rail pressure sensor and its wiring for any visible damage or disconnections. Ensure all connectors are secure and free from corrosion.
- Check Fuel Pressure: Use a fuel pressure gauge to measure the actual fuel pressure in the rail. Compare the readings with the manufacturer's specifications to determine if the pressure is within the expected range.
- Sensor Voltage Test: With a multimeter, check the voltage at the fuel rail pressure sensor connector. Verify that the voltage is within the specified range as per the vehicle's service manual.
- ECU Communication: Ensure that the Engine Control Unit (ECU) is receiving the correct signal from the fuel rail pressure sensor. Use a scan tool to monitor live data and confirm the sensor's output matches the actual fuel pressure.
- Inspect Fuel System Components: Examine other components of the fuel system, such as the fuel pump and fuel filter, for any signs of malfunction that could affect fuel pressure.
- Perform a Wiring Continuity Test: Check the continuity of the wiring between the fuel rail pressure sensor and the ECU to ensure there are no breaks or shorts in the circuit.