P0191 Code - Fuel Rail Pressure Sensor Circuit Range/Performance

What Does P0191 Mean?

The power control module (PCM) regulates the amount of fuel that is released into the combustion chambers by controlling the fuel injectors. This process works to reduce tailpipe emissions. In order to work effectively, the power control module must always know what the fuel pressure is. If the fuel rail pressure sensor is giving inconsistent readings, the power control module (PCM) will store the P0191 trouble code.

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What are the common causes of P0191 ?

Depending on year, make, and model, DTC P0191 may have number of causes. Here are some of the most common.

• RPS Failure – The fuel rail pressure sensor, like most semiconductor sensors, is prone to failure from heat and vibration, both of which are present in abundance in the engine compartment. This is the most common failure in the system.

What are the symptoms of P0191 ?

Symptoms of a P0191 diagnostic trouble code may include:

• The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.
• Faulty PCM
• If the DPF is not cleared the ECU will revert to the "Limp Home Mode" until the situation is corrected
• Diminished fuel efficiency

How do you troubleshoot P0191 ?

A Range/Performance related code will be set when either a sensor or other component does not perform within the range the PCM (Powertrain Control Module) expects to see, given the current engine load/speed, and information gathered from other sensors. The possible causes of Range/Performance codes are likely to be defective sensors as easily as they are likely to be the result of wiring issues that affect the operation of the affected sensor or component, which means that with P0191, it is important to regard all sensors and components as part of the control circuit the code refers to.



Depending on the vehicle, the RPS generally has an operating voltage range. Some Toyota RPS, for example, function between 0.5 V and 4.5 V, measuring 0 psi to 1,885 psi. To diagnose the RPS and its circuit, you’ll need a DMM (digital multimeter) and vehicle-specific EWD (electrical wiring diagram) and repair manuals.

General Check – Check wire harnesses for obvious damage, such as from chafing, poor routing, or other damage. Check connectors for bent or broken pins or corrosion. Make sure all connectors seat properly. Repair as necessary.

Circuit Check – Disconnect the ECM and RPS. If no circuit problems are found, suspect a faulty sensor, but test (if possible) before replacing it.

• Check each line for continuity end to end. Resistance should be less than 1 Ω. Repair as necessary.
• Check each line for short to each other and to ground. Resistance should be over 10 kΩ. Repair as necessary.

Sensor Check – All connectors firmly seated and KOEO (key on engine off), backprobe the RPS or ECM and check voltage against repair manual specifications. Using our Toyota example, there should be a 5 V reference voltage (Vref), ECM ground, and RPS signal. If circuit checks and sensor checks pass, suspect and ECM fault, but do not condemn the ECM until you have the system checked by a professional.

• If Vref, RPS, and Ground is 4.5 – 5.5 V, suspect an open ground circuit. If you’ve ruled out the circuit itself, it may be internal. Repair wire harness or replace sensor.
• If Vref is 4.5 – 5.5 V and Ground is 0 V, RPS should read between 0.5 V and 4.5 V. If otherwise, replace the sensor.
• You may be able to measure resistance directly on some pressure sensors. Disconnect the sensor and measure across the terminals, comparing to repair manual specifications. If outside of specification, replace the sensor.

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