Advanced Diagnostics

Advanced Diagnostics

DTC P0191: Fuel Rail Pressure Sensor Circuit Range/Performance Problem






General Description
The compressed natural gas (CNG) is supplied from the fuel tank, and it is regulated to about 250 kPa (depending on the MAP sensor value) by the fuel pressure regulator before it reaches the engine. The powertrain control module (PCM) monitors the fuel pressure value detected by the fuel pressure sensor (PF2A) to maintain the correlation with the MAP sensor value. The PCM uses Modes 1 and 2 based on the correlation between the MAP and PF2A shown in the graph to detect abnormal sensor output characteristics.
Mode 1: If the variance of PF2A is within a set range when the MAP varies beyond a certain value, no malfunction is detected, and Mode 2 is started. If the variance of PF2A is out of a set range, a malfunction is detected and a DTC is stored. Mode 2: If the calculated PF2S is out of a set range, a malfunction is detected and a DTC is stored.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status






Enable Conditions






Malfunction Threshold
Mode 1: The difference between PF2A values when the MAP is maximum and when the MAP is minimum is 4 bits or less.
Mode 2: PF2A is not between 204 - 326 kPa (2.1 - 3.3 kgf/cm2, 30 - 47 psi) for at least 3 seconds. (PF2S = PF2A - MAP)

Driving Pattern






1. Start the engine. Hold the engine speed at 3,000 rpm without load (in Park or neutral) until the radiator fan comes on.
2. Drive the vehicle, and gradually accelerate and decelerate for at least 1 second. (Mode 1)
3. Then, drive at a speed between 35 - 75 mph (56 - 120 km/h) for at least 3 seconds. (Mode 2)

- If you have difficulty duplicating the DTC, retest after turning off electrical components such as the audio system and A/C, and try a different gear position.
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

Diagnosis Details

Conditions for illuminating the MIL
When a malfunction is detected during the first drive cycle, a Temporary DTC is stored in the PCM memory. If the malfunction recurs during the next (second) drive cycle, the MIL comes on and the DTC and the freeze frame data are stored.

Conditions for clearing the MIL
The MIL will be cleared if the malfunction does not recur during three consecutive trips in which the diagnostic runs. The MIL, the DTC, the Temporary DTC, and the freeze frame data can be cleared by using the scan tool Clear command or by disconnecting the battery.