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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 433 (Engine Controls - Self-Diagnostics - 6.0L Bi-Fuel & CNG) >> Diagnostic Tests >> DTC P0191: Fuel Rail Pressure Sensor Circuit Performance >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Alternative Fuels - Engine Controls. If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn ignition on, with engine off. Using a scan tool, observe the Fuel Rail Pressure (FRP) parameter. If the scan tool displays the FRP sensor parameter within 120-220 psi (827-1517 kPa), go to next step. If the scan tool does not display the FRP sensor parameter within 120-220 psi (827-1517 kPa), go to step  4.
  3. Observe the Freeze Frame and/or the Failure records data for this DTC. Turn the ignition OFF for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure records data. If the DTC failed this ignition cycle, go to next step. If the DTC did not fail this ignition cycle, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  4. Turn ignition on, with engine off. Using a scan tool, command the LPL on and off. Listen for operation of the LPL. If the operation of the LPL can be heard, go to next step. If the operation of the LPL can not be heard, see DTC P2665: INCORRECT VOLTAGE DETECTED - LOW PRESSURE LOCK-OFF SOLENOID .
  5. Disconnect the FRP sensor. Using a test light connected to battery positive, probe the FRP sensor low reference circuit. If the test light illuminates, go to next step. If the test light does not illuminate, go to step  10.
  6. Probe the FRP sensor 5-volt reference circuit with a test light connected to a good ground. Measure the voltage drop across the test light with a DVOM. If the voltage reading is 5 volts, go to next step. If the volage reading is not 5 volts, go to step  11.
  7. Connect a 3-amp fused jumper wire between the signal circuit and the 5-volt reference circuit of the FRP sensor. Using a scan tool, observe the FRP sensor data display. If the scan tool displays a FRP sensor voltage of more than 4.95 volts, go to step  9. If the scan tool displays a FRP sensor voltage of less than 4.95 volts, go to next step.
  8. Test the FRP sensor signal circuit for an open or high resistance. Did you find and correct an open or high resistance? If yes, go to step  15. If no, go to step  12.
    9. NOTE: Return to this diagnostic procedure, after performing the Fuel System Diagnosis.
  9. Perform Fuel System Diagnosis, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article. Did you find and correct the condition? If yes, go to step  15. If no, go to step  13.
  10. Test the FRP sensor low reference circuit for high resistance. Did you find and correct a high resistance? If yes, go to step  15. If no, go to step  12.
  11. Test the FRP sensor 5-volt reference circuit for high resistance. Did you find and correct a high resistance? If yes, go to step  15. If no, go to next step.
  12. Test for an intermittent and/or a poor connection at the Fuel Injection Control Module (FICM). Did you find and correct an intermittent and/or a poor connection? If yes, go to step  15. If no, go to step  14.
  13. Replace the FRP sensor. After replacement is complete, go to step  15.
  14. Replace the FICM. After replacement is complete, go to next step.
  15. Using a scan tool, clear the DTCs. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. If the DTC failed this ignition cycle, go to step  2. If the DTC did not fail this ignition cycle, go to next step.
  16. Observe the Capture Info using a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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