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DTC P0171: 1/1 Fuel System Lean: Testing

    NOTE: Check for contaminants that may have damaged the O2 Sensor such as contaminated fuel, unapproved silicone, oil and coolant.
    WARNING: Fuel system is under constant pressure even when ignition is off. Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released.
  1. Turn the ignition on. With the DRBIII®, read DTCs. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  16.
  2. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Connect fuel pressure gauge to fuel rail. Turn ignition on. With the DRBIII®, actuate ASD Fuel System test and observe fuel pressure gauge. Fuel pressure should be 53-63 psi (365-434 kPa). Turn ignition off. If fuel pressure is within specification, stop all actuations and go to next step. If fuel pressure is less than specification, stop all actuations and go to step  13. If fuel pressure is more than specification, stop all actuations. Replace fuel filter/pressure regulator.
  3. Turn the ignition on. With the DRBIII®, read the O2 Sensor voltage. Is the voltage between 0.4 to 0.6 volt? If yes, go to next step. If no, go to step  10.
  4. Turn the ignition off. Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Allow the O2 Sensor voltage to stabilize between 0.4 to 0.6 volt. Turn the ignition on. With the DRBIII®, actuate the O2 Heater Test. With the DRBIII®, monitor O2 Sensor voltage for at least 2 minutes. Does the voltage stay between 0.4 and 0.6 volt? If yes, replace the O2 Sensor. If no, go to next step.
  5. Turn the ignition on. With the DRBIII®, read TP Sensor voltage. The throttle must be against the stop. Is the voltage 0.92 volt or less with the Throttle closed? If yes, go to next step. If no, check for a binding throttle condition. If okay, replace the Throttle Position Sensor.
  6. Turn the ignition on. With the DRBIII®, read the TP Sensor voltage. While monitoring the DRBIII®, slowly open and close the throttle. Does the voltage increase and decrease smoothly? If yes, go to next step. If no, replace the Throttle Position Sensor.
  7. Turn the ignition off. Connect a Vacuum Gauge to a Manifold Vacuum source. Start the engine. Allow the engine to idle. If engine will not idle, maintain a constant RPM above idle. With the DRBIII® in Sensors, read the MAP Sensor vacuum value. Is the DRBIII® reading within 1 in. Hg of the Vacuum Gauge reading? If yes, go to next step. If no, replace the MAP Sensor.
  8. For this test to be valid, the thermostat must be operating correctly. This test works best if performed on a cold engine (cold soak). Turn the ignition on. With the DRBIII®, read the Engine Coolant Temperature (ECT) Sensor value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature. If engine coolant temperature is above 180°F (82°C), allow the engine to cool until 150°F (65°C) is reached. Start the Engine. During engine warm-up, monitor the ECT Sensor value. The temperature value change should be a smooth transition from start up to normal operating temperature 180°F (82°C). The value should reach at least 180°F (82°C). Did the Engine Coolant Temperature value increase with a smooth transition and did it reach at least 180°F (82°C)? If yes, go to next step. If no, replace the Engine Coolant Temperature Sensor.
  9. Check for any of the following conditions/mechanical problems:
    • Ensure air intake system is free from leaks.
    • Ensure engine vacuum is at least 13 in. Hg at idle in Park or Neutral.
    • Ensure valve timing is correct.
    • Ensure engine compression is within specification.
    • Ensure exhaust system is free from restrictions or leaks.
    • Ensure PCV system flows freely.
    • Ensure torque converter stall speed is within specification.
    • Ensure power brake booster has no internal vacuum leaks.
    • Ensure fuel is not contaminated.
    • Ensure fuel injectors are not restricted.
    • Ensure fuel injector harness connectors are connected to correct fuel injectors.

    Are there any engine mechanical problems? If yes, repair as necessary. If no, test is complete.

  10. Turn the ignition on. Disconnect the O2 Sensor harness connector. With the DRBIII®, monitor the O2 Sensor voltage. Is the O2 Sensor voltage between 0.4 to 0.6 volt? If yes, replace the O2 Sensor. If no, go to next step.
  11. Turn the ignition off. Disconnect the O2 Sensor harness connector. Disconnect the PCM C1 harness connector. Measure the resistance of the O2 Sensor Signal circuit in the PCM C1 harness connector to ground. Is the resistance below 5.0 ohms? If yes, repair the O2 Sensor Signal for a short to ground. If no, go to next step.
  12. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
    13. WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released.
  13. Turn the ignition off. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module. Install special 5/16 Fuel Line Adapter (6539) between disconnected fuel line and the fuel pump module. Attach a fuel pressure test gauge to the "T" fitting on fuel line adapter. Turn the ignition on. With the DRBIII®, actuate the ASD Fuel System test and observe the fuel pressure gauge. Note fuel pressure reading, stop ASD Fuel System test and turn ignition off. If fuel pressure is 53-63 psi (365-434 kPa), repair or replace fuel supply line as necessary. If fuel pressure is not 53-63 psi (365-434 kPa), go to next step.
  14. Release fuel pressure. Remove fuel pump module from fuel tank. Inspect fuel inlet strainer. Is the fuel inlet strainer plugged? If yes, replace fuel inlet strainer. If no, go to next step.
  15. There are no possible causes remaining, replace the Fuel Pump Module.
    16. WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
    NOTE: Check for contaminants that may have damaged the O2 Sensor such as contaminated fuel, unapproved silicone, oil and coolant.
  16. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
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