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DTC P0171: 1/1 Fuel System Lean: Testing

NOTE: Before proceeding, check for contaminants that may have damaged O2 sensor such as contaminated fuel, unapproved silicone, oil and coolant.
  1. Turn the ignition on. With the DRBIII(R), 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. WARNING: Fuel system is under constant pressure even when ignition is off. Open fuel system with caution.
  2. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Connect fuel pressure gauge to fuel rail. Turn the ignition on. With the DRBIII(R), actuate the Automatic Shutdown (ASD) Fuel System test and observe the fuel pressure gauge. Fuel pressure specification is 53-63 psi (365-434 kPa). Turn the ignition off. Stop all actuations. Choose a conclusion that best matches your fuel pressure reading. If fuel pressure is within specification, go to next step. If fuel pressure is more than specification, replace the fuel filter pressure regulator. If fuel pressure is less than specification, go to step  13 .
  3. Stop all actuations. With the DRBIII(R), read the O2 sensor voltage. Is the voltage 0.4-0.6 volt? If yes, go to next step. If no, go to step  10 .
    4. NOTE: Turn the ignition off and wait at least 10 minutes to allow O2 sensor to cool until O2 sensor voltage has stabilized to 0.4-0.6 volt.
  4. Turn the ignition on. With the DRBIII(R), actuate the O2 sensor Heater Test. With the DRBIII(R), monitor O2 sensor voltage for at least 2 minutes. Does the voltage stay 0.4-0.6 volt. If yes, replace the O2 sensor. If no, go to next step.
    5. NOTE: The throttle must be against the stop.
  5. Stop all actuations. With the DRBIII(R), read TP sensor voltage. 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 TP sensor.
  6. With the DRBIII(R), read the TP sensor voltage while slowly opening and closing the throttle. Does the voltage increase and decease smoothly? If yes, go to next step. If no, replace the TP sensor.
    7. NOTE: If engine will not idle, maintain a constant RPM above idle.
  7. Turn the ignition off. Connect a vacuum gauge to a manifold vacuum source. Start the engine. Allow the engine to idle. With the DRBIII(R) in Sensors, read the MAP sensor Vacuum value. Is the DRBIII(R) reading within one in. Hg of the vacuum gauge reading? If yes, go to next step. If no, replace the MAP sensor.
    8. NOTE: For this test to be valid, the thermostat must be operating correctly. This test works best if performed on a cold engine (cold soak). If engine coolant temperature is more than 180°F (82°C), allow the engine to cool until 150°F (65°C) is reached.
  8. Turn the ignition off. Turn the ignition on. With the DRBIII(R), read the ECT sensor value. If the engine was allowed to sit overnight (cold soak), the sensor value should be approximately equal to the ambient temperature. Start the engine. Allow the engine to idle. 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 ECT value increase smoothly and did it reach at least 180°F (82°C)? If yes, go to next step. If no, replace the ECT sensor.
  9. Check for any of the following conditions/mechanical problems:
    • Ensure air induction system is free from leaks.
    • Ensure engine vacuum is at least 13 in. Hg at idle in Park or Neutral.
    • Ensure valve timing is within specification.
    • 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 plugged or restricted.
    • Ensure fuel injector harness connectors are connected to correct fuel injectors.

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

  10. Turn the ignition off. Disconnect the O2 sensor harness connector. Turn the ignition on. With the DRBIII(R), monitor the O2 sensor voltage. Is the O2 sensor voltage 0.40-0.60 volt? If yes, replace the O2 sensor. If no, go to next step.
  11. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance between ground and the O2 sensor signal circuit in the PCM harness connector. Is the resistance less than 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.
    13. WARNING: Fuel system is under constant pressure even when ignition is off. Open fuel system with caution.
  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 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(R), actuate the ASD Fuel System test and observe the fuel pressure gauge. Fuel pressure specification is 53-63 psi (365-434 kPa). Is the fuel pressure within specification? If yes, repair or replace fuel supply line as necessary. If no, go to next step.
    14. WARNING: Fuel system is under constant pressure even when ignition is off. Open fuel system with caution.
  14. Turn the ignition off. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Remove the fuel pump module and inspect the fuel inlet strainer. Is the fuel inlet strainer plugged? If yes, replace the fuel inlet strainer. If no, go to next step.
  15. There are no possible causes remaining, replace 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 O2 sensor such as contaminated fuel, unapproved silicone, oil and coolant.
  16. Conditions that set DTC are not present at this time. The following list may help in identifying the intermittent condition:
    • With the engine running at normal operating temperature, monitor the DRBIII(R) 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(R) Freeze Frame information to identify under what conditions the DTC set.
    • Refer to any Technical Service Bulletin (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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