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DTC P0171: 1/1 Fuel System Lean: Testing

NOTE: Check for contaminates that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil or coolant.
  1. Turn ignition on. Using scan tool, read DTCs. If GOOD TRIP counter is displayed and equal to zero, go to next step. If GOOD TRIP counter is not displayed and equal to zero, go to step  16 .
    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  . Install fuel pressure gauge to fuel rail. On 2.7L engines, use Fuel Adapter (6539). On all engines, turn ignition on. Using scan tool, actuate ASD FUEL SYSTEM TEST. Observe fuel pressure gauge. Note fuel pressure reading, stop ASD FUEL SYSTEM TEST and turn ignition off. Fuel pressure should be 53-63 psi (365-434 kPa). If fuel pressure is as specified, go to step  6 . If fuel pressure is less than specified, go to next step. If fuel pressure is more than specified, replace fuel filter/pressure regulator.
  3. Release fuel pressure. Raise and support vehicle. Disconnect fuel pressure line from fuel pump module. Connect 5/16 Fuel Line Adapter (6539) between disconnected fuel line and fuel pump module. Connect fuel pressure gauge to "T" on fuel line adapter. Turn ignition on. Using scan tool, actuate ASD FUEL SYSTEM TEST. Observe 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.
  4. Remove fuel pump module from fuel tank. Inspect fuel inlet strainer. If fuel inlet strainer is plugged, replace fuel inlet strainer. If fuel inlet strainer is not plugged, go to next step.
  5. If no other possible causes are remaining, fuel pump module is assumed to be defective. Replace fuel pump module.
  6. Turn ignition on. Using scan tool, read 1/1 HO2S voltage. If voltage is .4-.6 volt, go to next step. If voltage is not .4-.6 volt, go to step  13 .
  7. Turn ignition off. Wait at least 10 minutes for HO2S to cool. Turn ignition on. Using scan tool, actuate 1/1 HO2S heater test. Using scan tool, monitor 1/1 HO2S voltage for at least 2 minutes. If voltage stays between .4 and .6 volt, replace 1/1 HO2S. If voltage does not stay between .4 and .6 volt, go to next step.
  8. Using scan tool, read TP sensor voltage. Ensure throttle is fully closed and against stop. If voltage is .92 volt or less, go to next step. If voltage is more than .92 volt, check for binding throttle. Repair throttle as necessary. If throttle is not binding, replace TP sensor.
  9. While monitoring TP sensor voltage on scan tool, slowly open and close throttle. If voltage increases and decreases smoothly in response to throttle opening and closing, go to next step. If voltage does not increase and decrease smoothly in response to throttle opening and closing, replace TP sensor.
  10. Turn ignition off. Connect a vacuum gauge to a manifold vacuum source. Start engine and let it idle. If engine will not idle, slightly open throttle and maintain a constant RPM. Using scan tool, read MAP sensor vacuum value. If vacuum gauge reading is within one in. Hg of scan tool display, go to next step. If vacuum gauge reading is not within one in. Hg of scan tool display, replace MAP sensor.
    NOTE: Thermostat must be operating properly for the following test to be valid. This test works best if performed on a cold engine.
  11. Turn ignition on. Using scan tool, read ECT sensor value. If engine was allowed to sit overnight, ECT sensor value should be near ambient air temperature value. If ECT sensor value is more than 180°F (82.2°C), allow engine to cool until ECT sensor value is 150°F (65.5.°C) before proceeding. If ECT sensor value is 150°F (65.5°C) or less, start engine. Using scan tool, monitor ECT sensor value until it reaches 180°F (82.2°C). ECT sensor value should increase smoothly from start-up to normal operating temperature and should reach at least 180°F (82.2°C). If ECT sensor value increased smoothly and reached at least 180°F (82.2°C), go to next step. If ECT sensor value did not increase smoothly or did not reach at least 180°F (82.2°C), replace ECT sensor.
  12. Check for any of the following conditions:
    • 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.

    If a problem exists, repair as necessary. If no problems exist, test is complete.

  13. Disconnect 1/1 HO2S harness connector. Using scan tool, read 1/1 HO2S voltage. If voltage is .4-.6 volt, replace 1/1 HO2S. If voltage is not .4-.6 volt, go to next step.
  14. Turn ignition off. Disconnect PCM harness connectors. See Figure . Measure resistance between ground and signal circuit (Black/Dark Green wire) at 1/1 HO2S harness connector. If resistance is more than 5 ohms, go to next step. If resistance is 5 ohms or less, repair short to ground in Black/Dark Green wire.
  15. If no other possible causes are remaining, PCM is assumed to be defective. Replace PCM.
  16. Conditions that set DTC are not present at this time. Perform the following to help identify intermittent condition:
    • With engine running at normal operating temperature, wiggle related wiring harness while monitoring related parameters on scan tool. If voltage changes or DTC sets while wiggling wiring harness, repair connectors or wiring harness where wiggling caused voltage to change or DTC to set.
    • Review freeze frame information on scan tool. Duplicate conditions present when DTC was set.
    • Refer to any technical service bulletins that may apply.
    • Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires.
    • Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals.

    If a problem is found, repair as necessary. If no problems are found, test is complete.

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