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Home >> Chrysler >> 2001 >> Neon LE, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0171: 1/1 Fuel System Lean >> Testing
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DTC P0171: 1/1 Fuel System Lean: Testing

NOTE: Before proceeding, check for contaminates that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil and coolant.
  1. Turn ignition on. Using scan tool, read DTCs. If GOOD TRIP is displayed and equal to zero, go to next step. If GOOD TRIP 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  . Connect fuel pressure gauge to fuel rail. Turn ignition on. Using scan tool, 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, go to step  6 . If fuel pressure is less than specification, go to next step. If fuel pressure is more than specification, replace fuel filter/pressure regulator.
  3. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  . Raise vehicle on hoist. 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, 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 to allow HO2S to cool until HO2S voltage has stabilized to .4-.6 volt. Turn ignition on. Using scan tool, actuate O2 HEATER TEST. Using scan tool, monitor 1/1 HO2S voltage for at least 2 minutes. If voltage does not remain between .4 and .6 volt, go to next step. If voltage remains between .4 and .6 volt, replace 1/1 HO2S.
  8. Turn ignition on. Using scan tool, read TP sensor voltage. Ensure throttle is against throttle stop. If voltage is .92 volt or less with throttle closed, go to next step. If voltage is more than .92 volt with throttle closed, check for binding throttle. Repair 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, go to next step. If voltage does not increase and decrease smoothly, replace TP sensor.
  10. Turn ignition off. Connect a vacuum gauge to manifold vacuum. Start engine and let it idle. If engine will not idle, maintain a constant RPM above idle. Using scan tool, read MAP sensor vacuum value. If scan tool value is within one in. Hg of vacuum gauge reading, go to next step. If scan tool value is not within one in. Hg of vacuum gauge reading, replace MAP sensor.
    NOTE: For the following test to be valid, thermostat must be operating correctly. This test works best if engine was allowed to cool overnight.
  11. Turn ignition off then on. Using scan tool, read ECT sensor value. If engine was allowed to cool overnight, ECT sensor value should be close to ambient temperature. If engine coolant temperature is more than 180°F (82°C), allow engine to cool until 150°F (66°C) is reached. Start engine. During engine warm-up, ECT sensor value should increase smoothly to at least 180°F (82°C). If operation is as specified, go to next step. If operation is not as specified, 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 any problems exist, repair as necessary. If no problems exist, test is complete.

  13. With ignition on, disconnect 1/1 HO2S harness connector. Using scan tool, read 1/1 HO2S voltage. If voltage is not .4-.6 volt, go to next step. If voltage is .4-.6 volt, replace 1/1 HO2S.
  14. Turn ignition off. Disconnect PCM harness connectors. PCM is located in engine compartment, between air cleaner and radiator. Measure resistance of signal circuit (Black/Dark Green wire) between 1/1 HO2S harness connector and terminal No. 30 at PCM C1 harness connector. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in signal circuit.
  15. If no other possible causes are remaining, 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 (TSBs) 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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