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Home >> Jeep >> 2003 >> Wrangler SE, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0171: 1/1 Fuel System Lean Or DTC P0174: 2/1 Fuel System Lean >> Testing

DTC P0171: 1/1 Fuel System Lean Or DTC P0174: 2/1 Fuel System Lean: Testing

    NOTE: Check for contaminants that may have damaged the O2 Sensor such as contaminated fuel, unapproved silicone, oil and coolant.
  1. Turn ignition on, engine not running. 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 INTERMITTENT CONDITION  under SELF-DIAGNOSTIC SYSTEM.
    2. 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. See FUEL SYSTEM PRESSURE RELEASE .
  2. Install a fuel pressure gauge to the fuel rail. Turn ignition on, engine not running. With the DRBIII®, actuate the ASD Fuel System test and observe the fuel pressure gauge. Fuel pressure should be 44.2-54.2 psi (3.23-3.96 kg/cm2 ). Turn the ignition off. Choose a conclusion that best matches your fuel pressure reading. If fuel pressure is below specification, stop all actuations and go to next step. If fuel pressure is within specification, stop all actuations and go to step  6. If fuel pressure is above specification, stop all actuations. Replace the fuel pressure regulator and fuel filter. See FUEL SYSTEMS in REMOVAL & INSTALLATION - WRANGLER article.
    3. 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. See FUEL SYSTEM PRESSURE RELEASE .
  3. Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module. Connect 5/16" Fuel Line Adapter (6539) or 3/8" Fuel Line Adapter (6631) between disconnected fuel line and the fuel pump module. Attach a fuel pressure test gauge to the "T" fitting on fuel line adapter hose. Turn ignition on, engine not running. With the DRBIII®, actuate the ASD Fuel System test and observe the fuel pressure gauge. Fuel pressure should be 44.2-54.2 psi (3.23-3.96 kg/cm2 ). Is the fuel pressure within specification? If yes, stop all actuations and repair or replace fuel supply line as necessary. If no, stop all actuations and go to next step.
  4. Turn the ignition off. Release fuel pressure. Remove the Fuel Pump Module and inspect the Fuel Inlet Strainer. See FUEL SYSTEMS in REMOVAL & INSTALLATION - WRANGLER article. Is the Fuel Inlet Strainer plugged? If yes, replace the Fuel Pump Inlet Strainer. If no, go to next step.
  5. There are no possible causes remaining, replace the Fuel Pump Module.
    6. NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor and Exhaust System to cool down before continuing the test.
  6. Ignition on, engine not running. With the DRBIII®, read the O2 Sensor voltage. Is the voltage above 4.5 volts? If yes, go to the next step. If no, go to step  13.
  7. Turn ignition off. Wait at least 10 minutes to allow HO2S to cool down before continuing the test. Turn ignition on, engine not running. With the DRBIII®, actuate the O2 Heater Test. With the DRBIII®, monitor O2 Sensor voltage for at least 2 minutes. Does the voltage stay above 4.5 volts? If yes, replace the O2 Sensor. If no, go to next step.
    8. NOTE: Throttle linkage must be moved very slowly while looking for a smooth change in voltage in this step.
  8. Ignition on, engine not running. With the DRBIII®, read TP Sensor voltage. The throttle must be against the stop. Is the voltage 0.92 of a volt or less with the Throttle closed? If yes, go to the next step. If no, check for a binding throttle condition. If OK, replace the Throttle Position Sensor.
  9. Turn ignition on, engine not running. 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.
  10. 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.
    11. 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).
  11. Turn ignition on, engine not running. With the DRBIII®, read the Engine Coolant Temperature 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 Engine Coolant Temperature value. The temperature value change should be a smooth transition from start up to normal operating temperature. The value should reach at least 180°F (82°C). Did the Engine Coolant Temperature increase smoothly and did it reach at least 180°F (82°C)? If yes, go to next step. If no, replace the Engine Coolant Temperature Sensor.
  12. Check for any of the following conditions/mechanical problems:
    • Air induction system must be free from leaks.
    • Engine vacuum must be at least 13 in. Hg in Neutral.
    • Engine valve timing must be within specification.
    • Engine compression must be within specification.
    • Engine exhaust system must be free of restrictions or leaks.
    • Engine Closed Crankcase Ventilation (CCV) system must flow freely.
    • Torque converter stall speed must be within specification.
    • Power brake booster must have no internal leaks.
    • Fuel must be free of contamination.
    • Fuel injectors must be free of restrictions.

    Are there any engine mechanical problems? If yes, repair as necessary. If no, go to INTERMITTENT CONDITION  under SELF-DIAGNOSTIC SYSTEM.

    13. NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test.
  13. Turn ignition on, engine not running. Disconnect the O2 Sensor harness connector. With the DRBIII®, monitor the O2 Sensor voltage. Is the O2 Sensor voltage above 4.5 volts? If yes, replace the O2 Sensor. If no, go to next step.
  14. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance between ground and the O2 Sensor Signal circuit at the PCM harness connector. Is the resistance below 100 ohms? If yes, repair the O2 Sensor Signal for a short to ground. If no, go to next step.
    15. NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
  15. Using the wiring diagram as a guide, inspect the wire harness and connectors. Pay particular attention to all power and ground circuits. If there are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
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