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Home >> Dodge and Ram >> 2003 >> Durango Base, 5.9 Z, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 15 (Engine Controls - Self Diagnostics - 4.7L) >> Diagnostic Tests >> DTC P0171: Fuel System 1/1 Lean & DTC P0174: Fuel System 2/1 Lean >> Testing

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

WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.
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.
NOTE: Before proceeding, check for contaminants that may have damaged HO2S such as contaminated fuel, unapproved silicone, oil and coolant.
NOTE: Diagnose any and all other DTCs first, if set along with the fuel system DTC.
  1. Ignition on, engine not running. With the DRBIII® scan tool, read DTCs and record the related freeze frame data. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, see INTERMITTENT CONDITION  under SELF-DIAGNOSTIC SYSTEM.
    2. 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. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE .
  2. Install a fuel pressure gauge. Ignition on, engine not running. With the DRBIII® scan tool, actuate ASD fuel system test and observe fuel pressure gauge. Fuel pressure should be 44-54 psi (304-373 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 above specification, stop all actuations and replace the fuel filter/pressure regulator.
    3. NOTE: If one of the O2 sensors signal or return circuit is shorted to ground the DRBIII® scan tool will display all O2 sensor voltage readings low. The O2 sensor that is shorted to ground will display a voltage reading near or at 0 volts. If one of the 02 sensors signal or return circuit is shorted to voltage, the DRBIII® scan tool will display all O2 sensor voltage readings high. It is important to diagnose the O2 sensor that set the DTC. After the repairs have been made, verify proper O2 sensor operation. If all the O2 sensor voltage readings have not returned to normal, follow the diagnostic procedure for the remaining O2 sensors.
  3. Start the engine. Allow the engine to reach normal operating temperature. With the DRBIII® scan tool, read the O2 sensor voltage. Is the voltage switching between 2.5 volts and 3.4 volts for all of the O2 sensors? If yes, go to next step. If no, go to step  10.
  4. Turn the ignition off. Allow the O2 sensor to cool down before continuing the test. Allow the O2 sensor voltage to stabilize at 5.0 volts. Ignition on, engine not running. With the DRBIII® scan tool, actuate the O2 heater test. With the DRBIII® scan tool, 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.
  5. With the DRBIII® scan tool, 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 OK, replace the throttle position sensor.
  6. With the DRBIII® scan tool, read TP sensor voltage. While monitoring the DRBIII® scan tool, slowly open and close the throttle. Does the voltage increase and decease smoothly? If yes, go to next step. If no, replace the TP 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® scan tool in sensors, read the MAP sensor vacuum value. Is the DRBIII® scan tool 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). Ignition on, engine not running. With the DRBIII® scan tool, 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 ECT value increase a smooth transition 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 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. NOTE: Perform the following test on all O2 sensors.
    NOTE: Remove the jumper wire before continuing.
  10. Ignition on, engine not running. Disconnect the O2 sensor harness connector. With the DRBIII® scan tool, monitor the O2 sensor voltage. The O2 sensor voltage should read 5.0 volts on the DRBIII® scan tool with the connector disconnected. Using a jumper wire, jump across the O2 sensor harness connector from the O2 signal circuit to the O2 return circuit at the O2 sensor harness connector. The voltage should drop from 5.0 volts to 2.5 volts with the jumper wire in place. Did the O2 sensor volts change from 5.0 volts to 2.5 volts? If yes, replace the O2 sensor. If no, go to next step.
  11. Disconnect one sensor at a time. With the DRBIII® scan tool, monitor the O2 sensor voltages. The DRBIII® scan tool will display all O2 sensor voltage readings approximately 5.0 volts when only one O2 sensor's signal circuit is shorted to voltage. The DRBIII® scan tool will display one O2 sensor voltage close to zero and the others will read lower than normal when the O2 sensor signal circuit has excessive resistance or is the voltage above 4.8 volts? If yes, go to next step. If no, check all the O2 signal circuit's for a short to ground, open, or short to voltage. Inspect the O2 sensor connector and the PCM harness connector. If OK, replace and program the PCM. See PROGRAMMING .
  12. Disconnect each O2 sensor harness connector. Measure the voltage on the O2 return circuit in the O2 sensor harness connector. The DRBIII® scan tool will display all O2 sensor voltage readings approximately 5.0 volts when only one O2 sensor's return circuit is shorted to voltage. The DRBIII® scan tool will display one O2 sensor voltage close to zero and the others will read lower than normal when the O2 sensor return circuit has excessive resistance or is open. Is the voltage at 2.5 volts? If yes, replace and program the PCM. See PROGRAMMING . If no, check all the O2 return circuits for a short to ground, open, or short to voltage. Inspect the O2 sensor connector and the PCM harness connector. If OK, replace and program the 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, engine not running. With the DRBIII® scan tool, 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. Stop all actuations. If fuel pressure is 54-64 psi (305-373 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. 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. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE .
  14. Turn ignition off. 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.
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