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Home >> Toyota >> 2001 >> Sienna CE >> Repair and Diagnosis >> External Pages >> Different car >> Section 17 (Engine Control System Self-Diagnostics - 4-Cylinder) >> Diagnostic Tests >> DTC P0171, DTC P0172, DTC P0174 Or DTC P0175: System Too Lean/Rich >> Diagnosis & Repair

Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Toyota Highlander. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ensure oil dipstick, oil filler cap, PCV system and all other air induction system components are intact and operating properly. If problem exists, repair as necessary. If problem does not exist, go to next step.
  2. Check operation of fuel injectors. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. Fuel injector volume should be 4.2-5.0 Cu. In. (69-82 cc) every 15 seconds and difference in volume between each fuel injector should be less than .8 Cu. In. (13 cc). Fuel injectors should not leak more than one drop every 12 minutes. If problem does not exist, go to next step. If problem exists, repair as necessary.
  3. Check Mass Airflow (MAF) meter and Engine Coolant Temperature (ECT) sensor. MAF meter may also be referred to as airflow meter. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If problem does not exist, go to next step. If problem exists, replace appropriate component.
  4. Check ignition system by performing spark test. See IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4-CYLINDER article. If problem does not exist, go to next step. If problem exists, repair as necessary.
  5. Check fuel pressure. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4-CYLINDER article. Fuel pressure should be 44-50 psi (3.1-3.5 kg/cm2 ) at idle, and should be 21 psi (1.5 kg/cm2 ) or more for 5 minutes after engine has stopped. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, repair as necessary.
  6. Check exhaust system for leaks. If problem does not exist, go to next step. If problem exists, repair as necessary.
  7. Connect Toyota hand-held tester or scan tool to Data Link Connector (DLC) No. 3. See Figure. Start engine and increase engine speed to 2500 RPM for approximately 90 seconds to fully warm the A/F sensor. Allow engine to idle.
    8. NOTE: ECM maintains a fixed voltage of 3.3 volts at AF1A+ and AF2A+ terminals on ECM, and 3.0 volts at AF1A- and AF2A- terminal on ECM. It is impossible to confirm A/F sensor output voltage without using Toyota hand-held tester or scan tool. A/F sensor output voltage on scan tool is displayed at one fifth the voltage of that displayed on a Toyota hand-held tester.
    NOTE: If A/F sensor output voltage remains 3.30 volts (Toyota hand-held tester) or .66 volt (OBD-II scan tool) during all conditions, A/F sensor circuit may be open. If A/F sensor output voltage remains 3.80 volts or more (Toyota hand-held tester) or .76 volt or more (OBD-II scan tool) during all conditions, A/F sensor circuit may be shorted. If A/F sensor output voltage remains 2.80 volts or less (Toyota hand-held tester) or .56 volt or less (OBD-II scan tool) during all conditions, A/F sensor circuit may be shorted. During fuel enrichment, A/F sensor output voltage may be less than 2.8 volts (Toyota hand-held tester) or .56 volt (OBD-II scan tool) which is normal. During fuel cut, A/F sensor output voltage may be more than 3.8 volts (Toyota hand-held tester) or .76 volt (OBD-II scan tool) which is normal.
  8. Using hand-held tester or scan tool, monitor each A/F sensor output voltage with engine idling, engine racing and while driving vehicle at 25 MPH or more with engine speed at 1500 RPM or more while opening and closing the throttle. Ensure A/F sensor output voltage is as specified. See AIR/FUEL SENSOR OUTPUT VOLTAGE SPECIFICATIONS  table. If A/F sensor output voltage is not within specification, go to next step. If A/F sensor output voltage is within specification, go to step  10.
    AIR/FUEL SENSOR OUTPUT VOLTAGE SPECIFICATIONS

    Application & Operating Condition Specification
    Using OBD-II Scan Tool
    Engine Idling, Engine Racing & Driving Vehicle (1) (2)
    Using Toyota Hand-Held Tester
    Engine Idling, Engine Racing & Driving Vehicle (1) (3)
    (1) Drive vehicle at 25 MPH or more with engine speed of 1500 RPM or more while opening and closing the throttle.
    (2) Voltage should not remain at .56 volt or less, .66 volt, or .76 volt or more.
    (3) Voltage should not remain at 2.80 volts or less, 3.30 volts, or 3.80 volts or more.
  9. Check for open or short in wiring between ECM and A/F sensor(s). See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace appropriate A/F sensor.
  10. Using Toyota hand-held tester or scan tool, clear DTCs from ECM. Perform test drive confirmation, then go to next step. See TEST DRIVE CONFIRMATION  under DTC P1130 OR DTC P1150: AIR/FUEL SENSOR CIRCUIT RANGE/PERFORMANCE.
  11. Recheck for DTCs. If DTC P0171, DTC P0172, DTC P0174 and/or DTC P0175 are displayed again, go to next step. If DTCs P0171, DTC P0172, DTC P0174 and/or DTC P0175 are displayed again, replace ECM.
  12. Vehicle either ran out of fuel or problem is intermittent. Check component and ECM connections.
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