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Home >> Lexus >> 2001 >> ES 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0171 Or P0172: System Too Lean/Rich (Bank No. 1) Or DTC P0174 Or P0175: System Too Lean/Rich (Bank No. 2) >> Diagnosis & Repair

Diagnosis & Repair

  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 fuel injectors. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If problem exists, repair as necessary. If problem does not exist, go to next step.
  3. Check Mass Airflow (MAF) meter and Engine Coolant Temperature (ECT) sensor. See ENGINE SENSORS & SWITCHES in appropriate SYSTEM & COMPONENT TESTING article. If problem exists, replace appropriate sensor(s). If problem does not exist, go to next step.
  4. Check spark and ignition system. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If problem exists, repair as necessary. If problem does not exist, go to next step.
  5. Check fuel pressure. See FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pressure is not within specification, repair as necessary. If fuel pressure is within specification, go to next step.
  6. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step.
  7. Connect scan tool to Data Link Connector (DLC) No. 3. Start engine and raise engine speed to 2500 RPM for approximately 90 seconds. Using scan tool, monitor each A/F sensor output voltage. See AIR/FUEL SENSOR OUTPUT VOLTAGE SPECIFICATIONS  table. If voltage is not as specified, go to next step. If voltage is as specified, go to step  9.
    AIR/FUEL SENSOR OUTPUT VOLTAGE SPECIFICATIONS

    Application & Operating Condition Specification
    Using OBD-II Scan Tool
    Engine Idling, Engine Racing & Driving Vehicle (1) (2)
    Using Lexus Scan Tool
    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.
  8. Check for open or short in wiring between ECM and A/F sensor. See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace A/F sensor.
  9. Using scan tool, clear DTCs. Perform test drive confirmation, then go to next step. See TEST DRIVE CONFIRMATION .
  10. Recheck for DTCs. If DTCs P0171, P0172, P0174 and/or P0175 are displayed again, replace ECM. If neither DTC P0171, P0172, P0174 and/or P0175 are displayed again, go to next step.
  11. Vehicle either ran out of fuel or problem is intermittent. Check component and ECM connections.
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