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Home >> Lexus >> 2000 >> ES 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control >> Diagnosis & Repair

Diagnosis & Repair

  1. If other DTCs are displayed, diagnose and repair those DTCs first and retest system. If only DTC P0125 is displayed, go to next step.
  2. 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 RATIO SENSOR SPECIFICATIONS  table. If voltage is as specified, go to next step. If voltage is not as specified, go to step  9.
    AIR/FUEL RATIO SENSOR SPECIFICATIONS

    Application (1) Voltage
    Using OBD-II Scan Tool
    Engine Idling 0.66
    Engine Racing 0.76 Or More
    Driving Vehicle (2) 0.56 Or Less
    Using Lexus Scan Tool
    Engine Idling 3.3
    Engine Racing 3.8 Or More
    Driving Vehicle (2) 2.8 Or Less
    (1) Voltage should not remain at specification given.
    (2) Drive vehicle at 25 MPH or more with engine speed at 1500 RPM or more while opening and closing throttle valve.
  3. Check for open or short in wiring between ECM and suspect A/F sensor. See appropriate wiring diagram in WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, go to next step.
  4. Disconnect suspect A/F sensor harness connector. One A/F sensor is located in each exhaust manifold. Measure resistance between terminal B+ (Black wire) and HT (Black/White wire on bank No. 1 or Black/Red wire on bank No. 2) at A/F sensor connector (component side). Measure resistance at both A/F sensors. Resistance should be .8-1.4 ohms at 68°F (20°C) or 1.8-3.2 ohms at 1472°F (800°C). If resistance is not as specified, replace appropriate A/F sensor. If resistance is as specified, go to next step.
  5. 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.
  6. 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.
  7. 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.
  8. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, replace defective A/F sensor.
  9. Perform test drive confirmation then go to next step. See TEST DRIVE CONFIRMATION .
  10. Clear and recheck for DTCs. If DTC P0125 is displayed again, replace ECM. If DTC P0125 is not 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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