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Diagnosis & Repair

WARNING: This page is about a different car, the 2000 Toyota Land Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
  1. If any other DTCs are displayed, diagnose and repair those DTCs first and retest. If only DTC P0125 is displayed, go to next step.
  2. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Start and warm engine to normal operating temperature. Using scan tool, monitor each heated oxygen sensor No. 1 output voltage. Snap accelerate engine to about 4000 RPM 3 times. Both heated oxygen sensors No. 1 should indicate a rich signal (.45 volt or more) at least once. If a rich signal is indicated for both heated oxygen sensors No. 1 at least once, go to step  9. If either heated oxygen sensor No. 1 does not display a rich signal at least once, go to next step.
  3. Check for open or short in wiring between appropriate heated oxygen sensor(s) No. 1 and ECM. If problem does not exist, go to next step. If problem exists, repair wiring as necessary. See WIRING DIAGRAMS article.
  4. Using scan tool, check if a misfire has occurred by monitoring DTCs and DATA LIST. If a misfire has occurred, perform DTC P0300: RANDOM MISFIRE DETECTED . If misfire has not occurred, 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 SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - V6 & V8 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 SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 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 heated oxygen sensor(s) No. 1.
  9. Perform test drive confirmation, then go to next step. See TEST DRIVE CONFIRMATION  under DTC P0130 OR P0150: HEATED OXYGEN SENSOR NO. 1 CIRCUIT.
  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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