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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.
  1. Using Toyota hand-held tester or scan tool, check for any other DTCs. If only DTC P0125 exists, go to next step. If other DTCs exist, diagnose and repair those DTCs first and retest.
  2. Check for any loose or defective PCV valve piping connections. PCV valve is located at front of driver's side valve cover, below oil fill cap. If PCV valve piping is okay, go to next step. If PCV valve piping is defective, repair or replace components as necessary.
  3. With Toyota hand-held tester or scan tool still connected to DLC No. 3, start engine and warm engine to normal operating temperature. Allow engine to idle.
  4. Using hand-held tester or scan tool, monitor output voltage for heated oxygen sensors on exhaust manifolds (bank No. 1 sensor No. 1 and bank No. 2 sensor No. 1) while quickly increasing engine speed to 4000 RPM 3 consecutive times. Output voltage should indicate a rich signal of .45 volt at least once. If output voltage is not within specification, go to next step. If output voltage is within specification, go to step  11.
  5. Check for open and short in wiring harness and electrical connectors between appropriate heated oxygen sensor on each exhaust manifold (bank No. 1 sensor No. 1 and bank No. 2 sensor No. 1) and ECM. See WIRING DIAGRAMS article. ECM is located behind glove box and heater duct. See Figure. If wiring harness and electrical connectors are okay, go to next step. If wiring harness or electrical connector is defective, repair as necessary.
  6. Using hand-held tester or scan tool, check if a misfire has occurred by monitoring DTCs and DATA LIST. If misfire has not occurred, go to next step. If a misfire has occurred, perform appropriate DTC test for misfire detected.
  7. Ensure engine oil dipstick, oil filler cap, PCV system and all other air induction system components are intact and operating properly. If problem does not exist, go to next step. If problem exists, repair as necessary.
  8. Check fuel pressure. See FUEL PRESSURE under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - V6 & V8 article. Fuel pressure should be 38-44 psi (2.7-3.1 kg/cm2 ) with engine idling and should remain at least 21 psi (1.5 kg/cm2 ) for a minimum of 5 minutes after engine is shut off. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, repair fuel system as necessary.
  9. Check operation of fuel injectors. See FUEL CONTROL under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - V6 & V8 article. Fuel injector volume should be 56-69 cc (.18-.23 oz.) within 15 seconds and difference in volume between each fuel injector should be less than 13 cc (.04 oz.). Fuel injectors should not leak more than one drop every 12 minutes. If fuel injectors are okay, go to next step. If fuel injectors are defective, replace fuel injectors as necessary.
  10. Check exhaust system for leaks. If no exhaust leak exists, replace appropriate heated oxygen sensor located on exhaust manifold. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article. If exhaust leak exists, repair exhaust system as necessary.
  11. Using Toyota hand-held tester or scan tool, clear DTCs from ECM. Perform test drive confirmation and then go to next step. See TEST DRIVE CONFIRMATION .
  12. Recheck for DTCs. If DTC P0125 does not exist, go to next step. If DTC P0125 exists, replace ECM. ECM is located behind glove box and heater duct. See Figure.
  13. Verify if vehicle ran out of fuel. If vehicle ran out of fuel, DTC P0125 was caused by the vehicle running out of fuel. If vehicle did not run out of fuel, problem is intermittent. Check for defective connections or intermittent problem in wiring. ECM is located behind glove box and heater duct. See Figure.
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