LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lexus >> 2000 >> SC 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control >> Diagnosis & Repair
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair

  1. Retrieve trouble codes. See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. If any other codes are displayed other than DTC P0125, diagnose and repair those codes first. If only DTC P0125 is displayed, go to next step.
  2. Connect scan tool to Data Link Connector (DLC) No. 3. See Figure. Start engine and warm to normal operating temperature. Using scan tool, monitor bank No. 1, sensor No. 1 and bank No. 2, sensor No. 1. Snap accelerate engine 3 times to 4000 RPM. Sensors should indicate a rich signal (.45 volt or more) at least once. If a rich signal is indicated for both sensors, go to step  9. If either sensor does not display a rich signal, go to next step.
  3. Check for open or short circuit in wiring harness between ECM and suspect oxygen sensor. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair wiring as necessary. If wiring harness is okay, go to next step.
  4. Check for misfire. See DTC P0300: RANDOM CYLINDER MISFIRE DETECTED . If misfire is not detected, check for exhaust leaks. If exhaust leaks are not detected, replace oxygen sensor and retest.
  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 heated oxygen 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.
scientia non olet · About LEMON Manuals