Mike's Workshop Manuals: Service manuals for every vehicle
Home >> Lexus >> 1998 >> LS 400 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> DTC P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control >> Diagnosis & Repair

Diagnosis & Repair

  1. 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, heated oxygen sensor No. 1 and bank No. 2, heated oxygen sensor No. 1. Snap accelerate engine 3 times to 4000 RPM. Heater oxygen sensors should indicate a rich signal (.45 volt or more) at least once.
  2. If a rich signal is indicated for both heated oxygen sensors, replace ECM and retest. If either heated oxygen sensor does not display a rich signal, check for misfire. See DTC P0300-P0308:  RANDOM MISFIRE DETECTED. If misfire is not detected, check for open or short circuit in wiring harness between ECM and suspect heater oxygen sensor. See appropriate wiring diagram in SYSTEM WIRING DIAGRAMS article. Repair as necessary. If wiring harness is okay, replace suspect heater oxygen sensor and retest.
scientia non olet · About Mike's Workshop Manuals