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Home >> Toyota >> 2003 >> Matrix Base, FWD, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 17 (Engine Control System Self-Diagnostics - V6) >> Diagnostic Tests >> DTC P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control >> Diagnosis & Repair
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Diagnosis & Repair

WARNING: This page is about a different car, the 2002 Toyota Tundra. 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 hose connections. PCV valve is located on top of passenger's side valve cover near front corner of valve cover. If PCV valve hose connections are okay, go to next step. If PCV valve hose connections are 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 maintain engine speed at 2500 RPM for about 90 seconds to fully warm the A/F sensor. Allow engine to idle.
  4. Using hand-held tester or scan tool, monitor A/F sensor output voltage with engine idling, engine racing and while driving vehicle at 25 MPH or more with engine speed of 1500 RPM or more while opening and closing the throttle. Ensure A/F sensor output voltage is within specification. See AIR/FUEL SENSOR OUTPUT VOLTAGE SPECIFICATIONS  table. If A/F sensor output voltage is not within specification, go to next step. If A/F sensor output voltage is within specification, go to step  11.
    NOTE: If A/F sensor output voltage remains 3.30 volts (Toyota hand-held tester) or .66 volt (OBD-II scan tool) during all conditions, A/F sensor circuit may be open. If A/F sensor output voltage remains 3.80 volts or more (Toyota hand-held tester) or .76 volt or more (OBD-II scan tool) during all conditions, A/F sensor circuit may be shorted. If A/F sensor output voltage remains 2.80 volts or less (Toyota hand-held tester) or .56 volt or less (OBD-II scan tool) during all conditions, A/F sensor circuit may be shorted. During fuel enrichment, A/F sensor output voltage may be less than 2.8 volts (Toyota hand-held tester) or .56 volt (OBD-II scan tool) which is normal. During fuel cut, A/F sensor output voltage may be more than 3.8 volts (Toyota hand-held tester) or .76 volt (OBD-II scan tool) which is normal.
    AIR/FUEL SENSOR OUTPUT VOLTAGE SPECIFICATIONS

    Application & Operating Condition Specification
    Using OBD-II Scan Tool
    Engine Idling, Engine Racing & Driving Vehicle (1) (2)
    Using Toyota Hand-Held Tester
    Engine Idling, Engine Racing & Driving Vehicle (1) (3)
    (1) Drive vehicle at 25 MPH or more with engine speed of 1500 RPM or more while opening and closing the throttle.
    (2) Voltage should not remain at .56 volt or less, .66 volt, or .76 volt or more.
    (3) Voltage should not remain at 2.80 volts or less, 3.30 volts, or 3.80 volts or more.
  5. Check for open and short in wiring harness and electrical connectors between A/F sensor and ECM. See WIRING DIAGRAMS article. A/F sensor is located on exhaust pipe in front of catalytic converter. 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. Disconnect electrical connector for A/F sensor. Using ohmmeter, check resistance for heater on A/F sensor between +B and HT terminals on electrical connector for A/F sensor. See Fig 1. Resistance should be .8-1.4 ohms at 68°F (20°C) and 1.8-3.2 ohms at 1472°F (800°C). If resistance is within specification, go to next step. If resistance is not within specification, replace A/F sensor. See AIR/FUEL SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
    Fig 1: Testing Heater On A/F Sensor
    G99C08733Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  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. 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 (.21-.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 A/F sensor. See AIR/FUEL 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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