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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 P0171: System Too Lean, Or P0172: System Too Rich >> 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. 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.
  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. 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.
  4. Check Mass Airflow (MAF) meter and Engine Coolant Temperature (ECT) sensor. MAF meter may also be referred to as airflow meter. See AIRFLOW METER and ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - V6 & V8 article. If MAF meter and ECT sensor are okay, go to next step. If MAF meter or ECT sensor is defective, replace components as necessary. See AIRFLOW METER or ENGINE COOLANT TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
  5. Check ignition system by performing spark test. See SPARK TEST under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - V6 & V8 article. If ignition system operates properly and spark exist, go to next step. If ignition system does not operate properly and spark does not exist, repair ignition system as necessary.
  6. 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.
  7. Check exhaust system for leaks. If no exhaust leak exists, go to next step. If exhaust leak exists, repair exhaust system as necessary.
  8. Connect Toyota hand-held tester or scan tool to Data Link Connector (DLC) No. 3 at driver's side of instrument panel. See Figure. Start engine and maintain engine speed at 2500 RPM for about 90 seconds to fully warm the A/F sensor. Allow engine to idle.
    9. NOTE: ECM maintains a fixed voltage of 3.3 volts at AF1+ terminal on ECM and 3.0 volts at AF1- terminal on ECM. It is impossible to confirm A/F sensor output voltage without using Toyota hand-held tester or scan tool. A/F sensor output voltage on scan tool is displayed at one fifth the voltage of that displayed on a Toyota hand-held tester.
    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.
  9. 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 as specified. 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.
    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.
  10. 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, replace A/F sensor. See AIR/FUEL SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article. If wiring harness or electrical connector is defective, repair 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 P0171 or P0172 does not exist, go to next step. If DTC P0171 and/or P0172 exist, 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 P0171 and/or P0172 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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