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Home >> Toyota >> 1997 >> Tercel 2D Sedan, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Circuit Tests >> DTC P0171: System Too Lean (Fuel Trim), DTC P0172: System Too Rich (Fuel Trim) >> Diagnosis & Repair
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Diagnosis & Repair

  1. Check all air induction components. Repair as necessary. If air induction components are okay, connect scan tool. See Figure. Start engine and warm to normal operating temperature. Monitor heated oxygen sensor output voltage and short-term fuel trim.
  2. If scan tool indicates a lean condition (.6 volt or less, +20 trim) or rich condition (.4 volt or more, -20 trim), go to next step. If results are other than shown, see DTC P0130:  OXYGEN SENSOR CIRCUIT (SENSOR NO. 1) circuit test.
  3. Check fuel pressure. See BASIC TESTING article. Repair fuel pressure as necessary. If fuel pressure is okay, check fuel injectors. See SYSTEM/COMPONENT TESTS article. Replace injectors as necessary.
  4. If all injectors are okay, check Manifold Absolute Pressure (MAP) sensor and Engine Coolant Temperature (ECT) sensor. See SYSTEM/COMPONENT TESTS article. Replace MAP and/or ECT sensor as necessary. If both components are okay, check ignition system. See IGNITION CHECKS in BASIC TESTING article. Repair ignition system as necessary. If ignition system is okay, replace ECM and retest.
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