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Home >> Lexus >> 2001 >> IS 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0171 Or P0172: System Too Lean/Rich (Bank No. 1) DTC P0174 Or P0175: System Too Lean/Rich (Bank No. 2) >> Diagnosis & Repair

Diagnosis & Repair

  1. 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.
  2. 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.
  3. Check Mass Airflow (MAF) meter and Engine Coolant Temperature (ECT) sensor. See ENGINE SENSORS & SWITCHES in appropriate SYSTEM & COMPONENT TESTING article. If problem exists, replace appropriate sensor(s). If problem does not exist, go to next step.
  4. Check spark and ignition system. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If problem exists, repair as necessary. If problem does not exist, go to next step.
  5. 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.
  6. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step.
  7. Connect scan tool to Data Link Connector (DLC) No. 3. Start engine and raise engine speed to 2500 RPM for approximately 90 seconds. Let engine idle. Using scan tool, monitor each No. 1 heated oxygen sensor's output voltage. Voltage should alternate repeatedly between less than .4 volt to more than .55 volt. If voltage is as specified, go to step  9. If voltage is not as specified, go to next step.
  8. Check for open or short in wiring between ECM and heated oxygen sensor No. 1. See WIRING DIAGRAMS article. If problem exists, repair wiring as necessary. If problem does not exist, replace appropriate No. 1 heated oxygen sensor(s).
  9. Perform test drive confirmation, then go to next step. See TEST DRIVE CONFIRMATION .
  10. Clear and recheck for DTCs. If DTCs P0171, P0172, P0174 or P0175 are displayed again, replace ECM. If DTCs P0171, P0172, P0174 or P0175 are not displayed again, go to next step.
  11. Vehicle either ran out of fuel or problem is intermittent. Check component and ECM connections.
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