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Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
  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 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 SYSTEM & COMPONENT TESTING article. If problem exists, replace appropriate sensor(s). If problem does not exist, go to next step.
  4. Check engine coolant temperature sensor. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If problem exists, replace appropriate sensor(s). If problem does not exist, go to next step.
  5. 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.
  6. 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.
  7. Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, go to next step.
  8. Connect the OBD-II scan tool or hand-held tester to the DLC3. Warm up the A/F sensors (bank 1, 2 sensor 1) with the engine at 2,500 RPM for approximately 90 seconds. On hand-held tester, select the ENHANCED OBD2/SNAPSHOT/MANUAL SNAP SHOT/ ALL mode. With either tester, read the voltage of A/F sensors (bank 1, 2 sensor 1) on the screen of the OBD-II scan tool or hand-held tester when performing conditions outlined in next step.
    NOTE: The voltage of AFR(+) - E1 (-) or AFL(+) - E1 (-) terminals of ECM is fixed at 3.3 volts and the voltage of terminals AFR (-) - E 1 or AFL (-) - E 1 (-) is fixed at 3.0 volts.
  9. Under normal conditions, with engine idling or racing at approximately 2500 RPM, (when engine revolution is not suddenly changed) voltage value changes a little in the vicinity of 3.3 volts (0.660 volts on OBD-II scan tool) between approximately 3.1-3.5 volts. With engine RPM increased to approximately 4000 RPM temporarily, then decreased to idle speed with accelerator completely released, voltage value changes into 3.8 volts (0.76 volts with OBD-II scan tool) or more temporarily. See Figure. Under a malfunction condition, voltage value does not change at all. See Figure. If system does not operate correctly, go to next step. If system operates correctly, go to step  13.
    NOTE: Whenever the output voltage of the A/F sensors remains at approximately 3.3 volts (0.660 volts with OBD-II scan tool) under any conditions as well as the above conditions, the A/F sensors may have an open circuit. This will happen also when the A/F sensor heater has an open circuit. Whenever the output voltage of the A/F sensors remains at a certain value of approximately 3.8 volts (0.76 volts on OBD-II scan tool) or more, or 2.8 volts (0.56 volts on OBD-II scan tool) or less under any conditions as well as the above conditions, the A/F sensor may have a short circuit.
  10. Check for open or short in wiring between ECM and A/F sensor. See ENGINE PERFORMANCE in WIRING DIAGRAMS article in ELECTRICAL. If problem exists, repair wiring as necessary. If problem does not exist, replace A/F sensor.
  11. Perform test drive confirmation, then go to next step. See CONFIRMATION DRIVING PATTERN  under DTC P0134 & P0154.
    NOTE: If conditions in test drive confirmation procedure are not strictly followed, detection of malfunction will not be possible.
  12. Clear and recheck for DTCs. If DTCs P0171, P0172, P0174 and/or P0175 are displayed again, replace ECM. If neither DTC P0171 and P0172 are displayed again, vehicle either ran out of fuel or problem is intermittent. Check component and ECM connections.
    NOTE: Because Lexus scan tool has CHECK mode feature, two-trip detection logic is disabled and problem can be isolated in one test drive. OBD-II scan tool does not have this feature. Therefore, two test drives are necessary to confirm repairs.
  13. Perform confirmation driving pattern. See CONFIRMATION DRIVING PATTERN  under DTC P0134 & P0154. If DTC P0171, P0172, P0174 and/or P0175 are output again, go to next step. If DTCs are not output again, go to step  15.
  14. Replace A/F sensor (bank 1 and/or 2 sensor 1). If DTCs P0171, P0172, P0174 and/or P0175 are output again, check and replace ECM. If DTCs are not output again, go to next step.
  15. Check if vehicle ran out of fuel in the past. If so, DTCs are caused by running out of fuel. If vehicle did not run out of fuel in the past, check for intermittent problems.
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