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Home >> Lexus >> 1996 >> ES 300 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0300 - Random Misfire Detected >> Diagnosis & Repair
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Diagnosis & Repair

  1. Inspect spark plugs and ignition system. See BASIC TESTING article. Repair as necessary. If ignition system is okay, ensure ignition is off.
  2. Access ECM harness connectors behind glove box. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between ground and injector terminals at ECM E7 connector. See IDENTIFYING INJECTOR TERMINALS  table. If voltage is 9-14 volts for each circuit, go to step 4). If voltage is not 9-14 volts, go to next step.
    IDENTIFYING INJECTOR TERMINALS

    Injector No. (1) Terminal No. Wire Color
    1 10 White
    2 9 Yellow
    3 8 Gray
    4 7 Blue
    5 6 Red
    6 5 Green
    (1) Terminals are located in ECM E7 connector.
  3. Disconnect injector of misfiring cylinder. Using ohmmeter, measure resistance between injector terminals. With injector temperature at 68°F (20°C), if resistance is 13.4-14.2 ohms, inspect circuits between ECM and injector for open or short circuit. See appropriate wiring diagram in WIRING DIAGRAMS article. Repair as necessary. If resistance is not 13.4-14.2 ohms, replace injector.
  4. Check fuel pressure. See BASIC TESTING article. Repair as necessary. If fuel pressure is okay, inspect fuel injectors. See SYSTEM/COMPONENT TESTS article. Replace as necessary.
  5. If all injectors are okay, inspect EGR system. See SYSTEM/COMPONENT TESTS article. Repair as necessary. If EGR system is okay, inspect MAF sensor and ECT sensor. See SYSTEM/COMPONENT TESTS article. Replace as necessary. If both components are okay, check engine compression, valve clearance and valve timing. See BASIC TESTING article. Repair as necessary.
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