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Home >> Toyota >> 1995 >> Avalon XLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Testing >> Code 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 needed. 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 "E8". Measure voltage between ground terminal No. 34 (E01) and terminals No. 10, 9, 8, 7, 6, 5. See Figure. If voltage is NOT 9-14 volts, go to next step. If voltage is 9-14 volts for each circuit, go to step  4.
  3. Disconnect injector of misfiring cylinder. Using ohmmeter, measure resistance between injector terminals. If resistance is 13.4-14.2 ohms, inspect circuits between ECM and injector for open or short. See wiring diagram in WIRING DIAGRAMS article. Repair as needed. If resistance is NOT 13.4-14.2 ohms, replace injector.
  4. Inspect fuel pressure. See BASIC TESTING article. Repair as needed. If fuel pressure is okay, inspect fuel injector performance. See SYSTEM/COMPONENT TESTS article. Replace as needed.
  5. If all injectors are okay, inspect EGR system. See SYSTEM/COMPONENT TESTS article. Repair as needed. If EGR system is okay, inspect MAF sensor and CTS. See SYSTEM/COMPONENT TESTS article. Replace as needed. If both components are okay, also inspect engine compression, valve clearance and valve timing. See BASIC TESTING article.
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