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Home >> Toyota >> 1996 >> Previa DX, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Tests W/Codes >> Circuit Tests >> DTC P0300 - Random Misfire Detected >> Diagnosis & Repair
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Diagnosis & Repair

  1. Inspect spark plug and check for spark at misfiring cylinder. See BASIC TESTING article. Repair as necessary. If spark plug is okay and spark is present, go to next step.
  2. Access ECM under driver's seat. Turn ignition on. Using DVOM, backprobe ECM connector. Measure voltage between ground and terminals No. 11 (Black/Blue wire) and No. 12 (Black wire) at ECM E8 connector. See Figure. If voltage is 9-14 volts for each circuit, go to step 4). If voltage is not 9-14 volts, go to next step.
  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 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 injector performance. 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 mechanical condition (compression, valve clearance, valve timing, etc.). See BASIC TESTING article.
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