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DTC P0300 - Random Misfire Detected

NOTE: For terminal identification, see TERMINAL IDENTIFICATION in SELF-DIAGNOSTICS section. For circuit and wire color identification, see WIRING DIAGRAMS article.
  1. Connect external tachometer. Using scan tool in MUT II mode, read SERVICE DATA No. 22 (crankshaft position sensor). Check engine RPM during cranking and at idle. If RPM displayed on scan tool and tachometer are equal, go to next step. If RPM displayed on scan tool and tachometer are not equal, go to step 4).
  2. Using oscilloscope, perform crankshaft position sensor wave form check. Connect Test Harness (MD991348) between Crankshaft Position (CKP) sensor and harness connector. Connect analyzer special patterns pickup to CKP sensor terminal No. 2. If test harness is not available, connect analyzer special patterns pickup to PCM terminal No. 89. Go to next step.
  3. With engine idle speed stable, compare CKP sensor wave pattern to known-good wave pattern. See Fig 1 . If wave pattern is okay, go to step 5). If wave pattern is not okay, go to next step.
    Fig 1: Identifying Known-Good CKP Sensor Wave Pattern
    G93A80275Courtesy of MITSUBISHI MOTOR SALES OF AMERICA
  4. Check CKP sensor connector, PCM connector and wiring harness between PCM and CKP sensor connector. Check CKP sensor and sensing plate for proper installation. If wiring, connectors and sensor installation are okay, replace CKP sensor.
  5. Disconnect fuel injector connector. Check resistance across fuel injector terminals. If resistance at 68°F (20°C) is 13-16 ohms, go to next step. If resistance is not as specified, replace fuel injector.
  6. Using stethoscope, check injector operating sound during cranking or at idle. Check that frequency of operating sound increases as engine RPM increases. If injectors are okay, go to next step. If no operating sound is heard from an injector, check injector drive circuit. If drive circuit is okay, injector or PCM is suspect.
  7. Check fuel injector connectors, PCM connector and wiring harness between PCM and injector connectors. If wiring and connectors are okay, go to next step.
  8. Disconnect fuel injector connectors. Turn ignition on. Check voltage between ground and each injector connector terminal No. 1. If battery voltage exists at all connectors, go to next step. If battery voltage does not exist at any one or all connectors, check connectors and wiring harness between PCM and fuel injector connectors.
  9. Connect fuel injector connectors. Disconnect PCM connector. Turn ignition on. Check voltage between ground and PCM connector terminals No. 1, 2, 14 and 15. Also check voltage between ground and PCM connector terminals No. 3 and 16. On all models, if battery voltage exists at all terminals, check PCM connector. If PCM connector is okay, go to next step. If battery voltage does not exist at any one or all terminals, check fuel injector connectors and wiring harness between PCM and injector connector.
  10. Start and warm engine. Turn all accessories off. Increase engine speed to 2500 RPM. Using scan tool in MUT II mode, read SERVICE DATA No. 81 (long-term fuel compensation). If fuel trim is -12.5-12.5 percent (during closed loop), go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0170: FUEL TRIM MALFUNCTION.
  11. Using scan tool in MUT II mode, read SERVICE DATA No. 82 (short-term fuel compensation). If fuel trim is -20.0-20.0 percent, go to next step. If fuel trim is not as specified, check fuel trim fault. See DTC P0170: FUEL TRIM MALFUNCTION.
  12. Using scan tool in MUT II mode, read SERVICE DATA No. 21 (engine coolant temperature). If temperature displayed on scan tool is equal to actual engine coolant temperature, go to next step. If temperature displayed on scan tool is not equal to actual engine coolant temperature, check ECT circuit. See DTC P0115: ENGINE COOLANT TEMPERATURE (ECT) CIRCUIT MALFUNCTION.
  13. Check ignition coil, spark plugs and spark plug wires. Check compression pressure. See BASIC TESTING article.
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