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Home >> Mazda >> 2002 >> MPV LX >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Random Misfire Detection >> Diagnostic Procedures
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Diagnostic Procedures

  1. Record freeze frame data. Check for service bulletins and on-line information. Repair as necessary. After repair, go to next step.
  2. Verify Related Pending Code Or Stored DTCs -  Turn ignition off, then on (engine off). Using scan tool, check for DTCs. If any other DTCs are present, repair those DTC(s) first. Refer to DIAGNOSTIC TROUBLE CODE IDENTIFICATION . If no other DTCs are present, go to next step.
  3. Verify Current Input Signal Status (Ignition Key To On/Idle) -  Using scan tool, access ECT, IAT, MAF, RPM, TP and VSS PIDs. Start engine and run at idle. Compare readings with specifications. See PIN VOLTAGE/PID VALUE CHARTS article. If all data is within specification, go to next step. If any data is not within specification, inspect suspected circuit or part. Refer to appropriate test in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. After repair, go to step  21.
  4. Verify Current Input Signal Status Under Trouble Condition -  Referring to FREEZE FRAME PID data, operate vehicle under same conditions as when DTC was set. Record PID data for RPM, TP, ECT, IAT, MAF and VSS. Compare readings with specifications. See PIN VOLTAGE/PID VALUE CHARTS article. If all data is within specification, go to next step. If any signal causes drastic changes, inspect suspected circuit and/or part. Refer to appropriate test in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. After repair, go to step  21.
  5. Inspect CMP Sensor -  Check CMP sensor. See CAMSHAFT POSITION SENSOR under SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If CMP sensor is okay, go to next step. If CMP sensor is faulty, check related components, including timing belt and gears. Replace faulty parts. If all related parts are okay, replace CMP sensor. After repair, go to step  21.
  6. Verify CKP Sensor Installation Condition -  Check CKP sensor mounting. If CKP sensor is tight, go to next step. If CKP sensor is loose, retighten sensor. After repair, go to step  21.
  7. Check Ignition Coil Operation With Spark Tester -  Start engine and allow to idle. Using spark tester, check for Bluish spark from each ignition coil. If any coil does not cause Bluish spark, go to next step. If all coils check okay, go to step  11.
  8. Check Secondary Ignition Coil Terminal Of No Spark Cylinder -  Turn ignition off. Check ignition coil for incorrect installation, damage or corrosion at ignition terminals, open lead and damaged cover. If no problem is found, go to next step. If any problem is found, replace faulty ignition coil. After repair, go to step  21.
  9. Inspect Power Supply Terminal At Ignition Coil Connector -  Disconnect ignition coil connector. Turn ignition on, engine off. Check voltage between ground and ignition coil harness connector terminal "A" (White/Violet wire). See appropriate wiring diagram under ENGINE PERFORMANCE in WIRING DIAGRAMS. If battery voltage is present, go to next step. If battery voltage is not present, repair open in White/Violet wire between ignition coil harness connector terminal "A" and ignition switch terminal "IG 1" (Blue wire). After repair, go to step  21.
  10. Inspect Ignition Coil Resistance -  Check ignition coil resistance. See IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If ignition coil is okay, go to step  21. If ignition coil is faulty, replace ignition coil. After repair, go to step  21.
  11. Inspect MAF PID -  Start engine. Using scan tool, access MAF PID. Depress accelerator pedal to WOT and release to race engine. MAF PID reading should respond quickly to RPM changes. If MAF PID reading responds as specified, go to next step. If MAF PID reading response is not as specified, replace MAF sensor. After repair, go to step  21.
  12. Inspect Excessive Air Suction In Intake Air System -  Check for vacuum leaks between MAF sensor and throttle body and between throttle body and dynamic chamber. If no leaks are present, go to next step. If any leaks are present, repair as necessary. After repair, go to step  21.
  13. Inspect Fuel Line Pressure -  Check fuel line pressure. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pressure is too low, go to next step. If fuel line pressure is too high, check fuel pump maximum pressure or for clogged fuel return hose. If no problem is found, replace fuel pressure regulator. After repair, go to step  21. If fuel line pressure is okay, go to step  17.
  14. Inspect Fuel Pump Maximum Pressure -  Check fuel pump maximum pressure. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pump maximum pressure is 86-116 psi (590-800 kPa), go to next step. If fuel pump maximum pressure is not as specified, inspect fuel pump circuit for open or poor connection. Repair as necessary. After repair, go to step  21. If no problem is present in fuel pump circuit, replace fuel pump. After repair, go to step  21.
  15. Inspect Fuel Line From Fuel Pump To Fuel Delivery Pipe  Check fuel line for leaks. If any leaks are present, replace fuel line. After repair, go to step  21. If leaks are not present, check fuel filters foreign material, restriction or clogging. If high pressure filter is clogged or restricted, replace high pressure fuel filter. If foreign material or stain is found in low pressure filter, clean fuel tank and filter. If no problem is found, replace fuel pressure regulator. Repair or replace as necessary. After repair, go to step  21.
  16. Inspect Engine Compression -  Check engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. If compression is okay, go to next step. If compression is low, overhaul engine. Refer to appropriate MECHANICAL article in ENGINES. After repair, go to step  21.
  17. Inspect Operation Of Purge Control Solenoid Valve -  Check purge control solenoid valve. See FUEL EVAPORATIVE SYSTEM (MPV) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If purge control solenoid valve operates as specified, go to next step. If purge control solenoid valve is faulty, replace purge control solenoid valve. After repair, go to step  21.
  18. Inspect PCV Valve Operation -  Check PCV valve operation. See POSITIVE CRANKCASE VENTILATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If PCV valve is okay, go to next step. If PCV valve is faulty, replace PCV valve. After repair, go to step  21.
  19. Inspect Operation Of EGR Valve -  Check EGR valve operation. Remove EGR valve. If EGR valve is okay, go to next step. If EGR valve is stuck open, replace EGR valve. After repair, go to step  21.
    WARNING: Removing radiator cap when radiator is hot is dangerous. Scalding coolant and steam may shoot out and cause serious injury. When removing radiator cap, wrap a thick cloth around and turn it slowly.
    NOTE: Large bubbles are normal since they are remaining air coming out from engine coolant passage.
  20. Inspect Sealing Of Engine Coolant Passage -  Check cooling system for combustion gasses. Remove radiator cap. Bleed air from cooling system. Start engine and let idle. Check for small bubbles which make coolant white at filler neck. If combustion gasses are not present, go to next step. If combustion gasses are present, repair or replace faulty parts as necessary. After repair, go to next step.
  21. Verify Trouble Shooting Of Misfire DTC Completed -  Turn ignition on, engine off. Using scan tool, clear DTC. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  under DRIVE MODES. Recheck DTC. If DTC P0300 is present, replace PCM. After repair, go to next step. If DTC P0300 is not present, go to next step.
  22. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If no other DTCs are present, testing is complete. If any other DTC is present, go to applicable test and repair.
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