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Home >> Mazda >> 2003 >> Protege ES, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0300: Random Misfire Detected >> Diagnostic Procedure

Diagnostic Procedure

  1. Verify Related Repair Information Availability -  Turn ignition off. Connect scan tool to DLC-2. Turn ignition on, engine off. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to next step.
  2. Verify Related Pending Code & Stored DTCs -  Turn ignition off, then start engine. Using scan tool, check for pending code or related DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If no other DTCs are present, go to next step. If DTCs are present, go to appropriate trouble shooting procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  3. Verify Current Input Signal Status (Ignition Key To On/Idle) -  Using scan tool, access ECT, IAT, MAF, RPM, TP and VS PIDs. Start engine and run at idle. Ensure all signal data is within specification. See PIN VOLTAGE CHARTS article. If all PID data is within specification, go to next step. If any PID data is not within specification, go to applicable test in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. After repair, go to step  22.
  4. Verify Current Input Signal Status Under Trouble Condition -  Monitor ECT, IAT, MAF, RPM, TP and VS PIDs while simulating FREEZE FRAME DATA condition. If no drastic changes occur to any signals, go to next step. If any signal is drastically changed, go to applicable test in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. Diagnose and repair as necessary. After repair, go to step  22.
  5. Inspect CMP Sensor -  Check CMP sensor operation. See BASIC DIAGNOSTIC PROCEDURES article. If CMP sensor is operating properly, go to next step. If CMP sensor is not operating properly, ensure CMP sensor is installed correctly, and timing belt and gears are not damaged before replacing CMP sensor. After repair, go to step  22.
  6. Verify CKP Sensor Installation Condition -  Check CKP sensor installation. See CRANKSHAFT POSITION SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL OVERHAUL & INSTALLATION article. If CKP sensor is loose or incorrectly installed, reinstall CKP sensor. After repair, go to step  22. If CKP sensor is not loose, go to next step.
  7. Check Ignition Coil Operation And High-Tension Lead With Timing Light -  Start engine and allow to idle. Check ignition coil operation at each cylinder with timing light. If timing light flashes at all cylinders, go to step  11. If timing light does not flash as specified, go to next step.
  8. Check High-Tension Leads Of Non- Blinking Cylinder -  Turn ignition off. Inspect high-tension lead condition, corrosion on terminal, open lead and damaged cover. If condition of high-tension lead is okay, go to next step. If condition of high tension lead is faulty, replace high tension lead. After repair, go to step  22.
  9. Inspect Power Supply Terminal At Ignition Coil Connector -  Disconnect ignition coil 3-pin harness connector. Turn ignition on, engine off. Measure voltage between ground and ignition coil 3-pin harness connector terminal "A" (Black/Blue wire). If battery voltage is present, go to next step. If battery voltage is not present, repair open circuit in Black/Blue wire between ignition switch terminal "IG1" and ignition coil 3-pin harness connector terminal "A". See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  22.
  10. Inspect Ignition Coil Resistance -  Check ignition coil resistance. See EXCEPT B2300, B3000, B4000 & TRIBUTE under IGNITION CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If ignition coil is okay, go to step  22. If ignition coil is faulty, replace ignition coil. After repair, go to step  22.
  11. Inspect MAF Signal -  Start engine. Using scan tool, access MAF PID. Depress accelerator pedal to Wide Open Throttle (WOT) and release to race engine. MAF PID voltage reading should respond quickly with engine RPM. If MAF PID response is as specified, go to next step. If MAF PID response is not as specified, replace MAF sensor. After repair, go to step  22.
  12. Inspect Excessive Air Suction In Intake-Air System -  Check for vacuum leaks in intake-air system between MAF sensor and throttle body. Also check for vacuum leaks at throttle body and dynamic chamber. If vacuum leak is detected, repair or replace as necessary. After repair, go to step  22. If no problem is found, go to next step.
  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 line pressure is okay, go to step  17. If fuel line pressure is too high, go to next step. If fuel line pressure is too low, go to step  15.
  14. Verify Vacuum Leading To Pressure Regulator -  Disconnect vacuum hose from fuel pressure regulator. Start engine. If vacuum is present at end of vacuum hose, check fuel pump maximum pressure. See FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Check fuel return hose for clogging or restriction. If no problems are found, replace fuel pressure regulator. If any problems are found, repair or replace fuel return hose. After repair, go to step  22. If no vacuum is present at end of vacuum hose, check vacuum hose routing. If hoses are okay, replace Pressure Regulator Control (PRC) solenoid valve. If vacuum hoses are misrouted, reinstall correctly. Repair as necessary. After repair, go to step  22.
  15. 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 maximum fuel pump pressure is 64-92 psi (4.5-6.5 kg/cm2 ), go to next step. If maximum fuel pump pressure is not as specified, repair open circuit or poor connection in fuel pump circuit. If fuel pump circuit is okay, replace fuel pump. After repair, go to step  22.
  16. Inspect Fuel Line From Fuel Pump To Fuel Delivery Pipe -  Check for leaks in fuel system. If any leaks are found, replace suspected fuel line. After repair, go to step  22. If no leaks are found, check for restriction at high pressure fuel filter and foreign material or stain inside low pressure fuel filter. If restriction is present at high pressure fuel filter, replace high pressure fuel filter. If foreign material or stain is found inside low pressure fuel filter, clean fuel tank and low pressure fuel filter. If fuel filters and fuel tank are okay, replace fuel pressure regulator. Repair as necessary. After repair, go to step  22.
  17. Inspect Engine Compression -  Check engine compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. If engine compression is as specified, go to next step. If engine compression is not as specified, repair as necessary. After repair, go to step  22.
    NOTE: Purge solenoid valve may also be referred to purge control solenoid valve.
  18. Inspect Operation Of Purge Solenoid Valve -  Check purge solenoid valve. See FUEL EVAPORATIVE SYSTEM (EXCEPT MIATA & MPV) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If purge solenoid valve is okay, go to next step. If purge solenoid valve is faulty, replace purge solenoid valve. After repair, go to step  22.
  19. 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 faulty, replace PCV valve. After repair, go to next step. If PCV valve is okay, go to step  22.
  20. Inspect Operation Of EGR Valve -  Remove EGR valve and ensure valve is not stuck open. If no problem is found, reinstall EGR valve and go to next step. If EGR valve is stuck open, replace or repair EGR valve as necessary. After repair, go to step  22.
  21. 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 leak as necessary. After repair, go to next step.
  22. Verify Trouble Shooting Of Misfire DTC Completed -  Reconnect all connectors. Turn ignition on, engine off. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine. Using scan tool, perform MODE 1 - PCM ADAPTIVE MEMORY PROCEDURE DRIVE MODE  under SELF-DIAGNOSTIC SYSTEM. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P0300 is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION article. After repair, go to next step. If same DTC P0300 is not present, go to next step.
  23. 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, follow appropriate DTC diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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