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Home › Mazda › 2003 › 6 i, Standard › Repair and Diagnosis › Engine Performance › System › Engine Controls [Self-Diagnostics 2.3L] › Diagnostic Tests › DTC P0300: Random Misfire Detection › Diagnostic Procedure

Diagnostic Procedure

  1. If FREEZE FRAME DATA has been recorded, go to next step. If FREEZE FRAME DATA has not been recorded, record FREEZE FRAME DATA. Go to next step.
  2. Verify Related Repair Information Availability -  Check for related Service Bulletins and/or on-line repair information availability. If any related repair information is available, perform repair or diagnosis according to available repair information. If vehicle is not repaired, go to next step. If related repair information is not available, go to next step.
  3. Verify Related Pending Code Or Stored DTCs -  Turn ignition off, then on (engine off). Verify related PENDING CODE or stored DTCs. If no other DTCs are present and a driveability concern is not present, go to next step. If no other DTCs are present and a driveability concern is present, go to step  9. If any other DTC is present, go to appropriate DTC trouble shooting procedure. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  4. Verify Current Input Signal Status (Ignition Key To On/Idle) -  Access APP1, APP2, ECT, IAT, MAF, RPM, TP_REL, and VSS PIDs using WDS or equivalent. Refer to PIN VOLTAGE & PID VALUE CHART INDEX in PIN VOLTAGE CHARTS article. If all signals are within specification when ignition is on and engine is running at idle, go to next step. If any signal is far out of specification when ignition is on and engine is running at idle, check suspected circuit and/or part according to inspection results. After repair, go to step  22.
  5. Verify Current Input Signal Status Under Trouble Condition -  Check same PIDs as in step  4 while simulating FREEZE FRAME DATA condition. If no signal is present which cause drastic changes, go to next step. If any signal is present which causes drastic changes, check suspected circuit and/or part according to inspection results. After repair, go to step  22.
  6. Inspect CMP Sensor -  Inspect CMP sensor. See CAMSHAFT POSITION SENSOR under ENGINE 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 installation condition and damage on timing belt and gears, repair faulty components. If okay, replace CMP sensor. After repair, go to step  22.
  7. Verify CKP Sensor Installation Condition -  Inspect for CKP sensor looseness. If CKP sensor is tight, go to next step. If CKP sensor is loose, retighten CKP sensor. After repair, go to step  22.
  8. Inspect Ignition Coil Operation & High-Tension Lead With Timing Light -  Verify blinking condition on each cylinder using timing light at idle. If any cylinders do not show blinking condition, go to next step. If all cylinders show blinking condition, go to step  12.
  9. Inspect High-Tension Leads Of No Blinking Cylinder -  Turn ignition off. Inspect high-tension leads for improper installation, corrosion on terminal, open lead and damaged cover. If condition of high-tension leads are okay, go to next step. If any high-tension leads are faulty, replace suspect high-tension lead(s). After repair, go to step  22.
  10. Inspect Power Supply Terminal At Ignition Coil Connector -  Disconnect ignition coil 3-pin harness connector. Turn ignition on, engine off. Measure voltage between ignition coil 3-pin harness connector terminal "B" (Black/White wire) and body ground. If battery voltage is present, go to next step. If battery voltage is not present, check for open circuit in Black/White wire between ignition coil 3-pin harness connector terminal "B" and ignition switch. Repair or replace wiring harness. After repair, go to step  22.
  11. Inspect Ignition Coil Resistance -  Check ignition coil resistance. Refer to COIL PACKS under IGNITION SYSTEM in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If ignition coil resistance reading is okay, go to step  22. If ignition coil resistance reading is not okay, replace ignition coil. After repair, go to step  22.
  12. Inspect MAF PID -  Start engine. Access MAF PID using WDS or equivalent. Verify MAF PID changes quickly according to racing of engine RPM. If MAF PID response is okay, go to next step. If MAF PID response is not okay, replace MAF/IAT sensor. After repair, go to step  22.
  13. Inspect Excessive Air Suction In Intake Air System -  Check for air leakage at following:
    • Between MAF/IAT sensor and throttle body
    • Between throttle body and intake manifold
    If air leakage is not present, go to next step. If any air leakage is present, repair or replace suspected part. After repair, go to step  22.
  14. Inspect Fuel Line Pressure -  Inspect fuel line pressure. Refer to FUEL PRESSURE (EXCEPT B2300, B3000, B4000 & TRIBUTE) under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel line pressure is too low, go to next step. If fuel line pressure is okay, go to step  16. If fuel line pressure is too high, replace fuel pump unit. After repair, go to step  22.
  15. Inspect Fuel Line From Fuel Pump To Fuel Delivery Pipe -  Visually check fuel line for any leakage. If any fuel leakage is present, replace suspected fuel line. After repair, go to step  22. If fuel leakage is not present, check low-pressure side fuel filter for foreign materials or stain inside fuel filter. If foreign material or stain is found inside low-pressure side fuel filter, clean out fuel tank and low-pressure side filter. If foreign material or stain is not found in low-pressure side fuel filter, replace fuel pump unit. After repair, go to step  22.
  16. Inspect Engine Compression -  Inspect engine compression. Refer to MECHANICAL INSPECTION in BASIC DIAGNOSTIC PROCEDURES article. If engine compression is okay, go to next step. If engine compression is not okay, perform engine overhaul for repairs. After repair, go to step  22.
  17. Inspect Variable Valve Timing Control System Operation -  Inspect variable valve timing control system operation. Refer to VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION INSPECTION  under SYSTEM TESTS. If variable valve timing control system is working properly, go to next step. If variable valve timing control system is not working properly, repair or replace malfunctioning part according to variable valve timing control system inspection results. After repair, go to step  22.
  18. Inspect Operation Of Purge Control Solenoid Valve -  Inspect purge control system operation. Refer to PURGE CONTROL SYSTEM INSPECTION  under SYSTEM TESTS. If purge control system is working properly, go to next step. If purge control system is not working properly, repair or replace malfunctioning part according to purge control system inspection results. After repair, go to step  22.
  19. Inspect PCV Valve Operation -  Turn ignition off. Remove PCV valve and inspect valve operation. Refer to POSITIVE CRANKCASE VENTILATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If PCV valve is operating properly, go to next step. If PCV valve is faulty, replace PCV valve. After repair, go to step  22.
  20. Inspect Operation Of EGR Valve -  Remove EGR valve. Visually inspect valve for sticking open. Refer to EXHAUST GAS RECIRCULATION SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - MAZDA6, MIATA, MPV, PROTEGE & PROTEGE5 article. If EGR valve is okay, go to next step. If EGR valve is stuck open, replace EGR valve. After repair, go to step  22.
    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 cap and turn it slowly.
    NOTE: If there are any small bubbles which make engine coolant white at filler opening, air is getting in from poor sealing to head gasket or other areas between combustion chamber and engine coolant passage. Large bubbles are normal since they are remaining air coming out from engine coolant passage.
  21. Inspect Sealing Of Engine Coolant Passage -  Remove radiator cap. Perform procedure to bleed air from engine coolant, then run engine at idle. If there are any small bubbles which make engine coolant white at filler opening, repair or replace faulty parts. After repair, go to next step. If small bubbles are not present, go to next step.
  22. Verify Trouble Shooting Of Misfire DTC Is Completed -  Make sure to reconnect all disconnected connectors. Clear DTC from PCM memory using WDS or equivalent. Turn ignition off. Start engine. Perform MODE 1 - PCM ADAPTIVE MEMORY PRODUCE DRIVE MODE  under DRIVE CYCLES. If PENDING CODE of same DTC is not present, go to next step. If PENDING CODE of same DTC is present, replace PCM. For PCM removal and installation, see POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION article. After repair, go to next step.
  23. Verify After Repair Procedure -  Using scan tool, perform After Repair Procedure. See AFTER REPAIR PROCEDURE . If any DTCs are present, go to appropriate DTC inspection. Refer to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present, trouble shooting is complete.
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