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DTC P0300

DTC P0300  Random misfire detected 
DETECTION CONDITION 
  • The PCM monitors the CKP sensor input signal interval time. The PCM calculates change of interval time for each cylinder. If change of interval time exceeds preprogrammed criteria, the PCM detects misfire in the corresponding cylinder. While the engine is running, the PCM counts number of misfires that occurred at 200 crankshaft revolutions  and 1, 000 crankshaft revolutions  and calculates misfire ratio for each crankshaft revolution. If the ratio exceeds the preprogrammed criteria, the PCM determines that a misfire, which can damage catalytic converter or affect emission performance, has occurred.

Diagnostic support note 
  • This is a continuous monitor (misfire).
  • The MIL illuminates if the PCM detects the misfire which affects emission performance in two consecutive drive cycles or in one drive cycle while the DTC for the same malfunction has been stored in the PCM.
  • The MIL flashes if the PCM detects the misfire which can damage the catalytic converter during the first drive cycle.
  • PENDING CODE is available if the PCM detects the misfire which affects emission performance during the first drive cycle.
  • FREEZE FRAME DATA (Mode 2/Mode 12) is available.
  • The DTC is stored in the PCM memory.
POSSIBLE CAUSE 
  • Erratic signal to PCM
    • APP sensor signal malfunction
    • ECT sensor signal malfunction
    • IAT sensor signal malfunction
    • MAF sensor signal malfunction
    • CKP sensor signal malfunction
    • TP sensor signal malfunction
    • VSS signal malfunction
  • CMP sensor malfunction
  • CKP sensor looseness
  • Ignition system malfunction
    • Ignition coil related wiring harness malfunction
    • Ignition coil malfunction
    • Spark plug malfunction
  • Excess air suction in intake air system (between MAF sensor and intake manifold)
    • Vacuum hoses damages or improper connection
    • Pipe malfunction
  • MAF sensor contamination
  • Improper operation of variable valve timing control system
  • Improper operation of purge solenoid valve
  • Fuel supply system malfunction or improper fuel line pressure
    • Fuel pressure regulator (built-in fuel pump unit) malfunction
    • Fuel leakage in fuel line
    • Fuel line clogged
    • Fuel filter clogged
    • Fuel pump unit malfunction
    • Fuel runout
  • Engine internal malfunction
    • Engine coolant leakage to combustion chamber
    • Insufficient compression
  • EGR valve malfunction
  • PCV valve malfunction
  • Poor quality fuel
  • PCM malfunction
DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1 VERIFY FREEZE FRAME DATA (MODE 12) AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED 
  • Have the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS (misfire related) been recorded?
 Yes Go to the next step.
No Record the FREEZE FRAME DATA (Mode 12) and DIAGNOSTIC MONITORING TEST RESULTS on the repair order, then go to the next step.
2 VERIFY RELATED SERVICE BULLETINS AVAILABILITY 
  • Verify related Service Bulletins availability.
  • Is any related Service Bulletins available?
 Yes Perform the repair or diagnosis according to the available Service Bulletins.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
3 VERIFY RELATED PENDING CODE AND STORED DTC 
  • Turn the ignition switch off then to the ON position (Engine off).
  • Verify related PENDING CODE and stored DTC.
  • Are any DTCs present?
 Yes Go to the applicable DTC troubleshooting.
(See DTC TABLE ).
No Go to the next step.
4 VERIFY CURRENT INPUT SIGNAL STATUS (KEY TO ON/IDLE) 
  • Access the following PIDs using the M-MDS:
    • APP1
    • APP2
    • ECT
    • IAT
    • MAF
    • RPM
    • TP REL
    • VSS
  • Is there any signal that is far out of specification when the ignition switch is turned to the ON position and the engine idles?

    (See PCM INSPECTION ).

 Yes Inspect the suspected circuit.
  • If the inspection results are normal:
    • Go to the next step.
  • If the inspection results are not normal:
    • Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
No Go to the next step.
5 VERIFY CURRENT INPUT SIGNAL STATUS UNDER FREEZE FRAME DATA (MODE 2) CONDITION 
CAUTION:
  • While performing this step, always operate the vehicle in a safe and lawful manner.
  • When the M-MDS is used to observe monitor system status while driving, be sure to have another technician with you, or record the data in the M-MDS using the PID/DATA MONITOR AND RECORD capturing function and inspect later.

  • Inspect the same PIDs as in Step 4 while simulating FREEZE FRAME DATA (Mode 2) condition.
  • Is there any signal which causes drastic changes?
 Yes Inspect the suspected circuit
  • If the inspection results are normal:
    • Go to the next step.
  • If the inspection results are not normal:
    • Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
No Go to the next step.
6 INSPECT CMP SENSOR 
 Yes Inspect the installation condition and damages on timing chain and gears.
If there is a malfunction:
  • Repair or replace the malfunctioning part according to the inspection results.

If it is normal:

Go to Step 20.
No Go to the next step.
7 VERIFY CKP SENSOR INSTALLATION CONDITION 
  • Inspect if the CKP sensor is loosely installed.
  • Is the CKP sensor installed securely?
 Yes Go to the next step.
No Retighten the CKP sensor, then go to Step 20.
8 INSPECT IGNITION COIL AND RELATED WIRING HARNESS 
  • Inspect the ignition coil and related wiring harness condition (intermittent open or short) for all cylinders.
  • Is there any malfunction?
 Yes Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
No Go to the next step.
9 INSPECT IGNITION SYSTEM OPERATION 
 Yes Go to the next step.
No Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
10 INSPECT MAF PID 
  • Start the engine.
  • Access the MAF PID using the M-MDS.
  • Race the engine and verify that the MAF PID changes quickly according to change in the engine speed.
  • Is the MAF PID response normal?
 Yes Go to Step 12.
No Go to the next step.
11 INSPECT EXCESSIVE AIR SUCTION IN INTAKE AIR SYSTEM 
  • Inspect for air leakage between the following:
    • MAF sensor and throttle body
    • Throttle body and intake manifold
    NOTE:
    • Engine speed may change when rust penetrating agent is stayed on the air suction area.
  • Is there air leakage?
 Yes Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
No Replace the MAF/IAT sensor, then go to Step 20.
(See MASS AIR FLOW (MAF)/INTAKE AIR TEMPERATURE (IAT) SENSOR REMOVAL/INSTALLATION ).
12 INSPECT VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION 
 Yes Go to the next step.
No Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
13 INSPECT PURGE SOLENOID VALVE OPERATION 
  • Turn the ignition switch off.
  • Connect the vacuum pump to purge solenoid valve and apply vacuum to solenoid.
  • Verify that the solenoid holds vacuum.
  • Turn the ignition switch to the ON position (Engine off).
  • Access the EVAPCP PID in SIMULATION TEST using the M-MDS.
  • Set the duty value to 100% for the EVAPCP PID.
  • Apply vacuum while turning solenoid from OFF to ON and simulating the EVAPCP PID with 100% duty value.
  • Verify that solenoid releases vacuum while solenoid is turned ON.
  • Is the purge solenoid valve operation normal?
 Yes Go to the next step.
No Replace the purge solenoid valve, then go to Step 20.
(See PURGE SOLENOID VALVE REMOVAL/INSTALLATION ).
14 INSPECT FUEL LINE PRESSURE 
 Yes Go to Step 16.
No If the fuel line pressure is too low:
  • Go to the next step.

If the fuel line pressure is excess high:
15 INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DISTRIBUTOR 
  • Visually inspect the fuel line for fuel leakage.
  • Is there any fuel leakage?
 Yes Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
No Inspect fuel filters for the foreign materials or stain inside fuel filter (low-pressure side).
Perform the following actions according to the inspection results:
  • If the foreign materials or stain is found inside fuel filter (low-pressure side):
    • Clean the fuel tank and filter (low-pressure side).
  • If normal:

Go to Step 20.
16 INSPECT ENGINE COMPRESSION 
 Yes Perform the engine overhaul for repairs, then go to Step 20.
No Go to the next step.
17 INSPECT SEALING OF ENGINE COOLANT PASSAGE 
 Yes Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
No Go to the next step.
18 INSPECT EGR VALVE OPERATION 
 Yes Repair or replace the EGR valve, then go to Step 20.
(See EGR VALVE REMOVAL/INSTALLATION ).
No Go to the next step.
19 INSPECT PCV VALVE OPERATION 
 Yes Go to the next step.
No Replace the PCV valve, then go to the next step.
20 VERIFY TROUBLESHOOTING OF MISFIRE DTC COMPLETED 
  • Make sure to reconnect all disconnected connectors.
  • Turn the ignition switch to the ON position (Engine off).
  • Clear the DTC from the PCM memory using the M-MDS.
  • Perform the KOER self test (using M-MDS) or Drive Mode 03 (PCM Adaptive Memory Production, EGR System, A/F Sensor Heater, HO2S Heater, A/F Sensor, HO2S, and TWC Repair Verification Drive Mode) (not using M-MDS).

    (See KOEO/KOER SELF TEST ).

    (See OBD-II DRIVE MODE ).

  • Is the PENDING CODE for this DTC present?
 Yes Replace the PCM, then go to the next step.
(See PCM REMOVAL/INSTALLATION ).
No Go to the next step.
21 VERIFY AFTER REPAIR PROCEDURE 
 Yes Go to the applicable DTC inspection.
(See DTC TABLE ).
No DTC troubleshooting completed.
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