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.
1		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.
2		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 ).
3		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.
4		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.
5		No	Go to the next step.
6	INSPECT CMP SENSOR Inspect the CMP sensor. (See CAMSHAFT POSITION (CMP) SENSOR INSPECTION ). Is there any malfunction?	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: Replace the CMP sensor. (See CAMSHAFT POSITION (CMP) SENSOR REMOVAL/INSTALLATION ). Go to Step 20.
6		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.
7		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.
8		No	Go to the next step.
9	INSPECT IGNITION SYSTEM OPERATION Perform the Spark Test. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION ). Is the strong blue spark visible at each cylinder?	Yes	Go to the next step.
9		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.
10		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.
11		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 Inspect the variable valve timing control system operation. (See ENGINE CONTROL SYSTEM OPERATION INSPECTION ). Does the variable valve timing control system work properly?	Yes	Go to the next step.
12		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.
13		No	Replace the purge solenoid valve, then go to Step 20. (See PURGE SOLENOID VALVE REMOVAL/INSTALLATION ).
14	INSPECT FUEL LINE PRESSURE Inspect the fuel line pressure. (See FUEL LINE PRESSURE INSPECTION ). Is the fuel line pressure normal?	Yes	Go to Step 16.
14		No	If the fuel line pressure is too low: Go to the next step. If the fuel line pressure is excess high: Replace the fuel pump unit, then go to Step 20. (See FUEL PUMP UNIT REMOVAL/INSTALLATION ).
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.
15		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: Replace the fuel pump unit. (See FUEL PUMP UNIT REMOVAL/INSTALLATION ). Go to Step 20.
16	INSPECT ENGINE COMPRESSION Inspect the engine compression. (See COMPRESSION INSPECTION ). Is there any malfunction?	Yes	Perform the engine overhaul for repairs, then go to Step 20.
16		No	Go to the next step.
17	INSPECT SEALING OF ENGINE COOLANT PASSAGE Perform the "ENGINE COOLANT LEAKAGE INSPECTION". (See ENGINE COOLANT LEAKAGE INSPECTION ). Is there any malfunction?	Yes	Repair or replace the malfunctioning part according to the inspection results, then go to Step 20.
17		No	Go to the next step.
18	INSPECT EGR VALVE OPERATION Remove the EGR valve. (See EGR VALVE REMOVAL/INSTALLATION ). Visually inspect the EGR valve for stuck to open. Is the EGR valve stuck to open?	Yes	Repair or replace the EGR valve, then go to Step 20. (See EGR VALVE REMOVAL/INSTALLATION ).
18		No	Go to the next step.
19	INSPECT PCV VALVE OPERATION Turn the ignition switch off. Inspect the PCV valve. (See POSITIVE CRANKCASE VENTILATION (PCV) VALVE INSPECTION ). Is the PCV valve operation normal?	Yes	Go to the next step.
19		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 ).
20		No	Go to the next step.
21	VERIFY AFTER REPAIR PROCEDURE Perform the "AFTER REPAIR PROCEDURE". (See AFTER REPAIR PROCEDURE ). Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE ).
21		No	DTC troubleshooting completed.