P0300
P0300Component Location:
General Description
Misfires can be caused by lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or many other causes. Even a small number of misfires may result in excessive exhaust emissions due to the unburned mixture. Increased misfire rates cause damage to the catalytic converter. The PCM monitors the crankshaft speed variation to determine if any misfiring generated. The PCM identifies the specific cylinder in which the misfire has occurred and counts individual misfire events by monitoring changes in the crankshaft rotation for each cylinder. A random misfire indicates two or more cylinders are misfiring.
DTC Description
The misfire diagnostic measures reference event times and calculates the positive and negative acceleration of the crank wheel to determine whether a misfire has occurred.
When the rate of misfire exceeds a threshold where the catalyst reaches a temperature where permanent damage can occur, to the point that tail pipe emissions reach 1.5 times the tailpipe standard or where a cylinder misfire cause a loss of torque produced from that cylinder. PCM sets this DTC. In case that misfire affects Catalyst damage, MIL(Malfunction Indication Lamp) will be illuminating and blinking at 1 HZ frequency. However, In case of Individual and Emission damaging misfire, MIL will be turned on when the malfunction is detected.
Especially, if injector connector/Ignition coil is disconnected for more than 46 sec., PCM sets DTC relating to misfire and conducts the fuel-cut to protect the catalyst.
Schematic Diagram (Part 1):
Schematic Diagram (Part 2):
Monitor DTC Status
1. Check DTC Status
1. Connect scantool to Data Link Connector(DLC).
2. IG "ON".
3. Select "Diagnostic Trouble Codes(DTCs)" mode, and then Press F5(INFO) to check DTC's information from the DTCs menu
4. Read "DTC Status" parameter.
5. Is parameter displayed "Present fault"?
YES
a. Go to "System Inspection" procedure.
NO
a. Although the misfire does not occur when the vehicle is brought to workshop, misfire can be reproduced when the condition is met. Drive the vehicle according to the freeze frame data in order to satisfy the condition.
System Inspection
1. Check Spark Plug
1. Remove cylinder's spark plugs
2. Visually/physically inspect the following items:
- Damaged insulation, Worn electrodes, Oil or fuel fouled, Loose terminals and cracks
- Check for plug gap : 1.0 - 1.1 mm (0.039 - 0.043 in.)
- Check if the spark plug for the relevant cylinder is lighter in color than the other plugs.
3. Has a problem been found in any of the above areas?
YES - Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO - Go to "Check Air Leakage" as indicated below
2. Check Air Leakage
1. Visually/physically inspect the air leakage in intake/exhaust system as following items,
- Vacuum hoses for splits, kinks and improper connections.
- Throttle body gasket
- Gasket between intake manifold and cylinder head
- Seals between intake manifold and fuel injectors
- Exhaust system between HO2S and Three way catalyst for air leakage
2. Has a problem been found in any of the above areas?
YES - Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO - Go to "Check for air leakage in Positive Crankcase Ventilation Valve(PCV)
3. Check for air leakage in Positive Crankcase Ventilation Valve(PCV)
1. Remove PCV valve from cylinder head cover by puling ventilation hose
2. With engine idling block PCV valve opening
3. Verify that vacuum is felt
4. Remove PCV valve
5. Blow through valve from port "A" and verify that air comes out of port "B"
6. Blow through valve from port "B" and verify that no air comes out of port "A"
7. Has a problem been found ?
YES - Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO - Go to "Check Compression pressure" as indicated below
4. Check Compression pressure
1. Warm up the engine to normal operating temperature
2. Disconnect the spark plug cables and remove the spark plugs.
3. Crank the engine to remove any foreign material in the cylinders.
4. Put compression pressure gauge into spark plug hole
5. Crank the engine with wide opened throttle valve and check compression pressure at each cylinder
Specification : 1323 kPa (13.5 kg/sq.cm,192 psi)
6. Is compression pressure for each cylinder displayed within specifications ?
YES - Go to "Check Timing" as indicated below
NO
- Add a small amount of oil through the spark plug hole, and repeat above steps. If the addition of oil causes the compression to rise, the cause is a worn or damaged piston ring or cylinder inner surface.
- If the compression remains the same, the cause is a burnt or defective valve seat, or pressure is leaking from the gasket. Repair as necessary and go to "Verification of Vehicle Repair" procedure
5. Check Timing
1. Ignition "OFF"
2. Monitor these signal waveforms from CAM and Crank shaft position Sensor are correctly aligned.
Reference : The 17th of CKP signal from missing tooth is aligned with high point of CMP signal
3. Are all timing marks aligned correctly ?
YES - Go to "Check Fuel Pressure" as indicated below
NO - Check that Cam, Crank and Oil pump sprocket timing marks are correctly aligned. Repair or readjust as necessary and go to "Verification of Vehicle Repair" procedure
6. Check fuel pressure
CAUTION
1. Be cautious that Fuel is explosive and an empty fuel tank can still contain explosive gases. When working on fuel system make sure to supply adequate ventilation to the work area. Do not smoke, and keep sparks and open flames away.
2. The fuel system remains under pressure when the engine is not running. Release fuel system pressure before disconnecting any fuel line to reduce the chance of personal injury or fire damage to vehicle components.
1. IG "OFF" and disconnect Fuel Pump Relay in Junction Box.
2. Start-up and wait until it stops itself.
3. IG "OFF" and connect Fuel Pump Relay.
4. Install the fuel pressure gauge to the delivery pipe with the fuel pressure gauge adaptor.
5. Activate the fuel pump, and with fuel pressure applied, check that there is no fuel leakage from the pressure gauge or connection part.
6. Measure the fuel pressure at idle.
Specifications : 374.6 - 384.4 kPa (3.82 - 3.92 kg/sq.cm, 54.3 - 55.8 psi)
7. Is the measured fuel pressure within specifications ?
YES
a. Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
NO
a. Repair or replace according to the below table. And then, go to "Verification of Vehicle Repair" procedure.
Verification of Vehicle Repair
After a repair, it is essential to verify that the fault has been corrected.
1. Connect scan tool and select "Diagnostic Trouble Codes(DTCs)" mode
2. Press F5(INFO) and confirm that "DTC Readiness Flag" indicates "Complete". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions
3. Read "DTC Status" parameter
4. Is parameter displayed "History(Not Present) fault"?
YES - System performing to specification at this time. Clear the DTC
NO - Go to the applicable troubleshooting procedure.