Part Three
Control System DTCs
DTC Troubleshooting: P0300, P0301, P0302, P0303, P0304
DTC P0300 : Random Misfire Detected
DTC P0301 : No. 1 Cylinder Misfire Detected
DTC P0302 : No. 2 Cylinder Misfire Detected
DTC P0303 : No. 3 Cylinder Misfire Detected
DTC P0304 : No. 4 Cylinder Misfire Detected
59. Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay on the problem cylinder?
-YES- The ignition coil and spark plug are OK. Go to step 61.
-NO- There is a failure in the ignition coil or the spark plug. Go to step 60.
60. Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay on the problem cylinder?
-YES- The spark plug has a failure. Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then perform the Repair Confirmation.
61. Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Do the misfire counts stay on the problem cylinder after the fuel injector is swapped?
-YES- The fuel injector is OK. Go to step 62.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then perform the Repair Confirmation.
62. Inspect VTEC System
-1. Perform the VTEC rocker arm test. Testing and Inspection
Does the engine pass the VTEC rocker arm test?
-YES- Go to step 63.
-NO- Repair the VTEC system, and then perform the Repair Confirmation.
63. CKP Pattern Clear/Pattern Learn
-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.
-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern.
-3. Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts.
-4. Drive the vehicle under the conditions when the misfire was duplicated.
-5. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay on the problem cylinder?
-YES- Update the ECM/PCM with the latest software ECM/PCM Update or substitute a known-good ECM/PCM Service and Repair, and then perform the Repair Confirmation.
-NO- Perform the Repair Confirmation.
64. Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
-YES- Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 65.
65. Check Fuel Pressure
-1. Relieve the fuel pressure. Service and Repair
-2. Attach the fuel pressure gauge set and the fuel pressure gauge. Testing and Inspection
-3. Locate and record the fuel pressure specification for your vehicle.
-4. Start the engine and record the fuel pressure under the conditions the misfire was duplicated.
Is the fuel pressure within specifications?
-YES- The fuel pressure is OK. Go to step 66.
-NO- Check for pinched or damaged fuel lines. If OK, replace the fuel tank unit Fuel Tank Unit Removal/Installation, and then perform the Repair Confirmation.
66. Check Fuel Contamination
-1. Remove the fuel tank unit. Fuel Tank Unit Removal/Installation
-2. Inspect for evidence of fuel contamination such as diesel fuel, water, rust, or debris.
NOTE: If the misfire occurred shortly after refueling, the likely cause is poor fuel quality. The MIL DIST (MIL distance) value in the DATA LIST, along with the fuel level, can help you make this determination.
Incorrect or contaminated fuel typically affects multiple cylinders. But a problem such as water in the fuel can cause a single cylinder misfire that occurs randomly.
Is there evidence of fuel contamination?
-YES- Replace the fuel filter and then drain/refill the fuel tank with a known-good fuel. Perform the Repair Confirmation.
-NO- The fuel system has no signs of fuel contamination. Go to step 67.
67. Exchange Fuel Injector
-1. Exchange the fuel injector from the problem cylinder with one from another cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Do the misfire counts stay on the problem cylinder after the fuel injector is swapped?
-YES- The fuel injector is OK. Go to step 68.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then perform the Repair Confirmation.
68. Inspect VTEC System
-1. Perform the VTEC rocker arm test. Testing and Inspection
Does the engine pass the VTEC rocker arm test?
-YES- Go to step 69.
-NO- Repair the VTEC system, and then perform the Repair Confirmation.
69. Check for Exhaust Restrictions
-1. Reinstall all removed parts, and reconnect all connectors.
-2. Record the MAP SENSOR value while the engine is off.
-3. Start the engine and monitor the ENGINE SPEED and MAP SENSOR in the DATA LIST with the HDS.
-4. Raise the engine speed to 3500 rpm and hold the throttle steady.
Does the MAP SENSOR read near atmospheric pressure (engine off value)?
-YES- There is a restriction in the exhaust system. Check for catalyst damage and repair as necessary. Perform the Repair Confirmation.
-NO- Go to step 70.
70. CKP Pattern Clear/Pattern Learn
-1. Select CRANK PATTERN in the ADJUSTMENT MENU with the HDS.
-2. Select CRANK PATTERN CLEAR, and clear the CKP pattern.
-3. Select CRANK PATTERN LEARNING with the HDS, and follow the screen prompts.
-4. Drive the vehicle under the conditions when the misfire was duplicated.
-5. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay on the problem cylinder?
-YES- Update the ECM/PCM with the latest software ECM/PCM Update or substitute a known-good ECM/PCM Service and Repair, and then perform the Repair Confirmation.
-NO- Perform the Repair Confirmation.
71. Check MAP Sensor Fluctuation
-1. Start the engine, and let it idle until the cooling fans cycle twice.
-2. Turn off all engine and electrical loads (AC, radio, lights, etc.).
-3. Configure a HIGH-SPEED SNAPSHOT, and select only the MAP SENSOR.
-4. Begin displaying live vehicle data on a line graph.
-5. Configure the MAP SENSOR line graph range for 1.2 V MAX and 0.8 V MIN.
-6. Watch the MAP SENSOR fluctuation. See examples below.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine cold?
-YES- The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 72.
-NO- The intake manifold vacuum fluctuation is OK. Go to step 75.
72. Adjust Valve Clearance
-1. Adjust the valve clearances Adjustments, and inspect the camshaft for excessive wear or grooves.
NOTE: ECT Sensor 1 must read less than 100 °F (38 °C) before adjusting the valve clearance. Short cutting this step may cause incorrect valve clearance and engine misfire.
-2. Recheck the MAP Sensor fluctuation at idle.
Does the MAP SENSOR continuously fluctuate 0.04 V or more at idle, no loads, engine cold?
-YES- Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 73.
-NO- The excessive MAP sensor fluctuation was caused by incorrect valve clearance. Perform the Repair Confirmation.
73. Check Cylinder Leakage
-1. Perform a cylinder leakage test. Engine Compression Test and Cylinder Leakage Test
-2. Record your test results in the chart shown below.
Does any cylinder have leakage greater than 10 %?
-YES- If the majority of the air is escaping from exhaust pipe or throttle body, check for tight valve clearance and adjust each cylinder as needed, then retest. Determine the cause of the cylinder leakage and repair the engine as needed, and then perform the Repair Confirmation.
-NO- The cylinders are sealing properly. Go to step 74.
74. Check Cylinder Compression
-1. Perform a cylinder compression test. Engine Compression Test and Cylinder Leakage Test
-2. Record your test results in a chart similar to the one shown below.
Does the compression vary more than 10 % between cylinders, or does any cylinder read below 150 PSI?
-YES- The cylinder leakage is normal, but the engine compression is low. Check for each of the conditions below and repair as needed, and then perform the Repair Confirmation.
* Incorrect camshaft timing.
* A bent (short) connecting rod.
* Worn or damaged camshaft lobes.
-NO- The engine compression and cylinder leakage is normal. Go to step 75.
75. Check Fuel Injector Leak Down
-1. Connect the fuel pressure gauge set. Testing and Inspection
-2. Ensure that the fuel shut off valve is on the fuel pump side of the pressure gauge.
-3. Start the engine and then shut it off.
-4. Turn the shut off valve 90° to isolate the pressure between the fuel injectors and the fuel pressure gauge.
-5. Record the initial fuel pressure reading.
-6. Let the vehicle sit for 10 minutes.
-7. Check the fuel pressure.
Does the pressure drop more than 10 PSI within 10 minutes?
-YES- The fuel injectors are leaking. Replace the fuel injectors Service and Repair, and then perform the Repair Confirmation.
-NO- The fuel injectors are not leaking. Go to step 76.
76. Inspect Spark Plug
-1. Remove the spark plug from the problem cylinder.
-2. Inspect the spark plug for signs of failure. Also make sure the spark plugs are the correct part number for the vehicle.
Does the spark plug show any signs of failure or is it not the correct part number?
-YES- Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- Go to step 77.
77. Exchange Spark Plug and Ignition Coil
-1. Exchange the spark plug and the ignition coil with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay on the problem cylinder?
-YES- The ignition coil and spark plug are OK. Go to step 79.
-NO- There is a failure in the ignition coil or the spark plug. Go to step 78.
78. Exchange Ignition Coil
-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay on the problem cylinder?
-YES- The spark plug has a failure. Replace the spark plug Service and Repair, and then perform the Repair Confirmation.
-NO- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then perform the Repair Confirmation.
79. Block-Off EGR Valve
-1. Loosen the EGR valve nuts enough to lift the valve about 3 mm. Do not remove the nuts.
-2. Slide a suitable block-off plate the size of a business card between the valve and the exhaust passages.
-3. Tighten the EGR valve nuts.
-4. Operate the vehicle under the conditions where the misfire was duplicated.
Did the misfire counts stop or significantly reduce?
-YES- A leaking EGR valve is causing the misfire. Replace the EGR valve Service and Repair, and then perform the Repair Confirmation.
-NO- The misfire is not caused by a leaking EGR valve. Go to step 80.
80. Engine Carbon Removal
-1. Perform a top engine cleaning following the product manufacturer's instructions.
-2. Drive the vehicle under the conditions when the misfire was duplicated.
-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Did the misfire counts stay?
-YES- The carbon removal procedure did not correct the misfire. Replace the fuel injectors Service and Repair, and then perform the Repair Confirmation.
-NO- The carbon removal procedure corrected the misfire. Perform the Repair Confirmation.
Repair Confirmation
-1. Reinstall all removed parts, and reconnect all connectors.
-2. Turn the ignition switch to ON (II).
-3. Reset the ECM/PCM with the HDS. How To Troubleshoot The Fuel And Emissions Systems
-4. Clear the CKP pattern with the HDS. How To Troubleshoot The Fuel And Emissions Systems
-5. Do the ECM/PCM idle learn procedure. ECM/PCM Idle Learn Procedure
-6. Do the CKP pattern learn procedure. How To Troubleshoot The Fuel And Emissions Systems
-7. Drive the vehicle under the conditions that you noticed the misfire while monitoring these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE
Do any of the cylinders display misfire counts?
-YES- The engine is still misfiring. Go to step 1 in the Failure Confirmation procedure and ensure that you selected the correct troubleshooting procedure.
-NO- The misfire problem has been fixed. Clear the DTC.