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

NOTE:
* Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information How to Troubleshoot the Fuel And Emissions Systems.
* Do not clear the DTC until the cause of the misfire is fixed. Valuable data required for troubleshooting will be lost if the DTC is cleared. The data will also be lost even if freeze data and the on-board snapshot is saved.
* If the misfire is frequent enough to trigger detection of increased emissions during two consecutive driving cycles, the MIL will come on, and DTC P0300 (and some combination of P0301 through P0304) will be stored.
* If the misfire is frequent enough to damage the catalyst, the MIL will flash whenever the misfire occurs, and DTC P0300 (and some combination of P0301 through P0304) will be stored. When the misfire stops, the MIL will remain on.
* Troubleshoot the following DTCs first, if any of them were stored along with the random misfire DTC(s) (Because parts can sometimes fail without setting DTC's you should also do a physical inspection of the systems listed below):

P0102, P0103: MAF sensor

P0107, P0108: MAP sensor

P0171, P0172: Fuel system

P0201, P0202, P0203, P0204: No. 1-No. 4 cylinder injector

P0335, P0339: CKP sensor

P0365, P0369: CMP sensor B

P0351, P0352, P0353, P0354: No. 1 -No. 4 cylinder ignition coil(s)

P2646, P2647, P2648, P2649: VTEC system


61. 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 at the problem cylinder?
-YES- The spark plug has a failure. Replace the spark plug Service and Repair, and then do the Repair verification.
-NO- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then do the Repair verification.

62. 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 at the problem cylinder when the fuel injector is swapped?
-YES- The fuel injector is OK. Go to step 63.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then do the Repair verification.

63. 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 64.
-NO- Repair the VTEC system, and then do the Repair verification.

64. 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 at the problem cylinder?
-YES- Update the PCM with the latest software PCM Update or substitute a known-good PCM Service and Repair, and then do the Repair verification.
-NO- Perform the Repair Confirmation.

65. 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 do the Repair verification.
-NO- Go to step 66.

66. 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 67.
-NO- Check for pinched or damaged fuel lines. If OK, replace the fuel tank unit Fuel Tank Unit Removal/Installation, and then do the Repair verification.

67. 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 Fuel Tank Unit Disassembly And Reassembly 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 68.

68. 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 at the problem cylinder when the fuel injector is swapped?
-YES- The fuel injector is OK. Go to step 69.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then do the Repair verification.

69. 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 70.
-NO- Repair the VTEC system, and then do the Repair verification.

70. 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 71.

71. 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 at the problem cylinder?
-YES- Update the PCM with the latest software PCM Update or substitute a known-good PCM Service and Repair, and then do the Repair verification.
-NO- Perform the Repair Confirmation.

72. 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 73.
-NO- The intake manifold vacuum fluctuation is OK. Go to step 76.

73. 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. Shortcutting 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 74.
-NO- The excessive MAP sensor fluctuation was caused by incorrect valve clearance. Perform the Repair Confirmation.

74. Check Cylinder Leakage

-1. Perform a cylinder leakage test. Testing and Inspection

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 do the Repair verification.
-NO- The cylinders are sealing properly. Go to step 75.

75. Check Cylinder Compression

-1. Perform a cylinder compression test. Testing and Inspection

-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 do the Repair verification.
* 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 76.

76. 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 do the Repair verification.
-NO- The fuel injectors are not leaking. Go to step 77.

77. 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 do the Repair verification.
-NO- Go to step 78.

78. Exchange Spark Plug and Ignition Coil

-1. Exchange the spark plug and the ignition coil with 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 at the problem cylinder?
-YES- The ignition coil and spark plug are OK.
* If you have already performed a cylinder leakage and compression test, go to step 82.
* If you have not performed a cylinder leakage and compression test, go to step 80.
-NO- There is a failure in the ignition coil or the spark plug. Go to step 79.

79. 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 at the problem cylinder?
-YES- The spark plug has a failure. Replace the spark plug Service and Repair, and then do the Repair verification.
-NO- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then do the Repair verification.

80. Check Cylinder Leakage

-1. Perform a cylinder leakage test. Testing and Inspection

-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 do the Repair verification.
-NO- The cylinders are sealing properly. Go to step 81.

81. Check Cylinder Compression

-1. Perform a cylinder compression test. Testing and Inspection

-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 do the Repair verification.
* 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 82.

82. 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 do the Repair verification.
-NO- The carbon removal procedure corrected the misfire. Perform the Repair Confirmation.

Repair verification

-1. Reinstall all removed parts, and reconnect all connectors.

-2. Turn the ignition switch to ON (II).

-3. Reset the 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 PCM idle learn procedure. 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 Problem verification procedure and ensure that you selected the correct troubleshooting procedure.
-NO- The misfire problem has been fixed. Clear the DTC.