Part One

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

1. Problem verification-Idle

-1. Record the FREEZE DATA and the ONBOARD SNAPSHOT with the HDS.

-2. Start the engine, and let it idle.

-3. Monitor these parameters in the DATA LIST:
* CYL1 MISFIRE
* CYL2 MISFIRE
* CYL3 MISFIRE
* CYL4 MISFIRE

Are the misfire counts increasing on any cylinder at idle?
-YES- The engine is misfiring at idle, go to step 2.
-NO- The engine does not misfire at idle, go to step 3.

2. Determine Affected Cylinders

-1. Continue to monitor the misfire parameters in the DATA LIST.

Are misfire counts generally isolated to a single cylinder?
-YES- The misfire is isolated to a single cylinder.
* If the misfire counts are increasing every engine revolution (completely inactive cylinder), start the Single Cylinder Continuous Misfire at Idle troubleshooting on step 6.
* If the misfire counts are increasing every few engine revolutions (partially inactive cylinder), start the Single Cylinder Non-Continuous Misfire at Idle troubleshooting on step 21.
-NO- The misfire affects multiple cylinders.
* If the misfire counts are increasing every engine revolution (completely inactive cylinder), start the Multiple Cylinder Continuous Misfire at Idle troubleshooting on step 30.
* If the misfire counts are increasing every few engine revolutions (partially inactive cylinder), start the Multiple Cylinder Non-Continuous Misfire at Idle troubleshooting on step 48.

3. Problem verification-Static Load

-1. Increase the engine speed to 3,500 RPM.

-2. Hold the engine speed steady, and monitor the misfire parameters in the DATA LIST.

Are the misfire counts increasing on any cylinder?
-YES- The engine is misfiring under load. Go to step 4.
-NO- The engine does not misfire under a static load. Go to step 5.

4. Determine Affected Cylinders

-1. Continue to monitor the misfire parameters in the DATA LIST.

Are misfire counts generally isolated to a single cylinder?
-YES- The misfire is isolated to a single cylinder, start the Single Cylinder Misfire. Under Load troubleshooting on step 58.
-NO- The misfire affects multiple cylinders, start the Multiple Cylinder Misfire. Under Load troubleshooting on step 65.

5. Problem verification - OBD Snapshot

-1. Open the ONBOARD SNAPSHOT with the HDS.

-2. Scroll through the snapshot, and find when the MISFIRE value begins to increase.

-3. Record the value of these parameters as the MISFIRE value increases:

-4. Drive the vehicle according to the conditions you identified above while monitoring the misfire counts.

Are the misfire counts increasing on any cylinder?
-YES- The engine is misfiring under the specific operating conditions above.
* If the misfire occurred when the engine was cold, start the Misfire When Cold troubleshooting on step 72.
* If the misfire occurred when the engine was loaded, go to step 4.
-NO- Intermittent failure; the engine is not misfiring at this time.
NOTE: If the misfire can not be reproduced, there is a possibility that the problem may have been caused by poor quality fuel. The problem may have disappeared after refueling with fresh fuel. The MIL DIST (MIL Distance) value in the Data List in combination with the fuel level may help you make this determination.

6. Check Ignition Coil Spark

-1. Turn the ignition switch to LOCK (0).

-2. Remove the ignition coil from the problem cylinder.

-3. Connect a commercially available spark tester between the ignition coil and engine ground.

-4. Start the engine with the ignition coil connected.

Does the ignition coil produce a spark?
-YES- The ignition coil wiring is OK. Go to step 14.
-NO- There is a problem with the ignition coil, or the Ignition coil circuit. Go to step 7.

7. Ignition Coil Check

-1. Exchange the ignition coil on the problem cylinder with a normally operating cylinder.

-2. Connect a commercially available spark tester between the ignition coil and engine ground.

-3. Start the engine with the ignition coil connected.

Does the ignition coil produce a spark?
-YES- The ignition coil has a failure. Replace the ignition coil Service and Repair, and then do the Repair verification.
-NO- There is a problem with the ignition coil circuit. Go to step 8.

8. Check Ignition Coil Power and Ground

-1. Disconnect the ignition coil 3P connector from the problem cylinder.

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

-3. Measure the voltage between ignition coil 3P connector terminals No. 1 (power) and No. 2 (ground).
NOTE: After the ignition switch is turned to LOCK (0), this circuit may still show battery voltage for a period of time. This is normal.

Is there battery voltage?
-YES- The ignition coil power and ground circuits are OK. Go to step 9.
-NO- There is a problem with the ignition coil power or ground circuit. Go to step 13.

9. Check Ignition Coil Control Short to Power

-1. Turn the ignition switch to ON (II).

-2. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.

Is there about 4 V or more?
-YES- The ignition coil control circuit is shorted to power. Go to step 10.
-NO- The ignition coil control circuit is not shorted to power. Go to step 11.

10. Isolate Ignition Coil Control Short to Power

-1. Jump the SCS line with the HDS.

-2. Turn the ignition switch to LOCK (0).

-3. Disconnect the PCM connectors.

-4. Turn the ignition switch to ON (II).

-5. Measure the voltage between ignition coil 3P connector terminals No. 3 (Ignition Control) and body ground.

Is there about 4 V or more?
-YES- There is a short to power on the ignition coil control circuit. Find and repair the failure, and then do the Repair verification.
-NO- The PCM is malfunctioning. Replace the PCM Service and Repair, and then do the Repair verification.

11. Check Ignition Coil Control Open Circuit

-1. Jump the SCS line with the HDS.

-2. Turn the ignition switch to LOCK (0).

-3. Disconnect the PCM connectors.

-4. Check for continuity between the ignition coil control terminal at the PCM connector and at the ignition coil 3P connector terminal No. 3.

Is there continuity?
-YES- The ignition coil control circuit is not open. Go to step 12.
-NO- Repair the open circuit between the ignition coil and the PCM, and then do the Repair verification.

12. Check Ignition Coil Control Short to Ground

-1. Check for continuity between the ignition coil control terminal at the ignition coil 3P connector terminal No. 3 and body ground.

Is there continuity?
-YES- Repair the short to ground on the ignition coil control wire, and then do the Repair verification.
-NO- The ignition coil control wiring is OK. Substitute a known good PCM Service and Repair, and then do the Repair verification.

13. Check Ignition Coil Power Circuit

-1. Measure the voltage between ignition coil 3P connector terminal No. 1 (power) and a known-good engine ground.

Is there battery voltage between the ignition coil power terminal and engine ground?
-YES- The power circuit is OK. Repair the open circuit between the ignition coil (3P connector terminal No. 2) and G102, and then do the Repair verification.
-NO- Repair the open circuit between the ignition coil and the ignition coil relay, and then do the Repair verification.

14. Inspect Ignition Coil

-1. Inspect the ignition coil and spark plug tube for engine oil contamination.

Is the ignition coil covered in engine oil?
-YES- Clean the oil from the ignition coil and spark plug tube. Replace the spark plug tube seals in the cylinder head cover Service and Repair, and then do the Repair verification.
-NO- Go to step 15.

15. Exchange Spark Plug and Ignition Coil

-1. Exchange the spark plug and the ignition coil with one from 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 ignition coil and spark plug are OK. Go to step 17.
-NO- There is a failure in the ignition coil or the spark plug. Go to step 16.

16. 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

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 18.

18. 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 19.

19. 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 20.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then do the Repair verification.

20. 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.

21. 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 22.

22. Inspect Ignition Coil

-1. Inspect the ignition coil and spark plug tube for engine oil contamination.

Is the ignition coil covered in engine oil?
-YES- Clean the oil from the ignition coil and spark plug tube. Replace the spark plug tube seals in the cylinder head Service and Repair cover, and then do the Repair verification.
-NO- Go to step 23.

23. 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. Go to step 25.
-NO- There is a failure in the ignition coil or the spark plug. Go to step 24.

24. 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.

25. 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 hot?
-YES- The intake manifold pressure fluctuation indicates a mechanical engine failure. Go to step 26.
-NO- The intake manifold vacuum fluctuation is OK. Go to step 29.

26. 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 hot?
-YES- Adjusting the valve clearance did not correct the excessive MAP sensor fluctuation. Go to step 27.
-NO- The excessive MAP sensor fluctuation was caused by incorrect valve clearance. Perform the Repair Confirmation.

27. 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 28.

28. 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 29.

29. 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. All of the failures have been checked for this type of misfire. Go to step 1 in the Problem verification procedure and ensure you selected the correct troubleshooting procedure.
-NO- The fuel injector is faulty. Replace the faulty fuel injector Service and Repair, and then do the Repair verification.

30. 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 31.