## DTC Troubleshooting: P0301 (71), P0302 (72), P0303 (73), P0304 (74)

DTC P0301: | No. 1 Cylinder Misfire
DTC P0303: | No. 3 Cylinder Misfire

NOTE:
Troubleshoot the following DTCs first if any of them were stored along with the random misfire DTC(s):
P0068, P0106, P0107, P0108: Manifold absolute pressure (MAP) sensor
P0171, P0172: Fuel system
P0201-P0204, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271: Injector
P0335, P0339: Crankshaft position (CKP) sensor
P0342, P0343, P0344: Camshaft position (CMP) sensor
P0351-P0358: Ignition coil
P0506, P0507: Idle control system
P0401, P0403, P0404, P0405, P0406, P0409, P0489, P0490: Exhaust gas recirculation (EGR) system

1. | Record the following freeze data. Engine speed Vehicle speed Throttle position CLV

2. | Do the DTC CLEAR in the CLEAR MENU with the HDS.

3. | Start the engine with no load (in neutral), then let it idle.

4. | Monitor the OBD STATUS for DTC P0301, P0302, P0303 or P0304 in the DTCs MENU with the HDS. Is it FAILED? YES - Go to 9. NO - If it is PASSED, go to 5. If it is EXECUTING, keep the driving condition continually until a result comes on. If it is Out of CONDITION, wait for several minutes, and recheck.

5. | Check the CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE in the DATA LIST for 10 minutes with the HDS. Does CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE show misfire counts? YES - Go to 9. NO - Go to 6.

6. | Test-drive the vehicle for several minutes in the range of the recorded freeze data.

7. | Monitor the OBD STATUS for DTC P0301, P0302, P0303 or P0304 in the DTCs MENU with the HDS. Is it FAILED? YES - Go to 9. NO - If it is PASSED, go to 8. If it is EXECUTING, keep the driving condition continually until a result comes on. If it is Out of CONDITION, go to 6 and recheck.

8. | Check the CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE in the DATA LIST for 10 minutes with the HDS. Does CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE show misfire counts? YES - Go to 9. NO - Intermittent failure, system is OK at this time.n

9. | Turn the ignition switch OFF.

10. | Exchange the ignition coil from the problem cylinder with one from another cylinder. The front ignition coil and the rear ignition coil are exchanged simultaneously. The front ignition coil cannot be interchanged with the rear ignition coil, as they are different in shape.

11. | Test-drive the vehicle for several minutes in the range of the recorded freeze data.

12. | Check the CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE in the DATA LIST for 10 minutes with the HDS. Does CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE show misfire counts? YES - Go to 13. NO - Intermittent misfire due to poor contact at the ignition coil connector (no misfire at this time). Make sure the coil connections are secure.n

13. | Determine which cylinder had the misfire. Does the misfire occur in the cylinder where the ignition coil was exchanged? YES - Replace the faulty ignition coil, then go to 26. NO - Go to 14.

14. | Turn the ignition switch OFF.

15. | Exchange the spark plug from the problem cylinder with one from another cylinder. NOTE: The front side spark plug and the rear side spark plug are exchanged simultaneously.

16. | Test-drive the vehicle for several minutes in the range of the recorded freeze data.

17. | Check the CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE in the DATA LIST for 10 minutes with the HDS. Does CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE show misfire counts? YES - Go to 18. NO - Intermittent misfire due to spark plug fouling (no misfire at this time).n

18. | Determine which cylinder had the misfire. Does the misfire occur in the cylinder where the spark plug was exchanged? YES - Replace the faulty spark plug, then go to 26. NO - Go to 19.

19. | Turn the ignition switch OFF.

20. | Exchange the injector from the problem cylinder with one from the another cylinder.

21. | Start the engine, and let it idle for 2 minutes.

22. | Test-drive the vehicle for several minutes in the range of the recorded freeze data.

23. | Check the CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE in the DATA LIST for 10 minutes with the HDS. Does CYL1 MISFIRE, CYL2 MISFIRE, CYL3 MISFIRE and/or CYL4 MISFIRE show misfire counts? YES - Go to 24. NO - Intermittent misfire due to bad contact in the injector connector (no misfire at this time). Check for poor connections or loose terminals at the injector.n

24. | Determine which cylinder had the misfire. Does the misfire occur in the cylinder where the injector was exchanged? YES - Replace the faulty injector, then go to 26. NO - Go to 25.

25. | Do an engine compression and a cylinder leakdown test. Did the engine pass both tests? YES - Go to 33. NO - Repair the engine, then go to 26.

26. | Reconnect all connectors.

27. | Turn the ignition switch ON (II).

28. | Do the ECM RESET in the CLEAR MENU with the HDS.

29. | Do the ETCS learn procedure.

30. | Test-drive the vehicle for several minutes in the range of the recorded freeze data.

31. | Check for Temporary DTCs or DTCs in the DTCs MENU with the HDS. Are any Temporary DTCs or DTCs indicated? YES - If DTC P0301, P0302, P0303 or P0304 is indicated, check for poor connections or loose terminals at the ignition coil, the injector, and the ECM, then go to troubleshooting DTC P0300, P0301, P0302, P0303 or P0304. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC troubleshooting. NO - Go to 32.

32. | Monitor the OBD STATUS for DTC P0301, P0302, P0303 or P0304 in the DTCs MENU with the HDS. Is it PASSED? YES - Troubleshooting is complete.n NO - If it is FAILED, then go to 1 and recheck. If it is EXECUTING, keep the driving condition continually until a result comes on. If it is Out of CONDITION, go to 30 and recheck.

33. | Substitute a known-good ECM.

34. | Test-drive the vehicle for several minutes in the range of the recorded freeze data.

35. | Check for Temporary DTCs or DTCs in the DTCs MENU with the HDS. Are any Temporary DTCs or DTCs indicated? YES - If DTC P0301, P0302, P0303 or P0304 is indicated, check for poor connections or loose terminals at the injector, the ignition coil, and the ECM, then go to 1. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC troubleshooting. NO - Replace the original ECM.n