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

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 this freeze data: Engine speed Vehicle speed Throttle position CLV Clear the DTC with the HDS. Start the engine without load (in Park or neutral), then let it idle. Monitor the OBD STATUS for DTC P0301, P0302, P0303 or P0304 in the DTCs MENU with the HDS. Does the screen indicate FAILED?
YES | - | Go to Step 9 .
NO | - | If the screen indicates PASSED, go to Step 5 . If the screen indicates EXECUTING, keep the driving condition continually until a result comes on. If the screen indicates OUT OF CONDITION, wait for several minutes and recheck.
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 Step 9 .
NO | - | Go to Step 6 .
Test-drive the vehicle for several minutes in the range of the recorded freeze data. Monitor the OBD STATUS for DTC P0301, P0302, P0303 or P0304 in the DTCs MENU with the HDS. Does the screen inidcated FAILED?
YES | - | Go to Step 9 .
NO | - | If the screen indicates PASSED, go to Step 8 . If the screen indicates EXECUTING, keep the driving condition continually until a result comes on. If the screen indicates OUT OF CONDITION, go to Step 6 and recheck.
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 Step 9 .
NO | - | Intermittent failure, system is OK at this time.■
Turn the ignition switch OFF. Remove the intake manifold cover. Start the engine, and listen for a clicking sound at the injector of the problem cylinder. Does the injector click?
YES | - | Go to Step 12 .
NO | - | Go to Step 57 .
Turn the ignition switch OFF. Exchange the ignition coil from the problem cylinder with one from another cylinder. Test-drive the vehicle for several minutes in the range of the recorded freeze data. 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 Step 16 .
NO | - | Intermittent misfire due to poor contact at the ignition coil connector (no misfire at this time). Make sure the coil connections are secure.■
Determine which cylinder had the misfire. Does the misfire occur in the cylinder where the ignition coil was moved?
YES | - | Replace the faulty ignition coil, then go to Step 62 .
NO | - | Go to Step 17 .
Turn the ignition switch OFF. Exchange the spark plug from the problem cylinder with one from another cylinder. Test-drive the vehicle for several minutes in the range of the recorded freeze data. 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 Step 21 .
NO | - | Intermittent misfire due to spark plug fouling (no misfire at this time).■
Determine which cylinder had the misfire. Does the misfire occur in the cylinder where the spark plug was moved?
YES | - | Replace the faulty spark plug, then go to Step 62 .
NO | - | Go to Step 22 .
Turn the ignition switch OFF. Exchange the injector from the problem cylinder with one from the another cylinder. Start the engine, and let it idle 2 minutes. Test-drive the vehicle for several minutes in the range of the recorded freeze data. 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 Step 27 .
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.■
Determine which cylinder had the misfire. Does the misfire occur in the cylinder where the injector was moved?
YES | - | Replace the faulty injector, then go to Step 62 .
NO | - | Go to Step 28 .
Turn the ignition switch OFF. Disconnect the ignition coil 3P connector from the problem cylinder. Turn the ignition switch ON (II). Measure voltage between ignition coil 3P connector terminal No. 3 and body ground. Is there battery voltage?
YES | - | Go to Step 32 .
NO | - | Repair open in the wire between the ignition coil and the ignition coil relay, then go to Step 62 .
Turn the ignition switch OFF. |

Check for continuity between ignition coil 3P connector terminal No. 2 and body ground. Is there continuity?
YES | - | Go to Step 34 .
NO | - | Repair open in the wire between the ignition coil and G101, then go to Step 62 .
Turn the ignition switch OFF. Jump the SCS line with the HDS. Disconnect ECM/PCM connector A (31P). |

Check for continuity between body ground and the appropriate ECM/PCM connector terminal (see table).
PROBLEM CYLINDER | DTC | ECM/PCM TERMINAL | WIRE COLOR
--- | --- | --- | ---
No. 1 | P0301 | A16 | YEL/GRN
No. 2 | P0302 | A15 | BLU/RED
No. 3 | P0303 | A14 | WHT/BLU
No. 4 | P0304 | A13 | BRN
Is there continuity?
YES | - | Repair short in the wire between the ECM/PCM and the ignition coil, then go to Step 62 .
NO | - | Go to Step 38 .

Connect appropriate ignition coil 3P connector terminal No. 1 to body ground with a jumper wire (see table).
PROBLEM CYLINDER | DTC | WIRE COLOR
--- | --- | ---
No. 1 | P0301 | YEL/GRN
No. 2 | P0302 | BLU/RED
No. 3 | P0303 | WHT/BLU
No. 4 | P0304 | BRN

Check for continuity between body ground and the appropriate ECM/PCM connector terminal (see table).
PROBLEM CYLINDER | DTC | ECM/PCM TERMINAL | WIRE COLOR
--- | --- | --- | ---
No. 1 | P0301 | A16 | YEL/GRN
No. 2 | P0302 | A15 | BLU/RED
No. 3 | P0303 | A14 | WHT/BLU
No. 4 | P0304 | A13 | BRN
Is there continuity?
YES | - | Go to Step 40 .
NO | - | Repair open in the wire between the ECM/PCM and the ignition coil, then go to Step 62 .
Reconnect the ignition coil 3P connector and ECM/PCM connector A (31P). Do an engine compression and a cylinder leakdown test. Did the engine pass both tests?
YES | - | Go to Step 42 .
NO | - | Repair the engine, then go to Step 63 .
Do the VTEC rocker arm test. Did the engine pass test?
YES | - | Go to Step 70 .
NO | - | Repair as necessary, then go to Step 63 .
Turn the ignition switch OFF. Jump the SCS line with the HDS. Disconnect ECM/PCM connector B (24P). Turn the ignition switch ON (II). |

Measure voltage between body ground and the appropriate ECM/PCM connector terminal (see table).
PROBLEM CYLINDER | DTC | ECM/PCM TERMINAL | WIRE COLOR
--- | --- | --- | ---
No. 1 | P0301 | B5 | BRN
No. 2 | P0302 | B4 | RED
No. 3 | P0303 | B3 | BLU
No. 4 | P0304 | B2 | YEL
Is there battery voltage?
YES | - | Go to Step 56 .
NO | - | Go to Step 48 .
Turn the ignition switch OFF. Disconnect the injector 2P connector from the problem cylinder. Turn the ignition switch ON (II). |

Measure voltage between injector 2P connector terminal No. 1 and body ground. It there battery voltage?
YES | - | Go to Step 52 .
NO | - | Repair open in the wire between the injector and PGM-FI main relay 1 (FI MAIN), then go to Step 62 .
Turn the ignition switch OFF. |

Check for continuity between body ground and the appropriate ECM/PCM connector terminal (see table).
PROBLEM CYLINDER | DTC | ECM/PCM TERMINAL | WIRE COLOR
--- | --- | --- | ---
No. 1 | P0301 | B5 | BRN
No. 2 | P0302 | B4 | RED
No. 3 | P0303 | B3 | BLU
No. 4 | P0304 | B2 | YEL
Is there continuity?
YES | - | Repair short in the wire between the ECM/PCM and the injector, then go to Step 62 .
NO | - | Go to Step 54 .

Connect appropriate injector 2P connector terminal No. 2 to body ground with a jumper wire (see table).
PROBLEM CYLINDER | DTC | WIRE COLOR
--- | --- | ---
No. 1 | P0301 | BRN
No. 2 | P0302 | RED
No. 3 | P0303 | BLU
No. 4 | P0304 | YEL

Check for continuity between body ground and the appropriate ECM/PCM connector terminal (see table).
PROBLEM CYLINDER | DTC | ECM/PCM TERMINAL | WIRE COLOR
--- | --- | --- | ---
No. 1 | P0301 | B5 | BRN
No. 2 | P0302 | B4 | RED
No. 3 | P0303 | B3 | BLU
No. 4 | P0304 | B2 | YEL
Is there continuity?
YES | - | Go to Step 56 .
NO | - | Repair open in the wire between the ECM/ PCM and the injector, then go to Step 62 .

Measure resistance between injector 2P connector terminals No. 1 and No. 2. Is there 10−13 Ω?
YES | - | Go to Step 57 .
NO | - | Replace the injector, then go to Step 62 .
Substitute a known-good injector from another cylinder to the problem cylinder. Reconnect ECM/PCM connector B (24P). Start the engine, and let it idle 2 minutes. Test-drive the vehicle for several minutes in the range of the recorded freeze data. 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 Step 71 .
NO | - | Replace the original injector, then go to Step 62 .
Reconnect all connectors. Turn the ignition switch ON (II). Reset the ECM/PCM with the HDS. Clear the CKP pattern with the HDS. Do the ECM/PCM idle learn procedure. Do the CKP pattern learn procedure. Test-drive the vehicle for several minutes in the range of the recorded freeze data. 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 are indicated, check for poor connections or loose terminals at the ignition coil, the injector, and the ECM/PCM, then troubleshoot DTC P0300, P0301, P0302, P0303 or P0304. If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.
NO | - | Go to Step 70 .
Monitor the OBD STATUS for DTC P0301, P0302, P0303 or P0304 in the DTCs MENU with the HDS. Does the screen indicate PASSED?
YES | - | Troubleshooting is complete.■
NO | - | If the screen indicates FAILED, then go to Step 1 and recheck. If the screen indicates EXECUTING, keep the driving condition continually until a result comes on. If the screen indicates OUT OF CONDITION, go to Step 68 and recheck.
Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM. Test-drive the vehicle for several minutes in the range of the recorded freeze data. 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 are indicated, check for poor connections or loose terminals at the injector, the ignition coil, and the ECM/PCM, then go to Step 1 . If any other Temporary DTCs or DTCs are indicated, go to the indicated DTC's troubleshooting.
NO | - | If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM. ■