P0304

The content of this article reflects the changes identified in TSB - 10-13-007.

Injector Circuit:

Connectors: A-21X, B-01, B-02, B-05, B-06, B-25, B-26, B-48, C-51 <M/T>, C-52 <A/T>:

Misfire Detected circuit

CIRCUIT OPERATION
- The injector power is supplied from the MFI relay (terminal 1).
- The ECM or PCM controls the injector by turning the power transistor in the ECM or PCM ON" and "OFF."

TECHNICAL DESCRIPTION
- If a misfire occurs while the engine is running, the engine speed changes for an instant.
- The ECM or PCM checks for such changes in engine speed.

DTC SET CONDITIONS

Check Conditions
- Five seconds or more have passed after the engine was started.
- Engine speed is between 440 and 6,000 r/min.
- Engine coolant temperature is higher than -10°C (14°F).
- Intake air temperature is higher than -10°C (14°F).
- Barometric pressure is higher than 76 kPa (11 psi).
- Adaptive learning is complete for the vane which generates a crankshaft position signal.
- While the engine is running, excluding gear shifting, deceleration, sudden acceleration/deceleration and A/C compressor switching.

Judgement Criteria (change in the angular acceleration of the crankshaft is used for misfire detection).
- Misfire has occurred in 4 or more of the last 200 revolutions [when the catalyst temperature is higher than 950°C (1,742°F)].

or

- Misfire has occurred in 20 or more of the last 1,000 revolutions (corresponding to 1.5 times the limit of emission standard).

TROUBLESHOOTING HINTS
The most likely causes for this code to be set are:
- Fuel aeration due to low fuel level.
- Ignition system related part(s) failed.
- Low compression pressure.
- Injector failed.
- ECM failed.
- PCM failed.

DIAGNOSIS

Check whether fuel may be aerated due to low fuel level.
^ Check whether users have experienced the lack of fuel or not.

Q: Has the user ever experienced the lack of fuel?

YES: Ensure fuel level is not low, erase the DTC, and re-evaluate for misfire condition using the appropiate OBD-II Drive Cycle Procedure.

NO: Go to Step 1.

CAUTION:
- Do not attempt to adjust the gap of the platinum plug.
- Cleaning of the platinum plug may result in damage to the platinum tips. Therefore, if carbon deposits must be removed, use a plug cleaner and complete cleaning within 20 seconds to protect the electrode.
Do not use a wire brush.

STEP 1 Check the spark plugs.
1. Check the plug gap and replace if the limit is exceeded.
2. For the right bank cylinder, remove the intake manifold.

Standard value: 1.0 - 1.1 mm (0.039 - 0.043 inch)
Limit: 1.3 mm (0.051 inch)

If within specifications, go to Step 2.

If not within specifications, replace the faulty spark plug.
Then go to Step 13.

STEP 2. Check the spark plugs cable.

NOTE: Flex the cable while testing to look for intermittent
problems.

1. Check the cap and coating for cracks.
2. Measure the resistance.
Limit: maximum 22 kohms

If within specifications, go to Step 3.

If not within specifications, replace the faulty spark plug cable. Then go to Step 13.

STEP 3. Check the left bank injector.
1. Disconnect the left bank injector connector.

2. Measure the resistance between each injector side connector terminals 1 and 2.

Standard value: 13 - 16 ohms [at 20°C (68°F)]

If within specifications, go to Step 4. If not within specifications, replace the injector. Then go to Step 13.

STEP 4. Check injector intermediate connector B-48 at the right bank injector.
1. Disconnect the injector intermediate harness connector.

2. Measure the resistance between injector side connector terminals 1 and 2 (No.1 injector), 1 and 3 (No.3 injector), 1 and 4 (No.5 injector).

Standard value: 13 - 16 ohms [at 20°C (68°F)]

If within specifications, go to Step 7.

If not within specifications, go to Step 5.

STEP 5. Check the right bank injector.
1. Disconnect the injector connector deviated from the standard value in Step 4.

2. Measure the resistance between injector side connector terminals 1 and 2.

Standard value: 13 - 16 ohms [at 20°C (68°F)]

If within specifications, go to Step 10.

If not within specifications, replace the injector. Then go to Step 13.

STEP 6. Check harness connector B-01 or B-05 or B-26 at the right bank injector for damage.
1. Check the injector connector deviated from the standard value in Step 4.

If harness connector is in good condition, repair the harness wire between the injector connector and injector intermediate harness connector. Then go to Step 13.

If harness connector is damaged, repair or replace it.
Refer to Harness Connector Inspection. Then go to Step 13.

STEP 7. Check harness connector B-48 at injector intermediate connector B48 for damage.
If harness connector B-48 is in good condition, go to Step 8.

If harness connectors B-48 is damaged, repair or replace it. Refer to Harness Connector Inspection Then go to Step 13.

STEP 8. Check harness connector B-02, B-06, B-25 at the left bank injector for damage.
If harness connectors B-02, B-06, B-25 are in good condition, go to Step 9.

If harness connectors B-02, B-06, B-25 are damaged repair or replace them.
Refer to Harness Connector Inspection. Then go to Step 13.

STEP 9. Check harness connector C-51 at the ECM or harness connector C-52 at the PCM for damage.
If harness connector C-51 or C-52 is in good condition, go to Step 10.

If harness connector C-51 or C-52 is damaged, repair or replace it.
Refer to Harness Connector Inspection. Then go to Step 13.

STEP 10. Check the harness wire between injector connectors B-01, B-02, B-05, B-06, B-25, B-26 and the ECM connector C-51 or PCM connector C-52 .

If the wire between the injector connectors B-01, B-02, B-05, B-06, B-25, B-26 and the ECM connector C-51 or PCM connector C-52 are not damaged, go to Step 11.

If the wire between the injector connectors B-01, B-02, B-05, B-06, B-25, B-26 and the ECM connector C-51 or PCM connector C-52 is damaged, repair it. Then go to Step 13.

STEP 11. Check the compression.
Refer to On-vehicle Service - Compression Pressure Check.
If correct, go to Step 12.

If incorrect, repair it. Then go to Step 13.

STEP 12. Replace all the injectors.
1. Replace all the injectors.
2. Carry out a test drive with the drive cycle pattern. Refer to Procedure 6 - Other Monitor.
3. Check for the diagnostic trouble code (DTC).

If DTC P0301, P0302, P0303, P0304, P0305, P0306 are not output, the inspection is complete.

If DTC P0301 P0302, P0303, P0304, P0305, P0306 are output, replace the ECM or PCM. Then go to Step 13.

STEP 13. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Procedure 6 - Other monitor.
2. Read the diagnostic trouble code, and confirm that diagnostic trouble code P0301, P0302, P0303, P0304, P0305, P0306 does not reset.