P0300

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

Injector Circuit:

Connector: A-21X, B-01, B-02, B-05, B-06, C-49 <M/T>, C-50 <A/T>:

Random Misfire 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 500 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 (equal 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.
- Poor crankshaft position sensor.
- Incorrect air/fuel ratio.
- Low compression pressure.
- Skipping of timing belt teeth.
- EGR system and EGR valve failed.
- ECM failed.
- PCM failed.

DIAGNOSIS
Required Special Tool:
MB991502: Scan Tool (MUT-II)

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

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.

STEP 1. Using scan tool MB991502, check data list item 22: Crankshaft Position Sensor.
1. Connect scan tool MB991502 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991502 to the data reading mode for item 22, Crankshaft Position Sensor.
4. Check the waveform of the crankshaft position sensor while keeping the engine speed constant.
- The pulse width should be constant.

If constant, go to Step 2.
If not constant, refer to DTC P0335 - Crankshaft Position Sensor Circuit Malfunction.

STEP 2. Using scan tool MB991502, check data list item 81: Long-Term Fuel Trim.
1. Start the engine and run at idle.
2. Set scan tool MB991502 to the data reading mode for item 81, Long-Term Fuel Trim.
- The fuel trim should be between -12.5 and +12.5 when the load is 2,500 r/min (during closed loop) after the engine is warmed.

If within specifications, go to Step 3.
If not within specifications, refer to DTC P0170 - Fuel Trim Malfunction.

STEP 3. Using scan tool MB991502, check data list item 82: Short-Term Fuel Trim.
1. Start the engine and run at idle.
2. Set scan tool MB991502 to the data reading mode for item 82, Short-Term Fuel Trim.
- The fuel trim should be between -10 and +10 when the load is 2,500 r/min (during closed loop) after the engine is warmed.

If within specifications, go to Step 4.
If not within specifications, refer to DTC P0170 - Fuel Trim Malfunction.

STEP 4. Check each ignition coil spark.
1. Check each ignition coil spark.
2. Remove the spark plug and connect to the spark plug cable.
3. Ground the spark plug side electrode securely.
4. When the engine is cranked, the spark plug should spark.
If correct, go to Step 7. If incorrect, go to Step 5.

STEP 5. Check the spark plugs.
1. Check the plug is not burned out, that the insulator plug is not damaged, and that there are no carbon deposits.
2. If cleaning is required due to carbon deposits, etc., clean using a plug cleaner or wire brush, etc.
3. Check the plug gap using a plug gap gauge.
Standard value: 1.0 - 1.1 mm (0.039 - 0.043 inch)
If within specifications, go to Step 6.
If not within specifications, repair or replace the faulty spark plug. Then go to Step 13.

STEP 6. Check the spark plugs cable.
1. Check the cap and coating for cracks
2. Measure the resistance.
Limit: maximum 22 kohms
If within specifications, refer to INSPECTION PROCEDURE 34 - Ignition Circuit System.
If not within specifications, replace the faulty spark plug cable. Then go to Step 13.

STEP 7. Check the injectors.
1. Disconnect each injector connector.

2. Measure resistance between injector side connector 1 and 2 at each injector.
Standard value: 13 - 16 ohms [at 20°C (68°F)]
If within specifications, go to Step 8.
If not within specifications, replace the faulty injector. Then go to Step 13.

STEP 8. Check harness connectors B-01, B-02, B-05, B-06 at the injector for damage.
If harness connectors B-01, B-02, B-05, B-06 are in good condition, go to Step 9.
If harness connectors B-01, B-02, B-05, B-06 are damaged, repair or replace them.
Refer to Harness Connector Inspection. Then go to Step 13.

STEP 9. Check harness connector C49 at the ECM or harness connector C-50 at the PCM for damage.
If harness connector C-49 or C-50 is in good condition, go to Step 10.
if harness connector C-49 or C-50 is damaged, repair or replace it.
Refer to Harness Connector Inspection. Then go to Step 13.

STEP 10. Check the harness wires between injector connectors B-01, B-02, B-05, B-06 and ECM connector C-49 or PCM connector C-50 .
If the wires between injector connectors B-01 B-02, B-05, B-06 and ECM connector C-49 or PCM connector C-50 are not damaged, go to Step 11.
If the wires between injector connectors B-01, B-02, B-05, B-06 and ECM connector C-49 or PCM connector C-50 are damaged, repair them. Then go to Step 13.

STEP 11. Check the following items.
1. Check the following items, and repair or replace the defective component.
a. Check for skipped timing belt teeth.
b. Check compression.
c. EGR valve failed.

Then go to Step 12.

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 P0300 is not output, the inspection is complete.
If DTC P0300 is 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 P0300 does not reset.