DTC P0300: Random/Multiple Cylinder Misfire Detected

TECHNICAL DESCRIPTION

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

DESCRIPTIONS OF MONITOR METHODS

MONITOR EXECUTION

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)

Not applicable

Sensor (The sensor below is determined to be normal)

Camshaft position sensor
Mass airflow sensor
Engine coolant temperature sensor
Intake air temperature sensor
Barometric pressure sensor
Throttle position sensor

DTC SET CONDITIONS

Logic Flow Chart

Check Conditions

Engine speed is between 438 and 6,500 r/min.
Engine coolant temperature is more than -10°C (14°F).
Barometric pressure is more than 76 kPa (22.4 in.Hg).
The engine load is with in the positive torque load.
Adaptive learning is complete for the vane which generates a crankshaft position signal.
While the engine is running, excluding sudden acceleration/deceleration and fuel shut-off operation.

Judgement Criterion (change in the angular acceleration of the crankshaft is used for misfire detection)

Misfire has occurred more frequently than allowed during the last 200 revolutions [when the catalyst temperature is more than 1,000°C (1,832°F)].

Misfire has occurred in 2.0 percent or more of the last 1,000 revolutions (corresponding to 1.5 times the limit of emission standard).

FAIL-SAFE AND BACKUP FUNCTION

The supply of fuel to the misfiring cylinder can possibly be cut.

OBD-II DRIVE CYCLE PATTERN

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

Included air due to lack of fuel.
Ignition system related part(s) failed.
Poor crankshaft position sensor.
Incorrect air/fuel ratio.
Low compression pressure.
Skipping of timing chain teeth.
ECM failed.

DIAGNOSIS

Required Special Tools:

MB991958: Scan Tool (M.U.T.-III Sub Assembly)

MB991824: V.C.I.
MB991827: USB Cable
MB991910: Main Harness A

STEP 1. Check whether air is included due to the lack of fuel or not.

Check whether users have experienced the lack of fuel or not.

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

	Erase the diagnosis codes to finish the check.

	Go to Step 2.

STEP 2. Using scan tool MB991958, check data list item 2: Crankshaft Position Sensor.

caution

To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

(1)Connect scan tool MB991958 to the data link connector.
(2)Start the engine and run at idle.
(3)Set scan tool MB991958 to the data reading mode for item 2, Crankshaft Position Sensor.

The tachometer and engine speed indicated on the scan tool should match.

(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the sensor operating properly?

Go to Step 3.

Refer to, DTC P0335 - Crankshaft Position Sensor Circuit

STEP 3. Using scan tool MB991958, check data list item 26: Long-Term Fuel Trim.

(1)Start the engine and run at idle.

(2)Set scan tool MB991958 to the data reading mode for item 26, Long-Term Fuel Trim.

The fuel trim should be between -12.5 and +12.5 percent when the engine is 2,500 r/min (during closed loop) after the engine is warmed.

(3)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the specification normal?

	Go to Step 4.

	Refer to DTC P0171 - System too Lean , DTC P0172 - System too Rich .

STEP 4. Using scan tool MB991958, check data list item 28: Short-Term Fuel Trim.

(1)Start the engine and run at idle.

(2)Set scan tool MB991958 to the data reading mode for item 28, Short-Term Fuel Trim.

The fuel trim should be between -25 and +25 percent when the engine is 2,500 r/min (during closed loop) after the engine is warmed.

(3)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the specification normal?

	Go to Step 5.

	Refer to DTC P0171 - System too Lean , DTC P0172 - System too Rich .

STEP 5. Visual check of ignition spark.

(1)Remove the spark plug and install it to the ignition coil.
(2)Connect the ignition coil connector.
(3)Remove all injector connector.
(4)At the engine start, check each spark plug produces a spark.

Q. Did it spark?

Go to Step 7.

Go to Step 6.

STEP 6. Check the spark plugs.

Refer to GROUP 16, Ignition System - On-vehicle Service - Spark Plug Check And Cleaning

Q. Is the spark plug normal?

	Refer to Symptom Procedures 25 - Ignition Circuit System .

	Replace the faulty spark plug. Then go to Step 9.

STEP 7. Check the following items.

(1)Check the following items, and repair or replace the defective component.

Check for skipped timing chain teeth.
Check compression.

Q. Are there any abnormalities?

	Repair or replace it. Then go to Step 9.

	Go to Step 8.

STEP 8. Check the trouble symptoms.

(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 14

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0300 set?

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 9.

	It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .

STEP 9. Test the OBD-II drive cycle.

(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 14

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0300 set?

	Retry the troubleshooting.

	The inspection is complete.