P0303
DTC P0300 Random / Multiple Cylinder Misfire DetectedDTC P0301 Cylinder 1 Misfire Detected
DTC P0302 Cylinder 2 Misfire Detected
DTC P0303 Cylinder 3 Misfire Detected
DTC P0304 Cylinder 4 Misfire Detected
DESCRIPTION
DTC Detection Condition:
When the engine misfires, high concentrations of hydrocarbons (HC) enter the exhaust gas. Extremely high HC concentration levels can cause increases in exhaust emission levels. High concentrations of HC can also cause increases in the Three-Way Catalytic Converter (TWC) temperature, which may cause damage to the TWC. To prevent these increases in emissions and to limit the possibility of thermal damage, the ECM monitors the misfire rate. When the temperature of the TWC reaches the point of thermal degradation, the ECM blinks the MIL. To monitor misfires, the ECM uses both the Camshaft Position (CMP) sensor and the Crankshaft Position (CKP) sensor. The CMP sensor is used to identify any misfiring cylinders and the CKP sensor is used to measure variations in the crankshaft rotation speed.
Misfires are counted when the crankshaft rotation speed variations exceed predetermined thresholds. If the misfire exceeds the threshold levels, and could cause emission deterioration, the ECM illuminates the MIL and sets a DTC.
HINT: When the DTCs for misfiring cylinders are recorded repeatedly but no random misfire DTC is recorded, it indicates that the misfires have been set and recorded at different times. Random misfire codes are recorded only when several misfires occur at the same time.
Reference: Inspection using the oscilloscope
With the engine idling, check the waveform between terminals #10 to #40 and E01 of the ECM connectors.
HINT: The correct waveform is as given.
MONITOR DESCRIPTION
Monitor Strategy (part 2):
Typical Enabling Conditions:
The ECM illuminates the MIL and sets a DTC when either one of the following conditions, which could cause emission deterioration, is detected. (2 trip detection logic.)
- Within the first 1,000 crankshaft revolutions of the engine starting, an excessive misfiring rate (approximately 20 to 50 misfires per 1,000 crankshaft revolutions) occurs once.
- After the first 1,000 crankshaft revolutions, an excessive misfiring rate (approximately 20 to 60 misfires per 1,000 crankshaft revolutions) occurs 4 times in sequential crankshaft revolutions.
The ECM flashes the MIL and sets a DTC when either one of the following conditions, which could cause the Three-Way Catalytic Converter (TWC) damage, is detected (2 trip detection logic).
- In every 200 crankshaft revolutions at a high engine rpm, the threshold misfiring percentage is recorded once.
- In every 200 crankshaft revolutions at a normal engine rpm, the threshold misfiring percentage is recorded 3 times.
CONFIRMATION DRIVING PATTERN
a. Connect the intelligent tester to the DLC3.
b. Turn the ignition switch ON and turn the tester ON.
c. Record the DTC(s) and freeze frame data.
d. Using the tester, switch the ECM from normal mode to check mode.
e. Read the misfire counts of each cylinder (CYL #1 to #4) with the engine in an idling condition. If any misfire count is displayed, skip the following confirmation driving pattern.
f. Drive the vehicle several times with the conditions, such as engine rpm and engine load, shown in MISFIRE RPM, MISFIRE LOAD in the DATA LIST.
HINT: In order to store misfire DTCs, it is necessary to drive the vehicle for the period of time shown in the table given, with the MISFIRE RPM and MISFIRE LOAD in the DATA LIST.
g. Check whether misfires have occurred by checking DTCs and freeze frame data.
HINT: Do not turn the ignition switch OFF until the stored DTC(s) and freeze frame data have been recorded. When the ECM returns to normal mode (default), the stored DTC(s), freeze frame data and other data will be erased.
h. Record the DTC(s), freeze frame data and misfire counts.
i. Turn the ignition switch OFF and wait for at least 5 seconds.
Wiring Diagram:
Step 1:
Step 1(Continued)-4:
Step 4(Continued)-6:
Step 6(Contiuned)-9:
Step 9(Continued)-11:
Step 11(Continued)-16:
Step 16(Continued)-17:
INSPECTION PROCEDURE
HINT:
- If any DTCs other than the misfire DTCs are output, troubleshoot those DTCs first.
- Read freeze frame data using the intelligent tester. Freeze frame data records the engine condition when malfunctions are detected. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
- If the misfire does not recur when the vehicle is brought to the workshop, reproduce the conditions stored in the freeze frame data.
- If the misfire still cannot be reproduced even though the conditions stored in the freeze frame data have been duplicated, one of the following factors is considered to be a possible cause of the problem:
a. The in the fuel tank is low.
b. Improper fuel is used.
c. The ignition plugs have been contaminated.
d. The problem is complex.
- After finishing repairs, check the misfire counts of the cylinders (CYL #1, #2, #3 and #4).
- Be sure to confirm that no misfiring cylinder DTCs are set again by conducting the confirmation driving pattern after repairs.
- For 6 and 8 cylinder engines, the ECM intentionally does not set the specific misfiring cylinder DTCs at high engine RPM. If misfires occur only in high engine RPM areas, only DTC P0300 is set. In the event of DTC P0300 being present, perform the following operations:
a. Clear the DTC.
b. Start the engine and conduct the confirmation driving pattern.
c. Read the misfiring rates of each cylinder or DTC(s) using the tester.
d. Repair the cylinder(s) that has a high misfiring rate or is indicated by the DTC.
e. After finishing repairs, conduct the confirmation driving pattern again in order to verify that DTC P0300 is not set.
- When one of SHORT FT #1, LONG FT #1 in the freeze frame data is outside the range of +-20%, the air-fuel ratio may be rich (-20% or less) or lean (+20% or more).
- When the COOLANT TEMP in the freeze frame data is less than 75 degrees C (167 degrees F), the misfires have occurred only while warming up the engine.