P0303
DTC P0303 Cylinder 3 Misfire DetectedCIRCUIT DESCRIPTION
DTC Detection Condition:
When a misfire occurs in the engine, high concentrations of hydrocarbons (HC) enter the exhaust gas. If this HC concentration is extremely high, there could be an increase in exhaust emission levels. High concentrations of HC can also cause temperature of the catalyst to increase, possibly damaging the catalyst. To prevent this increase in emissions and to limit the possibility of thermal damage, the ECM monitors the misfire rate. When the temperature of the catalyst 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 misfiring cylinders and the CKP sensor is used to measure variations in the crankshaft rotation speed. The misfire counter increments when crankshaft rotation speed variations exceed threshold values.
If the misfire rate exceeds the threshold level, and could cause emission deterioration, the ECM illuminates the MIL and set a DTC.
HINT: When codes for a misfiring cylinder are recorded repeatedly but no random misfire code is recorded, it indicates that the misfires have been detected and recorded at different times.
Reference: INSPECTION USING OSCILLOSCOPE
With the engine idling, check the waveform between terminals #1 to #4 and E01 of the ECM connectors.
HINT: The correct waveform is as shown.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
The ECM illuminates the MIL if the misfiring rate exceeds a threshold value and could cause emissions deterioration.
The ECM will illuminate the MIL when the percent misfire exceeds the specified limit per 1,000 engine revolutions. One occurrence of excessive misfire during engine start will set the MIL. Four occurrences are required to set the MIL 1,000 revolutions after engine start.
(2 trip detection logic)
The MIL blinks when "percent misfire causing catalyst damage" per 200 revolution is met 3 times (1 time if the engine rpm is in high speed range).
(MIL blinks immediately)
Wiring Diagram:
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
a. Connect the hand-held tester to the DLC3.
b. Record DTCs and freeze frame data.
c. Set check mode using the hand-held tester.
d. Read the value on the misfire counter for each cylinder when idling. If the value is displayed on the misfire counter, skip the following procedure of confirmation driving.
e. Drive the vehicle several times with the engine speed, load and its surrounding range shown at MISFIRE RPM, MISFIRE LOAD in the DATA LIST.
If you have no hand-held tester, turn the ignition switch to OFF after the symptom is simulated once. Then repeat the simulation process again.
HINT: In order to record the misfire DTC, it is necessary to drive with MISFIRE RPM, MISFIRE LOAD in the DATA LIST for the period of time indicated in the table. Do not turn the ignition switch to OFF. Turning the ignition switch to OFF switches the diagnosis system from check mode to normal mode and all DTCs, freeze frame data and other data are erased.
f. Check whether a misfire occurs or not by monitoring DTCs and freeze frame data. After that, record the DTCs, freeze frame data and misfire counter data.
g. Turn the ignition switch to OFF and wait for at least 5 seconds.
INSPECTION PROCEDURE
Step 1 - 3:
Step 4:
Step 5:
Step 6:
Step 7:
Step 7 (Continued) - 9:
Step 10:
Step 10 (Continued) - 14:
Step 15 - 17:
Step 18 - 19:
HINT:
- If DTCs other than misfire DTCs are set simultaneously, first perform troubleshooting for them.
- Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data record 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 occur when the vehicle is brought to the workshop, the misfire can be confirmed by reproducing the conditions of the freeze frame data. Also, after finishing the repair, confirm that there is no misfire (see confirmation driving pattern).
- On 6 and 8 cylinder engines, the ECM intentionally does not set the specific misfiring cylinder DTCs at high engine speed. If misfires occur only in high engine speed areas, only DTC P0300 is set. When only DTC P0300 is stored:
1. Clear the DTC.
2. Conduct the confirmation driving pattern (see confirmation driving pattern).
3. Read the misfire rate of each cylinder or DTCs.
4. Repair the cylinder(s) that has a high misfire rate, or is indicated by the DTC.
5. After finishing repairs, conduct the confirmation driving pattern again in order to confirm that no misfire occurs.
- When one of SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 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 COOLANT TEMP in the freeze frame data is less than 75 °C (167 °F), the misfires have occurred only during engine warm-up.
- If the misfire cannot be reproduced, the following reasons may apply: 1) the vehicle has low fuel, 2) improper fuel is used, 3) the ignition plug is contaminated, or 4) another problem.
- Be sure to check the value on the misfire counter after the repair.
CHECK FOR INTERMITTENT PROBLEMS
HINT:
Hand-held tester only:
Inspect the vehicle's ECM using check mode. Intermittent problems are easier to detect with the hand-held tester when the ECM is in check mode. In check mode, the ECM uses 1trip detection logic, which is more sensitive to malfunctions than normal mode (default) that uses 2trip detection logic.
a. Clear DTCs.
b. Switch the ECM from normal mode to check mode using a hand-held tester.
c. Perform a simulation test.
d. Check and wiggle the harness(es), the connector(s) and terminal(s).