Troubleshooting
DTC P0303 Cylinder 3 Misfire DetectedDTC Detection Condition:
CIRCUIT DESCRIPTION
Misfire: The ECM uses the crankshaft position sensor and camshaft position sensor to monitor changes in the crankshaft rotation of each cylinder.
The ECM counts the number of times of indicating that misfire has occurred, by using the engine speed change rate. And when the misfire rate equals to or exceeds the count of indicating that the engine condition has deteriorated, the MIL lights up.
If the misfire rate is very high and the driving conditions cause the catalyst to overheat, the MIL shows an occurence of misfire by blinking.
HINT: When the 2 or more codes of a misfiring cylinder are recorded repeatedly but no random misfire code is recorded, it indicates that the misfires were detected and recorded at different times.
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
a. Connect the hand-held tester or OBD II scan tool.
b. Record the DTC and freeze frame data.
c. Use the hand-held tester to set to the check mode.
d. Drive the vehicle several times with the engine speed, load and its surrounding range shown with the ENGINE SPD, CALC LOAD in the freeze frame data or the MISFIRE RPM, MISFIRE LOAD in the data list. Without hand-held tester, turn the ignition switch OFF after the symptom is simulated once. Then repeat the simulation process again.
HINT: In order to memorize DTC of misfire, it is necessary to drive around the MISFIRE RPM, MISFIRE LOAD in the data list for the following period of time in the data list.
e. Check whether there is misfire or not by monitoring the DTC and freeze frame data and then record them.
f. Turn the ignition switch OFF and wait at least 5 seconds.
Step 1 - 3:
Step 4 - 5:
Step 5 (Continued) - 8:
INSPECTION PROCEDURE
HINT:
- In case that DTC's besides misfire are memorized simultaneously, first perform the troubleshooting for them.
- Read freeze frame data using hand-held tester or OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.
- If the misfire does not occur when the vehicle is brought to the workshop, misfire can be confirmed by reproducing the condition of the freeze frame data. Also, after finishing the repair, confirm that there is no misfire (See the confirmation driving pattern).
- When either of SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data is over the range of ±20 %, there is a possibility that the air-fuel ratio is inclining either to "RICH" (-20 % or less) or "LEAN" (+20 % or more).
- When COOLANT TEMP in the freeze frame data is less than 80 °C (176 °F), there is a possibility of misfire only during warming up the engine.
- In case that the misfire cannot be reproduced, the reason may be because of driving with lack of fuel, a use of improper fuel, a stain of ignition plug, and etc.