Troubleshooting
DTC P0303 Cylinder 3 Misfire DetectedCIRCUIT DESCRIPTION
DTC Detecting Condition:
Misfire: The ECM uses the crankshaft position sensor and camshaft position sensor to monitor changes in the crankshaft rotation for each cylinder.
The ECM counts the number of times the engine speed change rate indicates that misfire has occurred. And when the misfire rate equals or exceeds the count, which indicates that the engine condition has deteriorated and the MIL lights up.
If the misfire rate is extremely high, the driving conditions will cause catalyst to overheat and the MIL blinks when misfiring occurs.
HINT: When codes for a misfiring cylinder are recorded repeatedly but no random misfire code is included, 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 to the DLC3.
b. Record DTC and the freeze frame data.
c. Use the hand-held tester to set to the check mode.
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 with the ENGINE SPD, CALC LOAD in the freeze frame data or the MISFIRE RPM, MISFIRE LOAD in the data list.
If you have no hand-held tester, turn the ignition switch OFF after the symptom is simulated the first time.
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.
- Take care not to turn the ignition switch OFF. Turning the ignition switch OFF switches the diagnosis system from check (test) mode to normal mode. So all DTCs, etc., are erased.
f. Check whether misfire occurs or not by monitoring DTC and the freeze frame data. After that, record them.
g. Turn the ignition switch OFF and wait at least 5 seconds.
Step 1:
Step 2 - 4:
Step 5:
Step 6 - 7:
Step 8 - 9:
Step 10 - 13:
Step 14 - 17:
Step 18 - 19:
Hand-Held Tester only:
Step 1:
Step 2 - 3:
Step 4:
Step 5 - 6:
Step 7 - 8:
Step 9 - 12:
Step 13 - 16:
OBD II scan (Excluding Hand-held Tester)
INSPECTION PROCEDURE
HINT:
- If is case that DTC besides misfire is memorized simultaneously, first perform the troubleshooting for them.
- Read freeze frame data using OBD II scan tool or hand-held tester. Because freeze frame date records the engine conditions when the malfunction is detected. When troubleshooting, it is useful to determine 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.
- When the vehicle is brought to the workshop and the misfire is not occurred, misfire can be confirmed by reproducing the condition of freeze frame data. Also, after finishing the repair, confirm that there is no misfire (See confirmation driving pattern).
- On 6 and 8 cylinder engines, misfiring cylinder identification is disabled at high engine speed and only an general misfire fault code P0300 is stored instead of a cylinder specific misfire fault code (i. e., P0301 - P0308). Under the following conditions, only P0300 code may be stored.
Misfire starts in the high engine speed area or misfire occurs only in the high engine speed area. The refore, when a general misfire fault code (i.e., P0300) is only stored, erase the DTCs with the hand- held tester or OBD II scan tool. Start the engine and drive the confirmation pattern (See the CONFIRMATION DRIVING PATTERN) and read the value of the misfire ratio for each cylinder (or DTC). Perform the repair correspond to the high misfire ratio cylinder (or the misfiring cylinder indicated by DTC). After completing the repair, confirm no misfire is occurring by driving the confirmation pattern.
- When either of SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data is beside 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 while warmed up.
- In the case that misfire cannot be reproduced, the reason may be because of the driving with lack of fuel, the use of improper fuel, a stain of the ignition plug, and etc.
- Be sure to check the value on the misfire counter after the repair.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
By putting the vehicle's ECM in check mode, 1 trip detection logic is possible instead of 2 trip detection logic and sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.
1. Clear the DTC.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.
CONFIRMATION DRIVING PATTERN
a. Connect the hand-held tester to the DLC3.
b. Switch the hand-held tester from the normal mode to the check mode.
c. Start the engine and let the engine idle for 100 sec. or more.
d. Drive the vehicle at 40 km/h (24 mph) or more for 20 sec. or more.
e. Let the engine idle for 20 sec. or more.
f. Let the engine idle for 30 sec.
HINT: If a malfunction exists, the MIL will light up during step (f).
NOTE: If the conditions in this test are not strictly followed, detection of the malfunction will not be possible.
If you do not have a hand-held tester, turn the ignition switch OFF after performing steps (c) to (f),then perform steps (c) to (1) again.