Troubleshooting
DTC P0304 Cylinder 4 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 indicating that the engine condition has deteriorated, the MIL lights up.
If the misfire rate is high enough and the driving conditions will cause catalyst overheating, the MIL blinks when misfiring occurs.
HINT: When the 2 or more codes for 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 to the DLC3.
b. Record DTC and the 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.
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 period of time.
e. Check whether there is misfire or not by monitoring DTC and the freeze frame data. After that, record them.
f. 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:
INSPECTION PROCEDURE
HINT:
- If is the case that DTC besides misfire is memorized simultaneously, first perform the troubleshooting for them.
- Read freeze frame data using hand-held tester or OBD II scan tool. Because freeze frame data records the engine conditions when the malfunction is detected, when troubleshooting it is useful for determining whether the vehicle was running or stopped, the engine warmed up or not, the air-fuel ratio 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 or freeze frame data. Also, after finishing the repair, confirm that there is no misfire. (See the 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 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. Therefore, when a general misfire fault code (i.e., P0300) is only stored, erase the DTCs after read freeze frame data 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 besides 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 or misfire only during warming up.
- In the case that misfire cannot be reproduced, the reason may be because of the driving with lack or fuel, the use of improper fuel, a stain of ignition plug, and etc.
- Be sure to check the value on the misfire counter after the repair.
CHECK FOR INTERMITTENT PROBLEMS
HINT:
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 the sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.
a. Clear the DTC.
b. Set the check mode.
c. Perform a simulation test.
d. Check the connector and terminal.
e. Handle the connector.