Troubleshooting
DTC P0302 Cylinder 2 Misfire DetectedCIRCUIT DESCRIPTION
DTC Detecting Condition:
When a misfire occurs in the engine, hydrocarbons (HC) enter the exhaust in high concentrations. If this HC concentration is high enough, there could be an increase in exhaust emissions levels. High concentrations of HC can also cause to temperature of the catalyst to increase, possibly damaging the catalyst. To prevent increases in emissions and limit the possibility of thermal damage, the ECM monitors the misfire rate. When the temperature of the catalyst reaches a point of thermal degradation, the ECM will blink the MIL. For monitoring a misfire, the ECM uses both the camshaft position sensor and the crankshaft position sensor. The camshaft position sensor is used to identify misfiring cylinders and the crankshaft position sensor is used to measure variations in the crankshaft rotation speed. The misfire is counted when crankshaft rotation speed variations exceed threshold values.
If the misfiring rate exceeds the threshold value and could cause emissions deterioration, the ECM illuminates the MIL.
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.
MONITOR DESCRIPTION
Monitor Description:
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
The ECM illuminates the MIL (2 trip detection logic) if:
- The misfiring rate exceeds a threshold value and could cause emissions deterioration.
- During the first 1,000 engine revolutions after the engine starts, an excessive misfire rate (approximately 20 to 50 misfire per 1,000 engine revolutions) occurs 1 time.
- After the first 1,000 engine revolutions after the engine starts, an excessive misfire rate (approximately 20 to 50 misfire per 1,000 engine revolutions) occurs 4 times. The ECM blinks the MIL (MIL blinks immediately) if:
- Within 200 engine revolutions at a high rpm, the threshold for "percent of misfire causing catalyst damage" is reached 1 time.
- Within 200 engine revolutions at a normal rpm, the threshold for "percent of misfire causing catalyst damage" is reached 3 time.
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
a. Connect the OBD II scan tool or hand-held tester.
b. Record the 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 MISFIRE RPM, MISFIRE LOAD in the data list for the given 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 - 2:
Step 3:
Step 4 - 5:
Step 5 (Continued) - 9:
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 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 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 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 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
Therefore, when a general misfire fault code (i.e., P0300) is only stored, start the engine and drive the confirmation pattern (See the CONFIRMATION DRIVING PATTERN) and read the value of the misfire ratio for each cylinder. Perform the repair correspond to the high misfire ratio cylinder. 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.