P0300
DTC P0300 Random/Multiple Cylinder 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 emission levels. High concentrations of HC can also cause the temperature of the catalyst to increase, possibly damaging the catalyst. To prevent this increase 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 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 counter increments when crankshaft rotation speed variations exceed threshold values.
If the misfiring rate exceeds the threshold value, which could cause emissions deterioration, the ECM illuminates the MIL.
HINT: When several 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 the oscilloscope.
With the engine idling, check the waveform between terminals #10 to #60 and E01 of the ECM connectors.
HINT: The correct waveform is as shown in the illustration.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions:
Typical Malfunction Thresholds:
The ECM illuminates the MIL (2 trip detection logic) if:
The ECM will illuminate the MIL when the percentage of 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.
The ECM blinks the MIL (the MIL blinks immediately) if:
- Within 200 engine revolutions at a high rpm, the threshold for "percentage of misfire causing catalyst damage" is reached 1 time.
- Within 200 engine revolutions at a normal rpm, the threshold for "percentage of misfire causing catalyst damage" is reached 3 times.
Wiring Diagram:
CONFIRMATION DRIVING PATTERN
a. Connect the hand-held tester to the DLC3.
b. Record DTC and the freeze frame data.
c. Use the hand-held tester to set 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 surrounding range shown as ENGINE SPD, CALC LOAD in the freeze frame data or 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 once. Then repeat the simulation process again.
HINT: In order to memorize the DTC of misfire, it is necessary to drive around 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 mode to normal mode, and all DTCs, etc., are erased.
f. Check if there is misfire, the DTC and the freeze frame data. Record the DTC's, freeze frame data and misfire counter data.
g. Turn the ignition switch OFF and wait for at least 5 seconds.
INSPECTION PROCEDURE
Step 1 - 3:
Step 4:
Step 5:
Step 6 - 7:
Step 8 - 11:
Step 12 - 15:
Step 16 - 17:
Step 18 - 19:
HINT:
- If DTCs besides misfire DTCs are memorized simultaneously, troubleshoot the non-misfire DTCs first.
- If the misfire does not occur when the vehicle is brought to the workshop, the 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 confirmation driving pattern).
- On 6 or 8 cylinder engines, misfiring cylinder identification is disabled at high engine speed and only a general misfire fault code P0300 is stored instead of a cylinder specific misfire fault code (P0301 to P0308).
If the misfire starts in a high engine speed area or the misfire occurs only in a high engine speed area, only code P0300 may be stored.
When only a general misfire fault code like P0300 is stored:
- Erase the general misfire fault code using the hand-held tester or OBD II scan tool.
- Start the engine and drive the confirmation pattern.
- Read the value of the misfire ratio for each cylinder. Or read the DTC.
- Repair the cylinder that has a high misfire ratio. Or repair the cylinder indicated by the DTC.
- After finishing repairs, drive the confirmation pattern again and confirm that no misfire occurs.
- 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 becoming 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 engine warm-up.
- If the misfire cannot be reproduced, the following reasons may apply: 1) the vehicle has low fuel, 2) improper fuel is being used, or 3) the ignition plug is contaminated.
- Be sure to check the value on the misfire counter after the repair.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
Inspect the vehicle's ECM using check mode. Intermittent problems are easier to detect when the ECM is in check mode with hand-held tester. In check mode, the ECM uses 1 trip detection logic, which has a higher sensitivity to malfunctions than normal mode (default), which uses 2 trip detection logic.
a. Clear the DTCs (see step 2).
b. Set the check mode (see step 3).
c. Perform a simulation test.
d. Check the connector and terminal.
e. Wiggle the harness and connector.