P0308
DTC P0308 CYLINDER 8 MISFIRE DETECTEDCIRCUIT DESCRIPTION
DTC Detection 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 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 continuously flash 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 and could cause emissions deterioration, the ECM illuminates the MIL and set a DTC.
HINT: In some cases, several DTCs for misfired cylinders (DTCs P0301 to P0308) are recorded but the random/ multiple cylinder misfire DTC (P0300) is not recorded.This is an indication that the misfires were detected and recorded at different times. Random misfire codes are recorded only when several misfires occur at the same time.
Reference: Inspection using an oscilloscope.
With the engine idling, check the waveform between terminals #10 to #80 and E1 of the ECM connectors.
The correct waveform is as shown.
MONITOR DESCRIPTION
Monitor Strategy:
Typical Enabling Conditions Part 1:
Typical Enabling Conditions Part 2:
Typical Malfunction Thresholds:
The ECM illuminates the MIL (2 trip detection logic.as follows (DTC is stored after 2 trip detection):
- The misfiring rate exceeds a threshold value and could cause emissions deterioration.
- During the first 1,000 crankshaft revolutions after engine starts, an excessive misfire rate (approximately 20 to 50 misfire per 1,000 crankshaft revolutions) occurs once.
- An excessive misfire rate (approximately 20 to 60 misfire per 1,000 crankshaft revolutions) occurs 4 times.
The ECM flashes continuously the MIL (MIL flashes immediately) as follows (DTC is stored after 2 trip detection):
- Within 200 crankshaft revolutions at a high rpm, the threshold for "percent of misfire causing catalyst damage" is reached once.
- Within 200 crankshaft revolutions at a normal rpm, the threshold for "percent of misfire causing catalyst damage" is reached 3 times.
HINT: MIL flashing is stopped when the misfire is less than 72 per 170 revolutions or less than 85 per 200 revolutions.
CONFIRMATION DRIVING PATTERN
a. Connect the hand-held tester to the DLC3.
b. Record the DTC and freeze frame data.
c. Set check mode on the hand-held tester.
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 while using the DATA LIST's MISFIRE RPM and MISFIRE LOAD menu items to keep track of the vehicle's engine speed, load and its surrounding range.
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 force output of the DTC, it is necessary to drive with MISFIRE RPM and MISFIRE LOAD selected in the DATA LIST for the period of time in the chart. Do not turn the ignition switch OFF. Turning the ignition switch OFF switches the diagnosis system from check mode to normal mode and all DTCs, freeze frame data and other data are erased.
f. Check if there is misfire or not by monitoring DTC and the freeze frame data. After that, record the DTCs, freeze frame data and misfire counter data.
g. Turn the ignition switch OFF and wait for at least 5 seconds.
Wiring Diagram:
Wiring Diagram:
Step 1:
Step 2 - 4:
Step 5 - 6:
Step 7 - 9:
Step 10:
Step 11 - 12:
Step 13 - 16:
Step 17 - 18:
INSPECTION PROCEDURE
HINT:
- If DTCs other than misfire DTCs are output simultaneously, troubleshoot the non-misfire DTCs first.
- Read freeze frame data using the hand-held tester. Freeze frame data records the engine conditions when a malfunction is detected.When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was LEAN or RICH, and other data from the time the malfunction occurred.
- If the misfire does not occur when the vehicle is brought to the workshop, the misfire can be confirmed by reproducing the conditions recorded in the freeze frame data. Also, after finishing repairs, confirm that no misfire occurs (see confirmation driving pattern).
- On 6 and 8 cylinder engines, cylinder-specific misfire fault codes are disabled at high engine speeds. If the misfire starts in a high engine speed range or the misfire occurs only in a high engine speed area, only general fault code P0300 will be stored.
When only P0300 is stored:
1. Erase the general misfire fault code from the hand-held tester.
2. Start the engine and drive the confirmation pattern (see confirmation driving pattern).
3. Read the value of the misfire ratio for each cylinder. Or, check if a DTC was output.
4. Perform repairs on the cylinder that has a high misfire ratio. Or repair the cylinder indicated by any output DTCs.
5. After finishing repairs, drive the confirmation pattern again and confirm that no misfire occurs.
- If SHORT FT #1, LONG FT #1, SHORT FT #2 or LONG FT #2 in the freeze frame data is 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), a misfire is only possible during engine warm-up.
- If the misfire cannot be reproduced, the cause may be: 1) low fuel in the vehicle, 2) improper fuel in the vehicle, 3) a contaminated ignition plug, or 4) another problem.
- Be sure to check the value on the misfire counter after repairs.
CHECK FOR INTERMITTENT PROBLEMS
HINT: Inspect the vehicle's ECM using check mode. Intermittent problems are easier to detect when the hand-held tester is in check mode. In check mode, the hand-held tester 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
b. Set the check mode
c. Perform a simulation test.
d. Check the connector and terminal
e. Wiggle the harness and the connector