Troubleshooting

DTC P0303 CYLINDER 3 MISFIRE DETECTED

CIRCUIT DESCRIPTION

DTC Detection Condition:

When a misfire occurs in the engine, hydrocarbons (HC) enter the exhaust gas 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 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 and 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 oscilloscope

Oscilloscope Waveform:

With the engine idling, check the waveform between terminals #10 to #40 and E01 of the ECM connectors.

HINT: The correct waveform is as shown.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

The ECM illuminates the MIL (2 trip detection logic) if:
- The percent misfire exceeds the specified limit per 1,000 engine revolutions. One occurrence of excessive misfire during engine start will set the MIL. After engine start, four occurrences of excessive misfire set the MIL.

The ECM blinks the MIL (immediately) if:
- The threshold for percent of misfire causing catalyst damage is reached 1 time in 200 engine revolutions at a high rpm, and 3 times in 200 engine revolutions at a normal rpm.
- The threshold for percent of misfire causing catalyst damage is reached

Wiring Diagram:

CONFIRMATION DRIVING PATTERN

a. Connect the hand-held tester to the DLC3.
b. Record DTCs and the freeze frame data.
c. Switch the ECM from normal mode to check mode using 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 with an engine speed (ENGINE SPD), engine load (CALC LOAD) and other data stored in the freeze frame data.
If you have no hand-held tester, turn the power switch OFF after the symptom is simulated once. Then repeat the simulation process again.

HINT: In order to memorize the misfire DTCs, it is necessary to drive with MISFIRE RPM and MISFIRE LOAD in the DATA LIST for the period of time in the chart below. Take care not to turn the power switch OFF. Turning the power 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 a misfire, DTC and the freeze frame data. Record DTCs, freeze frame data and misfire counter data.
g. Turn the power switch OFF and wait at least for 5 seconds.

Step 1 - 3:

Step 4:

Step 5 - 6:

Step 7:

Step 7 (Continued) - 9:

Step 10:

Step 11 - 14:

Step 15 - 17:

Step 18 - 19:

INSPECTION PROCEDURE

HINT:
- If DTCs besides misfire DTCs are memorized simultaneously, troubleshoot the non-misfire DTCs first.
- Read freeze frame data using the intelligent tester II. Freeze frame data records the engine condition when 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 condition of the freeze frame data. Also, after finishing repairs, confirm that there is no misfire (see confirmation driving pattern).
- When either of SHORT FT #1 and LONG FT #1 in the freeze frame data is over 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 during engine warm-up.
- If the misfire cannot be reproduced, the reason may be because of the driving the vehicle with lack of fuel, use of improper fuel, a stain on the ignition plug, etc.
- Be sure to check the value on the misfire counter after repairs.