P0303

DTC P0303 CYLINDER 3 MISFIRE DETECTED

1. OUTLINE OF DIAGNOSIS
Detect the presence of misfire occurrence. (Revolution fluctuation method)

Monitoring misfire which influences exhaust deterioration (1.5 times of FTP) and catalyst damage is made obligatory by the law. Misfire affecting these two has three patterns below.
- Intermittent misfire (The same cylinder misfires in random, or different cylinders misfire in random.): FTP 1.5 times misfire
- Every time misfire (The same cylinder misfires every time.): FTP 1.5 times misfire, Catalyst damage misfire

The following detecting methods are adopted for these detection.
1. Intermittent misfire: FTP 1.5 times misfire
- 180° Interval Difference Method (MT: 1,800 rpm or less; AT: None)
- 360° Interval Difference Method (whole range)
- 720° Interval Difference Method (3,000 rpm or more)

2. Misfire every time: FTP 1.5 times misfire, Catalyst damage misfire
- 360° Interval Difference Method

2. ENABLE CONDITION

Enable Conditions:

Map 3

MT model









AT model






3. GENERAL DRIVING CYCLE
- If conditions are met, detect misfire from idling to high rotation.
- Perform the diagnosis continuously.

4. DIAGNOSTIC METHOD






When a misfire occurs, the engine speed will decreased and the crankshaft position speed will change. Calculate the interval difference value (diagnostic value) from crankshaft position speed by the following formula, and judge whether a misfire is occurring or not comparing the calculated result with judgment value. Counting the number of misfires, if the misfire ratio is higher during 1000 rev. or 200 rev. Judge corresponding cylinders as NG.






As shown in the given figure, pick a cylinder as the standard and name it omg 0. And the former crankshaft position speed is named omg 1, the second former crankshaft position speed is named omg 2, the third is named omg 3, etc.






180° Interval Difference Method






360° Interval Difference Method






720° Interval Difference Method






FTP 1.5 times misfire (Misfire occurrence level which influences exhaust gas)







Time Needed for Diagnosis: 1000 revs.

Malfunction Indicator Light Illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.

Catalyst damage misfire (Misfire occurrence level damaging catalyst)






Map 1 Fault criteria threshold for misfire which would result in catalyst damage






These figures indicate the misfire rate (%) in 400 ignitions; for example, 22.5 (%) means 400 (ignition) • 22.5 (%) = 90 (ignition) misfires.This value or more is judged as a misfire.

Time Needed for Diagnosis: 200 revs.

Malfunction Indicator Light Illumination: Illuminates as soon as a malfunction occurs.

5. DTC CLEAR CONDITION
- When the OK idling cycle is completed 40 times in a row
- When "Clear Memory" is performed

6. MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When a similar driving cycle is established 3 times in a row
- When "Clear Memory" is performed

7. FAIL SAFE
None

8. ECM OPERATION AT DTC SETTING
Memorize the freeze frame data. (For test mode $02)