On Board Diagnosis Logic

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the crankshaft position (CKP) sensor (POS) signal to vary, ECM can determine that a misfire is occurring.

The misfire detection logic consists of the following two conditions.

1. One Trip Detection Logic (Three Way Catalyst Damage)

   On the first trip that a misfire condition occurs that can damage the three way catalyst (TWC) due to overheating, the MIL will blink.

   When a misfire condition occurs, the ECM monitors the CKP sensor (POS) signal every 200 engine revolutions for a change.

   When the misfire condition decreases to a level that will not damage the TWC, the MIL will turn off.

   If another misfire condition occurs that can damage the TWC on a second trip, the MIL will blink.

   When the misfire condition decreases to a level that will not damage the TWC, the MIL will remain on.

   If another misfire condition occurs that can damage the TWC, the MIL will begin to blink again.

2. Two Trip Detection Logic (Exhaust quality deterioration)

   For misfire conditions that will not damage the TWC (but will affect vehicle emissions), the MIL will only light when the misfire is detected on a second trip. During this condition, the ECM monitors the CKP sensor signal every 1, 000 engine revolutions.

   A misfire malfunction can be detected in any one cylinder or in multiple cylinders.

   DTC DETECTING CONDITION CHART
   
   

   DTC No.	Trouble diagnosis name	DTC detecting condition	Possible cause
   P0300 0300	Multiple cylinder misfires detected	Multiple cylinder misfire.	Improper spark plug Insufficient compression Incorrect fuel pressure The fuel injector circuit is open or shorted Fuel injector Intake air leak The ignition signal circuit is open or shorted Lack of fuel Drive plate or flywheel Air fuel ratio (A/F) sensor 1 Incorrect PCV hose connection
   P0301 0301	No. 1 cylinder misfire detected	No. 1 cylinder misfires.
   P0302 0302	No. 2 cylinder misfire detected	No. 2 cylinder misfires.
   P0303 0303	No. 3 cylinder misfire detected	No. 3 cylinder misfires.
   P0304 0304	No. 4 cylinder misfire detected	No. 4 cylinder misfires.