Combustion misfire detected


P0301 - Cylinder #1

P0302 - Cylinder #2

P0303 - Cylinder #3

P0304 - Cylinder #4

P0305 - Cylinder #5

P0306 - Cylinder #6


Detection Condition

Diagnostic Support Notes

Possible Causes

Diagnostic Procedure

1.  Has FREEZE FRAME DATA been recorded?

2.  Check for related TSBs and/or online repair information.  Is any repair information available?

3.  Turn ignition key to OFF then ON (engine off).  Any other pending or current DTCs present?

4.  With an OBD interface, access engine coolant temperature (ECT), intake air temperature (IAT), mass airflow (MAF), engine revolutions per minute (RPM), throttle position (TP), and vehicle speed (VS) PIDs.  Is there any signal that is far out of specification when ignition switch is ON and engine is idling?

5.  Inspect same PIDs as in Step 4 while simulating FREEZE FRAME DATA condition. Is there any signal which causes drastic changes?

6.  Turn ignition key to OFF.  Remove spark plug from suspected cylinder and check for cracks, excessive wear, incorrect gap, or fuel saturation.  Is there a problem with the spark plug condition?

7a.  KJ Engine:  Remove coil-on-plug unit from suspected cylinder and inspect insulator for cracks or heat damage from sparks shorting to cylinder head.  Swap the COP unit with one from another cylinder to determine if the misfire DTC moves to the cylinder with the suspected COP unit.  Is COP unit okay?

7b.  KL Engine:  Remove high tension lead from suspected cylinder and inspect insulator for cracks or heat damage from sparks shorting to cylinder head.  Inspect high tension lead condition and resistance.  Inspect distributor rotor for wear or damage.  Inspect distributor cap for wear or damage.  Inspect for proper operation of the ignition coil within the distributor unit.  Are all items okay?

8.  Inspect for air leakage between the dynamic chamber and intake manifold (KJ) and between the intake manifold and cylinder head.  Is air leakage found?

9.  Remove intake-air system parts.  Disconnect fuel injector connector on suspected cylinder.  Connect noid light to fuel injector connector terminals.  Does the light indicate normal fuel injector operation while cranking?

10.  Remove radiator cap after engine has cooled sufficiently, implement system bleed procedure, then idle engine.  Are there any small bubbles, which make the engine coolant appear white at the filler opening?

11.  Inspect engine compression.  Is engine compression okay?

12.  Remove fuel injector from suspected cylinder and swap it with one from another cylinder.  Start the engine and run it at idle.  Does misfire DTC move to cylinder with suspected injector?

13.  Make sure to reconnect all disconnected connectors.  Start engine, clear DTC from ECU memory using OBD interface and perform DRIVE MODE 1.  Is a PENDING CODE for the same DTC present?

14.  Perform "After Repair Procedure" and scan for stored codes.  Is there a DTC present?



[P0301 / P0302 / P0303 / P0304 / P0305 / P0306 - From 2002 Mazda Millenia factory service manual]