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Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
DTC P0301, P0302, P0303, P0304 [L3] DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1 VERIFY FREEZE FRAME DATA AND DIAGNOSTIC MONITORING TEST RESULTS HAVE BEEN RECORDED 
  • Have FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS (Misfire related) been recorded?
 Yes Go to the next step.
No Record FREEZE FRAME DATA and DIAGNOSTIC MONITORING TEST RESULTS on repair order, then go to the next step.
2 VERIFY RELATED REPAIR INFORMATION AVAILABILITY 
  • Check for related Service Bulletins and/or online repair information availability.
  • Is any related repair information available?
 Yes Perform repair or diagnosis according to the available repair information.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
3 VERIFY RELATED PENDING CODE OR STORED DTCS 
  • Turn ignition switch to OFF, then ON (Engine off).
  • Verify related pending code or stored DTCs.
  • Are other DTCs present?
 Yes Go to appropriate DTC inspection. (See DTC TABLE .)
No Go to the next step.
4 VERIFY CURRENT INPUT SIGNAL STATUS (ignition switch TO ON/IDLE) 
  • Access APP1, APP2, ECT, IAT, MAF, RPM, TP_REL and VSS PIDs using the WDS or equivalent. (See PCM INSPECTION .)
  • Is there any signal that is far out of specification when ignition switch is ON and engine runs at idle?
 Yes Inspect suspected circuit and/or part according to inspection results. Then go to Step 15. (See PCM INSPECTION .)
No Go to the next step.
5 VERIFY CURRENT INPUT SIGNAL STATUS UNDER TROUBLE CONDITION 
  • Inspect same PIDs as in Step 4 while simulating FREEZE FRAME DATA condition.
  • Is there any signal which causes drastic changes?
 Yes Inspect suspected circuit and/or part according to inspection results. Then go to Step 15. (See PCM INSPECTION .)
No Go to the next step.
6 INSPECT SPARK PLUG CONDITION 
  • Turn the ignition switch off.
  • Remove spark plug from suspected cylinder.
  • Inspect spark plug condition:
    • Cracks
    • Excess wear
    • Gap
    • Wet
  • Is any problem found on spark plug?
 Yes
  • If spark plug is wet, fuel flooding is suspected. Go to step 12.
  • If spark plug has a cracks, excessive wear or improper gap, replace faulty spark plug. Then go to Step 15.
No Go to Step 8.(1)
Go to the next step.(2)
7 VERIFY HIGH-TENSION LEAD CONDITION 
  • Remove high-tension lead.
  • Inspect high-tension lead condition and resistance.
    • Cracks
    • Spark shorts to cylinder head through high-tension lead insulator
  • Is high-tension lead normal?
 Yes Go to Step 10.
No Replace high-tension lead, then go to Step 15.
8 INSPECT IGNITION COIL HARNESS 
  • Inspect the ignition coil related harness condition (intermittent open or short) for all cylinders.
  • Are harness conditions normal?
 Yes Go to the next step.
No Repair suspected wiring harnesses, then go to Step 15.
9 INSPECT IGNITION SYSTEM OPERATION 
 Yes Go to the next step.
No Repair or replace malfunctioning part according to Spark Test result. Then go to the Step 15.
10 INSPECT FOR AIR SUCTION AT INTAKE AIR SYSTEM 
  • Inspect for air leakage at following:
    • Around connection of dynamic chamber and intake manifold
    • Around connection of intake manifold and cylinder head
  • Is air leakage found?
 Yes Repair or replace suspected part, then go to Step 15.
No Go to the next step.
11 INSPECT FUEL INJECTOR HARNESS 
  • Remove intake air system parts.
  • Disconnect fuel injector connector on suspected cylinder.
  • Connect NOID LIGHT to fuel injector connector terminals.
  • Inspect light dimness during cranking.
  • Does noid light illuminate?
 Yes Go to the next step.
No Inspect fuel injector harnesses. Repair or replace it if necessary, then go to Step 15.
12 INSPECT SEALING OF ENGINE COOLANT PASSAGE 
WARNING:
  • Removing radiator cap when radiator is hot is dangerous, Scalding coolant and steam may shoot out and cause serious injury.
  • When removing radiator cap, wrap thick cloth around and turn it slowly.

  • Remove radiator cap.
  • Implement procedure to bleed air from engine coolant, then run engine at idle.
  • Is there any small bubble which makes engine coolant white at filling opening?
    NOTE:
    • Large bubbles are normal since they are remaining air coming out from engine coolant passage.
 Yes Air gets in from poor sealing on head gasket or other areas between combustion chamber and engine coolant passage. Repair or replace faulty parts, then go to Step 15.
No Go to the next step.
13 INSPECT ENGINE COMPRESSION 
 Yes Go to the next step.
No Overhaul the engine, then go to Step 15.
14 INSPECT FUEL INJECTOR OPERATION 
  • Remove fuel injector from suspected cylinder.
  • Swap injector with injector on other cylinder.
  • Start engine and run it at idle.
  • Is misfire DTC for cylinder which has a suspected fuel injector?
 Yes Replace injector, then go to the next step.
No Go to the next step.
15 VERIFY TROUBLESHOOTING OF MISFIRE DTC COMPLETED 
  • Make sure to reconnect all disconnected connectors.
  • Start engine.
  • Clear the DTC from the PCM memory using the WDS or equivalent.
  • Start engine and perform DRIVE MODE 1. (See OBD-II DRIVE MODE .)
  • Is PENDING CODE for this DTC present?
 Yes Replace PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION .)
No Go to the next step.
16 VERIFY AFTER REPAIR PROCEDURE 
 Yes Go to the applicable DTC inspection. (See DTC TABLE .)
No Troubleshooting completed.
(1) California emission regulation applicable ATX model
(2) Except for California emission regulation applicable ATX model
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