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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 P0300 [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 troubleshooting. (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. (See PCM INSPECTION .) Then go to Step 24.
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. (See PCM INSPECTION .) Then go to Step 24.
No Go to the next step.
6 INSPECT CMP SENSOR 
 Yes Go to the next step.
No Inspect installation condition and damage on timing chain and gears, repair faulty parts.
  • If it is normal, replace CMP sensor. Then go to Step 24.
7 VERIFY CKP SENSOR INSTALLATION CONDITION 
  • Inspect for CKP sensor looseness.
  • Is CKP sensor loose?
 Yes Retighten CKP sensor, then go to Step 24.
No Go to Step 12.(1)
Go to the next step.(2)
8 INSPECT IGNITION COIL OPERATION AND HIGH-TENSION LEAD WITH TIMING LIGHT 
  • Verify blinking condition on each cylinders using timing light at idle.
  • Do all cylinders show blinking condition?
 Yes Go to Step 14.
No Go to the next step.
9 INSPECT HIGH-TENSION LEADS OF NO BLINKING CYLINDER 
  • Turn the ignition switch off.
  • Inspect high-tension leads for improper installation, corrosion on terminal, open lead and damaged cover.
  • Is condition of high-tension lead normal?
 Yes Go to the next step.
No Replace faulty high-tension lead, then go to Step 24.
10 INSPECT POWER SUPPLY TERMINAL AT IGNITION COIL CONNECTOR 
  • Disconnect ignition coil connector.
  • Turn ignition switch to ON (Engine off).
  • Measure voltage between ignition coil terminal B (harness-side) and body ground.
  • Is voltage B+  ?
 Yes Go to the next step.
No Inspect for open circuit between ignition coil connector and ignition switch. Repair or replace wiring harness, then go to Step 24.
11 INSPECT IGNITION COIL RESISTANCE 
 Yes Go to step 24.
No Replace ignition coil, then go to Step 24.
12 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 24.
13 INSPECT IGNITION SYSTEM OPERATION 
 Yes Go to the next step.
No Repair or replace malfunctioning part according to Spark Test result.
Then go to Step 24.
14 INSPECT MAF PID 
  • Start engine.
  • Access MAF PID using the WDS or equivalent.
  • Verify that MAF PID changes quickly according to race engine RPM.
  • Is MAF PID response normal?
 Yes Go to the next step.
No Replace MAF sensor, then go to Step 24.
15 INSPECT EXCESSIVE AIR SUCTION IN INTAKE AIR SYSTEM 
  • Inspect for air leakage at following:
    • Between MAF sensor and throttle body
    • Between throttle body and intake manifold
  • Is there any malfunction?
 Yes Repair or replace suspected part, then go to Step 24.
No Go to the next step.
16 INSPECT FUEL LINE PRESSURE 
 Yes Go to Step 18.
No If fuel line pressure is too low, go to the next step. If fuel line pressure is excess high, replace fuel pump unit, then go to Step 24.
17 INSPECT FUEL LINE FROM FUEL PUMP TO FUEL DELIVERY PIPE 
  • Visually inspect for fuel leakage in fuel line for any leakage.
  • Is any fuel leakage found?
 Yes Replace suspected fuel line, then go to Step 24.
No Inspect low-pressure side fuel filter for following:
  • Foreign materials or stain inside fuel filter Perform following actions depend on the result above.
  • If foreign materials or stain is found inside fuel filter (low-pressure side), clean of fuel tank and filter (low-pressure side).
  • If normal, replace fuel pump unit.

Then, go to Step 24.
18 INSPECT ENGINE COMPRESSION 
 Yes Go to the next step.
No Implement engine overhaul for repairs, then go to Step 24.
19 INSPECT VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION 
 Yes Go to the next step.
No Repair or replace malfunctioning part according to variable valve timing control system inspection results, then go to Step 24.
20 INSPECT OPERATION OF PURGE CONTROL SOLENOID VALVE 
 Yes Go to the next step.
No Repair or replace malfunctioning part according to purge control system inspection results, then go to Step 24.
21 INSPECT PCV VALVE OPERATION 
 Yes Replace PCV valve, then go to Step 24.
No Go to the next step.
22 INSPECT OPERATION OF EGR VALVE 
  • Remove EGR valve.
  • Visually inspect for stuck to open.
  • Is EGR valve stuck to open?
 Yes Repair or replace EGR valve, then go to Step 24.
No Go to the next step.
23 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 the next step.
No Go to the next step.
24 VERIFY TROUBLESHOOTING OF MISFIRE DTC COMPLETED 
  • Make sure to reconnect all disconnected connectors.
  • Turn ignition switch to ON (Engine off).
  • Clear the DTC from the 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.
25 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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