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DTC P0300 Random/Multiple Cylinder Misfire Detected: Notes

DTC DETECTING CONDITION: 

TROUBLE SYMPTOM: 

CAUTION: After servicing or replacing faulty parts, perform Clear Memory Mode <Ref. to OPERATION , Clear Memory Mode.>, and Inspection Mode <Ref. to PROCEDURE , Inspection Mode.>.

WIRING DIAGRAM: 

Engine Electrical System <Ref. to WIRING DIAGRAM , Engine Electrical System.>

Fig 1: Cylinder 1 Injector A Circuit Wiring Diagram
G11574204Courtesy of SUBARU OF AMERICA, INC.
Step Check Yes No
1 CHECK OUTPUT SIGNAL OF ECM. 
  1. Turn the ignition switch to ON.
  2. Measure the voltage between ECM connector and chassis ground on all cylinders.

    Connector & terminal 

    #1 (B134) No. 10 (+) - Chassis ground (-): 

    #2 (B134) No. 11 (+) - Chassis ground (-): 

    #3 (B134) No. 12 (+) - Chassis ground (-): 

    #4 (B134) No. 13 (+) - Chassis ground (-): 

 Is the voltage 10 V or more? Go to step 6  . Go to step 2  .
2 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from all fuel injectors.
  3. Measure the resistance between all fuel injector connectors and engine ground.

    Connector & terminal 

    #1 (E5) No. 2 - Engine ground: 

    #2 (E16) No. 2 - Engine ground: 

    #3 (E6) No. 2 - Engine ground: 

    #4 (E17) No. 2 - Engine ground: 

 Is the resistance 1 MΩ or more? Go to step 3.  Repair the short circuit to ground in harness between ECM connector and fuel injector connector.
3 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR. 
Measure the resistance of harness between ECM connector and fuel injector connector on all cylinders.
Connector & terminal 
#1 (B134) No. 10 - (E5) No. 2: 
#2 (B134) No. 11 - (E16) No. 2: 
#3 (B134) No. 12 - (E6) No. 2: 
#4 (B134) No. 13 - (E17) No. 2: 		 Is the resistance less than 1 Ω? Go to step 4.  Repair the harness and connector.
NOTE: In this case, repair the following item:
  • Open circuit in harness between ECM connector and fuel injector connector
  • Poor contact of coupling connector
4 CHECK FUEL INJECTOR. 
Measure the resistance between all fuel injector terminals.
Terminals 
No. 1 - No. 2: 		 Is the resistance 5 - 20 Ω? Go to step 5.  Replace the faulty fuel injector. <Ref. to Fuel Injector .>
5 CHECK POWER SUPPLY LINE. 
  1. Turn the ignition switch to ON.
  2. Measure the voltage between all fuel injector connectors and the engine ground.

    Connector & terminal 

    #1 (E5) No. 1 (+) - Engine ground (-): 

    #2 (E16) No. 1 (+) - Engine ground (-): 

    #3 (E6) No. 1 (+) - Engine ground (-): 

    #4 (E17) No. 1 (+) - Engine ground (-): 

 Is the voltage 10 V or more? Repair the poor contact of all connectors in fuel injector circuit. Repair the harness and connector.
NOTE: In this case, repair the following item:
  • Open circuit in harness between the main relay connector and fuel injector connector on faulty cylinders
  • Poor contact of coupling connector
  • Poor contact of main relay connector
6 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from all fuel injectors.
  3. Turn the ignition switch to ON.
  4. Measure the voltage between ECM connector and chassis ground on all cylinders.

    Connector & terminal 

    #1 (B134) No. 10 (+) - Chassis ground (-): 

    #2 (B134) No. 11 (+) - Chassis ground (-): 

    #3 (B134) No. 12 (+) - Chassis ground (-): 

    #4 (B134) No. 13 (+) - Chassis ground (-): 

 Is the voltage 10 V or more? Repair the short circuit to power in harness between ECM connector and fuel injector connectors. Go to step 7  .
7 CHECK FUEL INJECTOR. 
  1. Turn the ignition switch to OFF.
  2. Measure the resistance between all fuel injector terminals.

    Terminals 

    No. 1 - No. 2: 

 Is the resistance 5 - 20 Ω? Go to step 8.  Replace the faulty fuel injector. <Ref. to Fuel Injector .>
8 CHECK INSTALLATION OF CAMSHAFT POSITION SENSOR/CRANKSHAFT POSITION SENSOR.  Is the camshaft position sensor or crankshaft position sensor loosely installed? Tighten the camshaft position sensor or crankshaft position sensor. <Ref. to Camshaft Position Sensor .> <Ref. to Crankshaft Position Sensor .> Go to step 9. 
9 CHECK CRANK SPROCKET  .
Remove the timing belt cover.		 Is the crank sprocket rusted or does it have broken teeth? Replace the crank sprocket. <Ref. to Crank Sprocket .> Go to step 10. 
10 CHECK INSTALLATION CONDITION OF TIMING BELT. 
Turn the crankshaft, and align alignment mark on crank sprocket with alignment mark on cylinder block.
ST 499987500 CRANKSHAFT SOCKET		 Is the timing belt dislocated from its proper position? Repair the installation condition of timing belt. <Ref. to Timing Belt .> Go to step 11. 
11 CHECK FUEL LEVEL.  Is the fuel meter indication higher than the "Lower" level? Go to step 12.  Refill the fuel so that the fuel meter indication is higher than the "Lower" level, and proceed to the next step. Go to step 12. 
12 CHECK STATUS OF MALFUNCTION INDICATOR LIGHT. 
  1. Clear the memory using the Subaru Select Monitor or general scan tool. <Ref. to Clear Memory Mode .>
  2. Start the engine, and drive the vehicle 10 minutes or more.
 Does the malfunction indicator light illuminate or blink? Go to step 14.  Go to step 13 
13 CHECK CAUSE OF MISFIRE.  Was the cause of misfire identified when the engine is running? Finish diagnostics operation, if the engine has no abnormality. Repair the poor contact of connector.
NOTE: In this case, repair the following item:
  • Poor contact of ignition coil connector
  • Poor contact of fuel injector connector on faulty cylinders
  • Poor contact of ECM connector
  • Poor contact of coupling connector
14 CHECK AIR INTAKE SYSTEM.  Is there any fault in air intake system? Repair the air intake system.
NOTE: Check the following items.
  • Are there air leaks or air suction caused by loose or dislocated nuts and bolts?
  • Are there cracks or any disconnection of hoses?
 Go to step 15. 
15 CHECK PCV VALVE. 
Check the PCV valve.		 Is the PCV valve free from deformation, crack or other damage? Repair or replace the PCV valve. <Ref. to PCV Valve .> Go to step 16. 
16 CHECK PCV HOSE. 
Check the PCV hose.		 Is the PCV hose free from deformation, crack or other damage? Check the PCV hose assembly for cracks, damage or looseness. <Ref. to PCV Hose Assembly .> Go to step 17. 
17 CHECK PCV HOSE. 
Check the PCV hose.		 Check the clamp of PCV hose assembly for damage or looseness. Repair or replace the PCV valve. <Ref. to PCV Hose Assembly .> Go to step 18. 
18 CHECK ALL CYLINDERS.  Is there a fault in any cylinder? Repair or replace the faulty part of the faulty cylinder.
NOTE: Check the following items.
  • Spark plug
  • Fuel injector
  • Ignition coil
  • Compression
  • Skipping timing belt teeth
 Go to DTC P0171. <Ref. to DTC P0171 SYSTEM TOO LEAN BANK 1 , Diagnostic Procedure with Diagnostic Trouble Code (DTC).>
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