DTC P0300 Random/Multiple Cylinder Misfire Detected: Notes

DTC DETECTING CONDITION:

Detected when two consecutive driving cycles with fault occur.
Immediately at fault recognition (A misfire which could damage catalyst occurs.)

TROUBLE SYMPTOM:

Engine stalls.
Improper idling
Rough driving
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.>.
- Use the check board when measuring the ECM terminal voltage and resistance.

WIRING DIAGRAM:

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

Fig 1: System Too Rich Bank 1 Wiring Diagram

G11577041

Courtesy of SUBARU OF AMERICA, INC.

Step	Check	Yes	No
1 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR CONNECTOR. Turn the ignition switch to OFF. Disconnect the connector from all fuel injectors. Measure the resistance between all fuel injector connectors and engine ground. Connector & terminal #1 (E5) No. 1 - Engine ground: #1 (E5) No. 2 - Engine ground: #2 (E16) No. 1 - Engine ground: #2 (E16) No. 2 - Engine ground: #3 (E6) No. 1 - Engine ground: #3 (E6) No. 2 - Engine ground: #4 (E17) No. 1 - Engine ground: #4 (E17) No. 2 - Engine ground:	Is the resistance 1 MΩ or more?	Go to step 2 .	Repair the short circuit to ground in harness between ECM connector and fuel injector connector.
2 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 (E158) No. 12 - (E5) No. 1: #1 (E158) No. 11 - (E5) No. 2: #2 (E158) No. 24 - (E16) No. 1: #2 (E158) No. 23 - (E16) No. 2: #3 (E158) No. 36 - (E6) No. 1: #3 (E158) No. 35 - (E6) No. 2: #4 (E158) No. 48 - (E17) No. 1: #4 (E158) No. 47 - (E17) No. 2:	Is the resistance less than 1 Ω?	Go to step 3 .	Repair the open circuit of the harness between the ECM connector and fuel injector connector.
3 CHECK FUEL INJECTOR. Check all fuel injectors. <Ref. to INSPECTION , Fuel Injector.>	Is the check result OK?	Go to step 4 .	Replace the faulty fuel injector. <Ref. to FUEL INJECTOR .>
4 CHECK INSTALLATION CONDITION 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 INSTALLATION , Camshaft Position Sensor.> <Ref. to INSTALLATION , Crankshaft Position Sensor.>	Go to step 5 .
5 CHECK CRANKSHAFT POSITION SENSOR PLATE.	Is the crankshaft position sensor plate rusted or does it have broken teeth?	Replace the crankshaft position sensor plate. <Ref. to Cylinder Block .>	Go to step 6 .
6 CHECK INSTALLATION CONDITION OF TIMING CHAIN. Turn the crankshaft using ST, and align the alignment mark on crank sprocket with alignment mark on cylinder block. ST 18252AA000 CRANKSHAFT SOCKET	Is the timing chain dislocated from its proper position?	Correct the installation condition of timing chain. <Ref. to TIMING CHAIN ASSEMBLY .>	Go to step 7 .
7 CHECK FUEL LEVEL.	Is the fuel meter indication higher than the "Lower" level?	Go to step 8 .	Refill the fuel so that the fuel meter indication is higher than the "Lower" level, and proceed to the next step. Go to step 11 .
8 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 9 .
9 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 10 .
10 CHECK PCV HOSE. Check the PCV hose.	Check the clamp of PCV hose assembly for damage or looseness.	Repair or replace the PCV hose. <Ref. to PCV Hose Assembly .>	Go to step 11 .
11 CHECK STATUS OF MALFUNCTION INDICATOR LIGHT. Clear the memory using the Subaru Select Monitor or general scan tool. <Ref. to Clear Memory Mode .> Start the engine, and drive the vehicle 10 minutes or more.	Does the malfunction indicator light illuminate or blink?	Go to step 13 .	Go to step 12 .
12 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
13 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 14 .
14 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 Ignition coil Fuel injector Compression Skipping timing chain teeth	Go to DTC P0171. <Ref. to DTC P0171 SYSTEM TOO LEAN BANK 1 , Diagnostic Procedure with Diagnostic Trouble Code (DTC).>