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Home >> Subaru >> 2017 >> Legacy 2.5i Limited >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 14 (Engine Control System (Diagnostics) (P0161 To P0685) (H6DO)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0306 Cylinder 6 Misfire Detected >> Notes

DTC P0306 Cylinder 6 Misfire Detected: Notes

WARNING: This page is about a different variant/trim than selected.

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
G11586527Courtesy 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 and chassis ground on faulty cylinders.

Connector & terminal 
#1 (B134) No. 23 (+) - Chassis ground (-): 
#2 (B134) No. 8 (+) - Chassis ground (-): 
#3 (B134) No. 9 (+) - Chassis ground (-): 
#4 (B134) No. 22 (+) - Chassis ground (-): 
#5 (B134) No. 52 (+) - Chassis ground (-): 
#6 (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. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from fuel injector on faulty cylinders.
  3. Measure the resistance between fuel injector connector and engine ground on faulty cylinders.

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: 
#5 (E43) No. 2 - Engine ground: 
#6 (E44) 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. 
Measure the resistance of harness between ECM and fuel injector connector on faulty cylinders.
Connector & terminal 
#1 (E158) No. 23 - (E5) No. 2: 
#2 (E158) No. 8 - (E16) No. 2: 
#3 (E158) No. 9 - (E6) No. 2: 
#4 (E158) No. 22 - (E17) No. 2: 
#5 (E158) No. 52 - (E43) No. 2: 
#6 (E158) No. 13 - (E44) No. 2: 		 Is the resistance less than 1 Ω? Go to step 4.  Repair the open circuit of the harness between the ECM connector and fuel injector connector.
4 CHECK FUEL INJECTOR. 
Measure the resistance between fuel injector terminals on faulty cylinder.
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 fuel injector connector and engine ground on faulty cylinders.

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 (-): 
#5 (E43) No. 1 (+) - Engine ground (-): 
#6 (E44) 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 and fuel injector connector on faulty cylinders
  • Poor contact of coupling connector
  • Poor contact of main relay connector
  • Blown out of fuse (M/B No. 25)
6 CHECK HARNESS BETWEEN ECM AND FUEL INJECTOR. 
  1. Turn the ignition switch to OFF.
  2. Disconnect the connector from fuel injector on faulty cylinders.
  3. Turn the ignition switch to ON.
  4. Measure the voltage between ECM and chassis ground on faulty cylinders.

Connector & terminal 
#1 (E158) No. 23 (+) - Chassis ground (-): 
#2 (E158) No. 8 (+) - Chassis ground (-): 
#3 (E158) No. 9 (+) - Chassis ground (-): 
#4 (E158) No. 22 (+) - Chassis ground (-): 
#5 (E158) No. 52 (+) - Chassis ground (-): 
#6 (E158) 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 fuel injector terminals on faulty cylinder.

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 INSTALLATION , Camshaft Position Sensor.> <Ref. to INSTALLATION , Crankshaft Position Sensor.> Go to step 9. 
9 CHECK CRANKSHAFT POSITION SENSOR PLATE.  Is the crank sprocket rusted or the teeth of crankshaft position sensor plate broken? Replace the crankshaft position sensor plate. <Ref. to CYLINDER BLOCK .> Go to step 10. 
10 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 11. 
11 CHECK FUEL LEVEL.  Is the fuel meter indication lower than the "Lower" level? Refill the fuel so that the fuel meter indication is higher than the "Lower" level, and proceed to the next step. Go to step 13. 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 CYLINDER.  Is there any fault in the cylinder? Repair or replace faulty parts.
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).>
16 CHECK PCV VALVE. 
Check the PCV valve.		 Check that the PCV valve has no deformation, cracks or other damages. Repair or replace the PCV valve. Go to step 17. 
17 CHECK PCV HOSE. 
Check the PCV hose.		 Check the PCV hose assembly for cracks, damage or looseness. Repair or replace the PCV hose. Repair the poor contact of ECM connector.
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