P0303
DTC PO301CYLINDER 1 MISFIRE DETECTED (MIS-1)
DTC PO3O2
CYLINDER 2 MISFIRE DETECTED (MIS-2)
DTC PO303
CYLINDER 3 MISFIRE DETECTED (MIS-3)
DTC PO3O4
CYLINDER 4 MISFIRE DETECTED (MIS-4)
DTC Detecting Condition
- Two consecutive trips with fault.
- Immediately at fault recognition (A misfire which could damage the catalyst occurs.)
Trouble Symptom
- Engine stalls.
- Erroneous idling.
- Rough driving.
1. Connect Subaru Select Monitor and read data.
a. Turn ignition switch to "OFF".
b. Connect Subaru Select Monitor to the Data Link Connector.
c. Turn Ignition switch to "ON" and turn Subaru Select Monitor switch to "ON".
d. Read data on Subaru Select Monitor.
Designate mode use function key.
Function mode: F33, F34, F35, F36, F37 and F38
NOTE: F37 and F38 are A/T models only.
- F33: Maximum misfire rate of Cylinder #1 is indicated.
- F34: Maximum misfire rate of Cylinder #2 is indicated.
- F35: Maximum misfire rate of Cylinder #3 is indicated.
- F36: Maximum misfire rate of Cylinder #4 is indicated.
- F37: Maximum EGR system pressure value is indicated.
- F38: Minimum EGR system pressure value is indicated.
e. Clear memory on Subaru Select Monitor.
- Designate mode use function key.
- Press [F], [C], [0], [ENT] in that order.
f. Start engine and drive the vehicle more than 10 minutes.
g. Read data on Subaru Select Monitor.
- Designate mode use function key.
- Function mode: F33, F34, F35 and F36.
[CHECK]: Is the maximum misfire rate of each cylinder less than 2%?
[YES]: :Go to next [CHECK].
[NO]: Go to step 3.
[CHECK]: The vehicle has been empty of fuel.
[YES]: The engine has no abnormality.
Finish diagnostics operation.
[NO]: Go to next [CHECK].
[CHECK]: Check if the cause of misfire was made when the engine is running. Ex. Remove spark plug cord, etc.
[YES]: The engine has no abnormality.
Finish diagnostics operation.
[NO]: Repair poor contact in ignitor, ignition coil, fuel injector, ECM, and coupling harness connector.
3. Check air intake system.
[CHECK]: 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?
[YES]: Repair air intake system.
[NO]: Go to step 4.
4. Check misfire symptom.
NOTE: Perform diagnosis according to the items listed below. Use the MAX. misfire rate values read in steps # b - d).
DTC MAX. MISFIRE RATE NEXT [CHECK]
Only 1 Cylinder ----- Go to # a.
P0301 & P0302 Both at 100% or more Go to # b.
P0303 & P0304 Both at 100% or more Go to # c.
P0301 & P0303 Both at 100% or more Go to # d.
P0302 & Po304 Both at 100% or more Go to # e.
Others ----- Go to # f.
a. Only one cylinder.
[CHECK]: Check the following items for that cylinder.
- Spark plug.
- Spark plug cord.
- Fuel injector.
- Compression ratio.
b. Group of #1 and #2 cylinders.
[CHECK]: Check the following items for #1 and #2 cylinders.
- Spark plugs.
- Fuel injectors.
NOTE: It no abnormality is discovered, check fuel injector circuit of the #1 and #2 cylinders side.
c. Group of #3 and #4 cylinders.
[CHECK]: Check the following items for #3 and #4 cylinders.
- Spark plugs.
- Fuel injectors.
NOTE: If no abnormality is discovered, check fuel injector circuit of the #3 and #4 cylinders side.
d. Group of #1 and #3 cylinders.
[CHECK]: Check the following items for #1 and #3 cylinders.
- Spark plugs.
- Fuel injectors.
- Skipping timing belt teeth.
e. Group of #2 and #4 cylinders.
[CHECK]: Check the following items for #2 and #4 cylinders.
- Spark plugs.
- Fuel injectors.
- Skipping timing belt teeth.
f. The cylinder at random.
[CHECK]: Is the Engine idle rough?
[YES]: Go to next [CHECK]. (A/T models only).
[NO]: Go to DTC P0170.
NOTE: On M/T models go to DTC PO170.
[CHECK]: Is the differential pressure between maximum Exhaust Gas Recirculation (EGR) System pressure (value of function mode F37) and minimum EGR system pressure (value of function mode F38) less than 10 mmHg?
NOTE: Use the values in step 3 for function modes F37 and F38.
[YES]: Replace EGR valve.
[NO]: Go to DTC PO170.