Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Basic Diagnostic Procedure: Procedure: Engine
- CHECK ENGINE START FAILURE
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- Ask the customer when and how the trouble occurred using the interview check list. Ref. to ENGINE (DIAGNOSTICS) (STI)>Check List for Interview>CHECK .
- Start the engine.
Does the engine start?
Yes: Go to 2.
No: Inspection using "Diagnostics for Engine Starting Failure" Ref. to ENGINE (DIAGNOSTICS) (STI)>Diagnostics for Engine Starting Failure .
- CHECK ILLUMINATION OF MALFUNCTION INDICATOR LIGHT
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Does the malfunction indicator light illuminate?
Yes: Go to 3.
No: Inspection using "General Diagnostic Table". Ref. to ENGINE (DIAGNOSTICS) (STI)>General Diagnostic Table .
- CHECK COMMUNICATION STATUS
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- Turn the ignition switch to OFF.
- Connect the Subaru Select Monitor or general scan tool to the data link connector.
- Turn the ignition switch to ON, and run the Subaru Select Monitor or general scan tool.NOTE:
- Subaru Select Monitor
For detailed operation procedures, refer to the "Subaru Select Monitor". Ref. to ENGINE (DIAGNOSTICS) (STI)>Subaru Select Monitor .
- General scan tool
For detailed operation procedures, refer to the general scan tool operation manual.
- Subaru Select Monitor
Does Subaru Select Monitor or general scan tool communicate with vehicle normally?
Yes: Go to 4.
No: Inspection using "Diagnostic Procedure for Subaru Select Monitor Communication". Ref. to ENGINE (DIAGNOSTICS) (STI)>Diagnostic Procedure for Subaru Select Monitor Communication .
- CHECK DTC
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Read DTC using Subaru Select Monitor or general scan tool.
NOTE:- Subaru Select Monitor
For detailed operation procedures, refer to "Read Diagnostic Trouble Code (DTC)". Ref. to ENGINE (DIAGNOSTICS) (STI)>Read Diagnostic Trouble Code (DTC) .
- General scan tool
For detailed operation procedures, refer to the general scan tool operation manual.
Is DTC displayed on Subaru Select Monitor or general scan tool?
Yes: Record DTC and freeze frame data, then repair the trouble cause. Ref. to ENGINE (DIAGNOSTICS) (STI)>List of Diagnostic Trouble Code (DTC) . after repair, go to the next step. GO to 5.
NO: Repair the related parts.
NOTE: If DTC is not shown on display although the malfunction indicator light illuminates, perform the diagnosis of malfunction indicator light circuit or combination meter. Ref. to ENGINE (DIAGNOSTICS) (STI)>Malfunction Indicator Light . - Subaru Select Monitor
- PERFORM DIAGNOSIS
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- Perform the Clear Memory Mode. Ref. to ENGINE (DIAGNOSTICS) (STI)>Clear Memory Mode .
- Perform the Inspection Mode or Drive Cycle. Ref. to ENGINE (DIAGNOSTICS) (STI)>Inspection Mode . Ref. to ENGINE (DIAGNOSTICS) (STI)>Drive Cycle .
Is DTC displayed on Subaru Select Monitor or general scan tool?
Yes: Inspect using "Diagnostic Procedure with Diagnostic Trouble Code (DTC)". Ref. to WRX STI (2.5L) .
No: Finish the diagnosis.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.