2015–2021 Subaru WRX

2015-2021 Subaru WRX — Check Engine Light / OBD2 Diagnosis

By Tom Becker ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026

🔧 Easy 15-30 minutes $25 DIY

Save $95 by doing it yourself! Shop cost: $120

Quick answer: Check Engine Light / OBD2 Diagnosis on a 2015–2021 Subaru WRX is rated Easy and takes about 15-30 minutes. You'll need 2 tools for this job, and parts cost about $25. This guide walks you through the full job step by step, including the mistakes to avoid.

Quick Video Tutorial

Parts You Need

Total Cost

$25.00

Part Name	Part Number	Price	Buy
OBD2 scanner	—	$25.00	Amazon

About prices: shown prices are typical retail averages and change frequently; cheaper alternatives may be available. Confirm the current price before buying.

💡 Pro tip: Order all parts at once to save on shipping

Step-by-Step Instructions

Follow these steps carefully

Check the lamp, then check the oil

Start the 2015-2021 Subaru WRX and read the check-engine lamp: steady means diagnose soon, flashing means an active misfire, so ease off and pull over safely. Rough running or overheating means stop, not a continued DIY scan.

Plug the scanner into the OBD port

With the ignition off, locate the 16-pin OBD-II port under the driver's-side dashboard near the steering column on the 2015-2021 Subaru WRX. Seat the scanner plug firmly, then turn the ignition to ON without starting and confirm communication and live data.

Scan codes, freeze-frame, and AVCS data

Run a full scan on the 2015-2021 Subaru WRX and record confirmed, pending, and permanent codes with freeze-frame (RPM, load, coolant temp, speed). The signature faults on the FA20DIT turbo engine are P000A/P000B/P000C/P000D camshaft slow response from the oil control valves, P0171 lean from intake leaks, P0300-series misfires, and P0457 EVAP (often the gas cap). Add live data: actual versus target AVCS cam angles, fuel trims, and boost pressure. Do not clear codes yet.

Work from oil outward to the code

For P000A-family codes on the 2015-2021 Subaru WRX, confirm the oil is full and fresh first, since these codes very often trace to oil supply at the control valves; only then suspect a sticking oil control valve, which is a professional-level replacement. For P0171, inspect the intake tract, intercooler hoses, and vacuum lines for leaks, and watch whether fuel trims are worse at idle (vacuum leak) or under load (fuel delivery). For P0457, tighten the gas cap and check the filler neck. For misfires, inspect plugs and coils.

Clear, drive, and confirm the monitors

After the verified repair on the 2015-2021 Subaru WRX, clear codes with the scanner and drive normally for several days with full warm-up cycles and mixed city and highway miles so the monitors complete. Rescan and confirm no codes return and monitors read complete.

All Done!

Test your repair before closing everything up. If something doesn't work right, double-check your steps.

⚠️ Common Mistakes to Avoid

• Replacing parts based on a code without checking wiring, connectors, or vacuum leaks
• Clearing codes before recording confirmed, pending, and permanent codes
• Using a scanner that cannot communicate with the vehicle protocol
• Treating a stored code as proof that the named sensor itself failed

Tools You'll Need

OBD-II scanner compatible with the vehicle Flashlight Notebook or phone for codes and freeze-frame data Safety glasses

Related Trouble Codes

P0300 Random/Multiple Cylinder Misfire Detected P0301 Cylinder 1 Misfire Detected P0171 System Too Lean (Bank 1) P0101 Mass Airflow Sensor Range/Performance P0174 System Too Lean (Bank 2) P0562 System Voltage Low P0302 Cylinder 2 Misfire Detected P0303 Cylinder 3 Misfire Detected

⚠️ Safety First!

• Informational DIY. EZ Car Fix is not a shop.
• A flashing check-engine light can indicate a damaging misfire; reduce load and seek professional service promptly.
• Never work under a vehicle supported only by a jack.
• Do not clear codes before recording them and the freeze-frame data.