Subaru OBD Codes
boxer engine faults explained
The codes Subaru owners actually see — AVCS cam timing, misfires, catalysts and O2 sensors — with clear causes and fixes.
Subaru check engine light codes
Subaru uses standard OBD-II engine codes. Its boxer engines use AVCS (active valve control system), which produces distinctive cam-timing codes like P0011 and P0021.
Here are the codes most reported on Outback, Forester, Impreza, WRX and Crosstrek models.
OBD-II code decoder
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Most common Subaru
Classic Subaru faults behind these codes.
| Code | Description |
|---|---|
| P0011 | "A" Camshaft Position Timing Over-Advanced (Bank 1) |
| P0021 | "A" Camshaft Position Timing Over-Advanced (Bank 2) |
| P0133 | O2 Sensor Slow Response (Bank 1, Sensor 1) |
| P0171 | System Too Lean (Bank 1) |
| P0300 | Random/Multiple Cylinder Misfire |
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) |
| P0442 | EVAP System Small Leak Detected |
| P0507 | Idle Control System RPM Higher Than Expected |
Common Subaru faults
Classic Subaru faults behind these codes.
AVCS timing (P0011/P0021) — oil pressure or oil control valve issues on boxer engines.
Misfires (P0300) — coils, plugs, or head-gasket-adjacent coolant issues on older engines.
Catalyst efficiency (P0420) — aging converter, common on higher-mileage models.
O2 sensor slow (P0133) — upstream sensor wear.
EVAP leaks (P0442) — fuel cap or hoses.
Subaru FAQ
What causes P0011/P0021 on a Subaru?
Why does my Subaru misfire?
Is P0420 common on Subaru?
Can I read Subaru codes with a generic scanner?
Are the codes different on WRX vs Outback?
Codes vary slightly by model, year and engine. Always confirm with a proper diagnosis. Manufacturer-specific codes (P1xxx/P2xxx) may differ from generic descriptions.
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