2015 Subaru P0172: What It Means & Is It Safe to Drive?
P0172 on the 2015 Subaru: System Too Rich (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
PowertrainMedium urgency
What this code means
Too much fuel relative to air. O2 sensor detects low oxygen in exhaust; PCM is reducing fuel trim.
Common causes on the 2015 Subaru
- Faulty MAF or O2 sensor
- Leaking fuel injector(s)
- High fuel pressure
- Faulty purge valve stuck open
Symptoms
- Check Engine Light
- Rich smell, black smoke
- Poor fuel economy
- Rough idle possible
Typical fixes
- Replace MAF or O2 sensor
- Test fuel pressure and injectors
- Replace purge valve if stuck open
Repair cost range
For a 2015 Subaru, repairs for P0172 typically fall between $100 and $600, depending on the root cause and labor rates in your area.
Known issues on Subaru
P0172 on Subaru can result from coolant entering the combustion chamber through a failing head gasket, causing the ECM to see a rich condition from partial misfiring. Always verify head gasket integrity on EJ engines.
Most commonly affected models
Outback 2005–2012Forester 2004–2013Impreza 2004–2014