2014 Subaru P0420: What It Means & Is It Safe to Drive?
P0420 on the 2014 Subaru: Catalyst System Efficiency Below Threshold (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
What this code means
The downstream oxygen sensor detects that the catalytic converter is not storing or converting exhaust properly. This is one of the most common check engine codes.
Common causes on the 2014 Subaru
- Failed or aging catalytic converter
- Faulty downstream oxygen sensor
- Exhaust leak before or after the catalyst
- Engine misfire or rich/lean condition damaging the catalyst
Symptoms
- Check Engine Light on
- Often no drivability issues
- Possible failed emissions test
- Rotten egg smell in some cases
Typical fixes
- Replace catalytic converter
- Replace oxygen sensor(s)
- Repair exhaust leaks
- Fix underlying fuel/ignition issues first
Repair cost range
For a 2014 Subaru, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Subaru
Subaru P0420 on the EJ25 2.5L engine is almost always connected to the infamous head gasket failure. Coolant entering the combustion chamber poisons the catalyst rapidly—if you see P0420 alongside white exhaust smoke or coolant loss, do a head gasket diagnosis before spending money on a catalyst. The cat itself is often collateral damage. On turbocharged WRX/STI EJ257 engines, oil consumption via turbo seals also destroys cats; replace the turbo seal before the converter.
Most commonly affected models