P1278 — Air/Fuel (A/F) Sensor 1 (Bank 1) Slow Response
CAUTIONIs it safe to drive? Drive gently and get it looked at soon — it can worsen or fail inspection.
What P1278 means
This is a manufacturer-specific code — its meaning depends on the vehicle’s make (see below).
What P1278 means on specific makes
Nissan / Infiniti CAUTION
Source: 'HO2S bank 1 - activity/slow response.' The front A/F sensor is responding too slowly, so the ECM can't trust its switching. A worn-sensor code.
- Aging/slow front A/F sensor ($100-300)
- Sensor contamination
- Exhaust leak near sensor
Check first: Compare A/F sensor response in live data; replace if sluggish. Commonly grouped with P1273/P1276.
Source: troublecodes.net/nissancodes