O2 Sensor Exhaust Sample Error (Bank 1 Sensor 1)

Possible causes

• CommonExhaust leak upstream of the sensor, drawing fresh air into the stream
• CommonSensor not seated or sealed properly in its boss
• CommonCracked exhaust manifold, which can seal as it expands and leak when cold
• CommonFailed sensor
• PossibleCrushed or damaged sensor tip after an impact or careless fitting
• PossibleSoot or silicone contamination coating the sensing element

What you might notice

• Rough running or hesitation
• Poor fuel economy
• Ticking or blowing from the exhaust, loudest when cold
• Fuel trims running well positive on the affected bank
• Check engine light on

What to check, in order

1. Listen for an exhaust leak with the engine cold, before the joints expand and seal themselves. A leak that is obvious at cold idle can be silent once warm, which is why this check has to be done first thing rather than after the car has been driven in.
2. Check the fuel trims. A large positive trim on the affected bank alongside this code is the signature of an air leak rather than a genuinely lean engine.
3. Inspect the sensor's seat and threads. One that was cross-threaded or left under-tightened leaks around itself and produces exactly this.
4. Compare the two banks on a V engine. One bank behaving and the other not points at that bank's exhaust rather than at anything the engine is doing as a whole.
5. Replace the sensor last. This code is about what reaches the sensor, so a new sensor in the same leaking exhaust will report the same thing.