Q: Check Engine light; upstream O2 sensor

asked by on February 08, 2016

The Check Engine light is on again, and the code says it's the upstream O2 sensor.

Hi there. If you have a code for the upstream O2 sensor then that is the most likely problem. Knowing the code would help me to be able to tell for sure what is going on. If you replaced the sensor and the same code returned then you may have used the wrong type/brand of sensor, or there may be a problem with the fuel mixture. A vacuum leak or leaking fuel injector can cause an O2 sensor code. If the sensor is new then a mechanic would typically install a computer scan tool in order to check the fuel mixture to see what is going on.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

How do I deactivate the security alarm?

The security system alarm will activate when someone opens the vehicle without having a key or a remote transmitter. When the security system is activated, the horn will honk and the lights will flash. To deactivate the system, use a...

Is it bad to floor the gas pedal on your car?

Occasional severe acceleration is substantially harmless to an otherwise normally functioning engine. The issue of accelerated wear typical arises if the severe use is consistent and continuing over a period of time. Rates of acceleration, high or low, have absolutely...

Stabilizer link loose light coming on

Hello. Thank you for writing in. The stabilizer link and traction control lights can illuminate for several reasons. The simple fix would be if a sensor has failed somehow. The more complex issues would include mechanical damage or failure of...

Related articles

P2257 OBD-II Trouble Code: Secondary Air Injection System Control A Circuit Low
P2257 P2257 code definition Secondary Air Injection System Control A Circuit Low What the P2257 code means P2257 is an OBD-II generic code. The Engine Control Module (ECM) monitors the secondary air injection system control valve A circuit, when the...
P0468 OBD-II Trouble Code: EVAP Control System Malfunction
P0468 P0468 code definition The P0468 code is defined as Purge Flow Sensor Circuit High Input. Co-existing OBD-II codes may include P0440 or P0442, often indicating a loose gas cap, or P0443 through P0449, which can indicate an EVAP Purge...
P0111 OBD-II Trouble Code: IAT sensor circuit range or performance problem
P0111 P0111 code definition Intake Air Temperature (IAT) sensor circuit range or performance problem What the P0111 code means P0111 is the OBD-II generic code that indicates the engine control module (ECM) has recorded the IAT sensor input go out...