Q: Check Engine light; upstream O2 sensor

asked by on

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
  1. Home
  2. Questions
  3. Check Engine light; upstream O2 sensor

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

Q: Replaced EGR valve and cleaned the intake but the P0401 code is still coming up after reset

Hi there. From the description you have given, your vehicle's P0401 (EGR insufficient flow) code may be a control problem. Assuming, the intake passage cleaning was successful. Good intake manifold vacuum is present at the EGR (exhaust gas recirculation) valve....

Q: Exhaust manifold overheats.

These engines and the year you have has had issues with the cooling fan switch in the radiator. The thermo switch may have an intermittent problem that lets the engine get too hot and this could cause the manifold to...

Q: Had Oxygen sensor replaced twice by different shops. Still get this code intermitently.

Hello. A technician will have to diagnose your vehicle to see exactly which wiring is at fault. There are other things which can cause an oxygen sensor check engine light such as a vacuum leak or a bad catalytic converter....

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...