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?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  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: Q: My car will not start or turn over.

Hello, thank you for writing in. We need to start by looking into the battery and the charging system one more time. The first thing to turn your attention to is the battery cables. You mentioned that corrosion was present...

Q: Exssesive fuel consumption

If you are suddenly having poor fuel mileage then you should also have a Check Engine Light illuminating. The light will most likely be indicating a problem with a sensor like an O2 sensor or a mass air flow sensor....

Q: One time dtc for ecm staying on when car is off.

Hello. I usually start by load testing the battery and the alternator. Both of these will cause this if they will not pass a load test. If they are fine then there are a number of circuits that can cause...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...