Skip the auto shop - Our mechanics make house calls

Q: O2 Sensors

asked by on

I am getting a check engine light. Took to dealer and they said all four O2 sensors came up on diagnostic. They said unlikely that all fail at once reset and told me to drive it. Chk eng light came back on a mile down the road. What should I check?

My car has 170000 miles.
My car has an automatic transmission.

As you may know the oxygen sensors, which are part of your emissions system, read exhaust gases to determine whether or not the appropriate amount of oxygen is present in the exhaust. Based upon this reading, this information is relayed to the car’s engine control unit (ECU), which then makes a determination as to whether or not to add more or less fuel to the engine. When too much or too little oxygen is present, this will cause check engine light to come on. Too much oxygen may be present in the exhaust gas due to things like an exhaust leak, a vacuum leak, a faulty mass air flow sensor (causing a lean fuel condition) or faulty fuel injectors. Too little oxygen in the exhaust gas may be caused by things like a clogged air filter, a failing mass air flow sensor (causing too much fuel to be introduced to the motor), bad fuel injectors or a clogged catalytic converter. When the O2 sensor is not working properly, this will cause false readings to be relayed to the computer causing inaccurate adjustments to be made to the intake and fuel system in your engine. If you want assistance in diagnosing what is the cause of this symptom, a certified YourMechanic technician can come to your location to perform a Check Engine Light is on Inspection on your vehicle and suggest any repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 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!

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: One month ago cel came on I changed spark plugs to after market plugs. One month later cel on again with misfire code.

If the spark plugs hadn't been changed until 130k, it was time for the to be replaced anyway. This is probably why the dealer went with that repair as worn spark plugs can cause misfires. Ignition coils are another part...

Q: A/C blowing out of defrost and vents

The mode door has an actuator that may not be moving the mode door when you are changing position where you want the air to blow. You will need to have the mode door actuator wiring checked and verified it...

Q: My engine light turns on, and i went to autozone to diagnosis, and it's faulty o2 sensor. Would you be able to replace it?

If code P0136 sets the only way you can determine if the oxygen sensor has failed is to use an automotive scope to graphically depict the sensor output waveform (it will look roughly like a sine wave) and switching rate...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...