Skip the auto shop - Our mechanics make house calls

Q: O2 sensor or converter, ECM, or harness?

asked by on

Two O2 sensors are bad in the codes also saying low flow. The engine has a very rough idle once started to the point of stalling. Once it's moving it really runs quite well with almost no noticeable problem. Only at idol us it noticeable and very noticeable it is.

My car has 159000 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 information, the ECU then makes fuel adjustments to the engine. 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. To little oxygen may be present 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. I would suggest having an expert from YourMechanic come to your home to diagnose your emissions system.

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

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: Fuel gauge not reading correctly

Code P0463 is a code for fuel level Circuit A having an issue. The most likely candidate is a faulty fuel level sensor in the gas tank. The sensor has a float on the end of an arm that connects...

Q: Check engine light

Hi There, The [oxygen sensors]((https://www.yourmechanic.com/services/oxygen-sensor-replacement) 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...

Q: P0171 bank 1 upstream O2 sensor

Hello, thank you for writing in. The bank 1 upstream oxygen sensor is referring to the oxygen sensor that is before the catalytic converter. If looking at the exhaust system, it would be located on the main pipe between the...

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...
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...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.