I am getting my oxygen sensor replaced today and the mechanic gave the car back so I could do errands while the part is being delivered, which will take several hours. In the meantime, the car's oxygen sensor has been removed.

I notice that the car engine is a lot more noisy and when I accelerate, it sounds like a chainsaw.

Is this just because the oxygen sensor has been removed so there is hole in the cat emitting noise, or is the engine making a fundamentally different noise due to different running behavior?

What effect on the mixture or other engine management parameters will driving without the oxygen sensor cause?

Note that this was the post-cat sensor.

  • It makes sense that the mechanic removed the old sensor to check he really was ordering the exact same replacement part, but IMO not spending literally 30 seconds replacing it, and leaving you driving around with a hole in your exhaust system was a bit cheapskate!
    – alephzero
    Jan 17, 2017 at 0:06

3 Answers 3


Which sensor was removed? Pre- or post-cat? If pre-cat, it could be causing the engine to run differently. If post-cat, it's just noise and your engine shouldn't be running any differently ... it just sounds that way. For most cars (and I'd bet your Volvo is one of them), the after cat O2 sensor does nothing for the running of the engine, it just checks for the function of the cat in regards to OBDII diagnostics. The pre-cat O2 sensor does affect how the engine runs, though it would just be thrown into open-loop on a continual basis, which means more fuel being dumped and of course the noise from exhaust escaping from the exhaust at the O2 bung. It shouldn't be that much of a difference, though, in how it runs overall.


The oxygen sensor is used in a feedback loop with 2 integrators (long term and short term). Essentially it determines how much oxygen is left during the combustion cycle to figure out how much to put on the next cycle. The short term integrator is doing this continuously and adjusts for things like engine and air temperature, etc; the long term integrator is adjusting for how the engine runs over its lifespan and for different geographical areas, seasons, gas type, etc.

To answer your question: the car will run fine; it will use conservative values that will run a bit rich (too much fuel compared to the air) but this will not have any adverse effect on the engine health, etc. You'll just lose a bit of power, use an unnoticeable amount of extra gas and pollute a tiny bit more during that time, but it'll be fine.


You'll just lose a bit of power, use an unnoticeable amount of extra gas and pollute a tiny bit more during that time!... What's that a whole lot of problem my man!!!

  • Welcome to Motor Vehicle Maintenance & Repair! Please realize, he did post this as the "post cat" O2 sensor. This is a '96 Volvo, so early stages of OBDII. Not going to affect how it runs or how much gas it uses. Nothing but a little extra noise. Gunna pretty much be a non-event. Oct 9, 2018 at 13:05

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .