I just purchased my car used. 2009 GT. It came with a completely aftermarket exhaust system that includes high flow cats. My check light came on and i had the dealer look at it and replaced one of my O2 sensors for 200 dollars. A few days later the light came back on and I took it in to the dealer again. Same problem. They tell me its because of the high flow cats. From my own research and from what the dealer told me i have gotten two conflicting messages. 1) the sensors are talking to my computer and making the car burn fuel differently than it would otherwise which could cause problems. 2) the sensors are for emissions monitoring ONLY and do not affect performance. My question is, will ignoring this problem damage anything? Whats the best way to fix the problem? Thanks

 

Which ones did they replace? The up stream or down stream?

 

Hey,

I'm sorry to hear about the issues you are having here, especially on a car you just purchased.

The dealership actually may be right here. Sometimes with high flow cats, the O2 sensors will still generate a code. Reason being, the high flow cats are letting more flow and a bit more pollutants out of the engine. Sometimes if your car has a particularly sensitive set of rear O2 sensors the car will still throw a code.

Letting this code go for long periods of times is certainly not advised. Whenever a check engine light comes on, the car will automatically pull timing out of the engine. This will cause your air to fuel ratios to be out of sync and will eventually cause engine build up and become very detrimental to the engine.

To correct this you will need to have some sort of tuning device. These tuners can alter the cars computer to accept a wider range or readings from the rear o2 sensors and turn off the code. I would recommend an SCT SF3.

I hope this information helps, and by all means if you have any other questions feel free to get back in touch. Best of luck!

-Dan

 

^^^^
Good advise.

 

Here is an update... I have heard of two solutions to my problem 1) get a tuner 2) used spark plug anti foulers to set the rear sensors back out of the exhaust stream. I decided for the low cost of the anti fouler trick I should do that first. This did not work. Now I am wondering if there is something else wrong here and maybe the tuner wont solve the problem? What is jumping to my mind is maybe the oxygen sensors are just bad.

 

If your car still has a stock tune and the after market cats and exhaust, you need to get the car tuned. If the last owner did not do this, your going to get codes.

 

The man from AM is exactly right:

just to put a finer point on it, cars have O2 sensors before and after the cats. the PCM uses the pre-cat sensors to monitor air:fuel ratios, and the post-cat sensors to make sure the cats are there and working. the pre-cat sensors should output an oscillating voltage as the engine regularly is run between slightly rich and slightly lean. The post-cat sensors shouldn't put out much if any oscillation, and if the signal they output starts to look too similar to the pre-cat sensors' then the PCM will flag a "catalyst efficiency" code.

 

I just put a kooks setup on and it took about a week to throw a code for the CEL. Just out of curiosity, when you had the code read, what number came up? I will be getting a tuner soon. That new Bama x4 looks sweet.