[Lvazque102]

Hi there, I have a 2009 Mazda 6 3.7 v6. It has about 145,000 miles on it. Car is sounding louder normal. Could this be a bad cat or leak in the manifold. I’m attaching a picture of the O2 readings, I was told that the output should be constant and not jumping around like the first sensor.

Appreciate any help or advice. This is my first car and got her around 100,000 miles. Thank you in advanced for your time!

 

[DrFeelGood]

Hi there, I have a 2009 Mazda 6 3.7 v6. It has about 145,000 miles on it. Car is sounding louder normal. Could this be a bad cat or leak in the manifold. I’m attaching a picture of the O2 readings, I was told that the output should be constant and not jumping around like the first sensor.

Appreciate any help or advice. This is my first car and got her around 100,000 miles. Thank you in advanced for your time!

Yup... both of them are bad.
The upstream sensors (S11 and S21) which is befor the catalytic converter is used to sample the exhaust coming out of the engine. The computer uses these upstream sensors to determine you fuel mixture. The reading goes up and down between +1.0 and -1.0 and it adjusts between rich and lean fuel mixture.
The Downstream sensors (S12 and S22) are to check if the catalytic converter is doing its job. The converter burns the unburnt fuel in a catalytic reaction and should have a fairly stable signal. If the converter is bad it will not make the reaction and the reading from the downstream sensor will look like the upstream one.

Front and Rear sensors BAD | Front and Rear sensors Good

Bad cats don't tend to be loud (but can be) so you may have both problems.

 

[Lvazque102]

Wow, thank you so much. So you recommend changing both catalytic converters?

 

[DrFeelGood]

Wow, thank you so much. So you recommend changing both catalytic converters?

Its up to you really.
https://www.mazda6club.com/threads/help-me-save-mozzie-loss-of-power.410065/#post4809001
Above is my experience with a first generation v6
I ended up doing the job twice because I was not complete the first time. The pictures are all gone and I cannot update them since the forum makeover but in my case the converters dissolved and clogged the downstream cats (there are four total in my car). Since I only replaced the upstream oned the downstream ones eventually clogged and destroyed the upstream ones as well.
The recommendation for the "correct" fix is replace all the catalysts (4), oxygen sensors (4) and fix the reason why they died to begin with. In my case it is bad/old coil packs and spark plugs. Catalytic converters do not die, they are killed. Improper combustion leads to their demise.
I was planning on keeping the car for years to come and I was also doing my own work. For me to do the job I described cost me just under $1400. If I would have had it done the estimate was $4700, more than the value of the vehicle.
Keep in mind that a new car payment is around $300/mo so if you will keep it more than a year ($3600 in car payments) then it may be worth it.
That motor (3.7L) also has the water pump in the timing cover so if you haven't done that replacement yet it might be an important consideration to make before you decide. When the water pump fails it fills your oil with coolant and motors don't tend to like that.

Sorry it is not the greatest news but I would rather you go into it know more rather than less.
Good Luck.