Mazda 6 O2 sensor - CA emission

[Chester11]

Taking a flyer here as the mazda forums are dead. I have an 07 Mazda 6 with a 4 cyl 2.3 liter.

It appears to have 2 upstream O2 sensors and 1 downstream. Some online folks confirm this is true for a CA emission system.

However, the shop manual only says there are PIDs for 2. This is confirmed by my scan tool.

Voltage data is all over the place - it is possible that 2 sensors report on one PID? Or is my scan tool not seeing all 3 for some reason?

 

[zzyzzx]

How many miles are on this vehicle?

Personally, I wouldn't trust an O2 sensor with more then 100K miles on it. Also, I change them all at once. Never had any issues doing this either.

 

[supton]

I wouldn't think it'd be one PID for all or more than one. Ultimately the dealer has to be able to read each one.

Voltage all over the place--I'd expect the upstream to be all over the place, swinging high and low. I'd expect the downstream to be the one more or less solid.

 

[JMJNet]

What is the symptoms? Do you have DTCs?

 

[Chester11]

91K. No codes. Just a shake at idle in gear when hot. I was thinking vacuum leak, but the short term trim is about 0 at idle. Others have said motor mount, which could be correct, but I am smelling some exhaust under the hood. (I also just had a seized caliper, which was the cause of much of the burning smell).

The only thing that seemed odd was that the upstream doesn't appear to cycle - but since I don't know which one I'm looking it, it's not much of finding.

The shop manual isn't much help - the decision tree ends in replace cat. Thanks!

Really just trying to run down what I can before taking it in.

 

[bdcardinal]

There is only 1 air/fuel sensor. The other 2 are cat monitor O2 sensors.

 

[supton]

Is there emission testing in PA? I'd be tempted to ignore it.

FWIW, last summer I got curious and plugged in Torq to just see if I might have some lazy O2 sensors on my car, as it just seems like low mpg. Only to find out that my rear (downstream) O2 sensor was reading 0V. Always. I put one on order, put a couple hundred miles onto the car over next couple of days. No engine light. ?! Put in new sensor, same mpg, no change to the car. Was shocked that there was no code thrown for the dead O2.

 

[bdcardinal]

Originally Posted By: supton
Is there emission testing in PA? I'd be tempted to ignore it.

FWIW, last summer I got curious and plugged in Torq to just see if I might have some lazy O2 sensors on my car, as it just seems like low mpg. Only to find out that my rear (downstream) O2 sensor was reading 0V. Always. I put one on order, put a couple hundred miles onto the car over next couple of days. No engine light. ?! Put in new sensor, same mpg, no change to the car. Was shocked that there was no code thrown for the dead O2.


A rear O2 will not affect mpg because it is only there to monitor catalyst efficiency.

 

[supton]

Originally Posted By: bdcardinal
Originally Posted By: supton
Is there emission testing in PA? I'd be tempted to ignore it.

FWIW, last summer I got curious and plugged in Torq to just see if I might have some lazy O2 sensors on my car, as it just seems like low mpg. Only to find out that my rear (downstream) O2 sensor was reading 0V. Always. I put one on order, put a couple hundred miles onto the car over next couple of days. No engine light. ?! Put in new sensor, same mpg, no change to the car. Was shocked that there was no code thrown for the dead O2.


A rear O2 will not affect mpg because it is only there to monitor catalyst efficiency.


I know it's for that, primarily, but I thought some makers could use it to calibrate the upstream. Use wideband up front, narrowband out back. Thus if the downstream got out of wack, it could upset things. I forget where I came across the idea, and a quick look doesn't find it, so it could be the mis-memories of youth.

 

[UG_Passat]

Originally Posted By: supton
Is there emission testing in PA? I'd be tempted to ignore it.

FWIW, last summer I got curious and plugged in Torq to just see if I might have some lazy O2 sensors on my car, as it just seems like low mpg. Only to find out that my rear (downstream) O2 sensor was reading 0V. Always. I put one on order, put a couple hundred miles onto the car over next couple of days. No engine light. ?! Put in new sensor, same mpg, no change to the car. Was shocked that there was no code thrown for the dead O2.


Certain parts of PA has emissions testing, usually centered around Pittsburgh and Philadelphia

 

[Chester11]

No testing around me - but I'm sure it's a fail if it throws a code. I'm more concerned about the drivability.

So am I understanding - 1 Air/Fuel Sensor, and 2 O2s?

Anyone happen to know what PID I should be looking at for Air/Fuel? Shop manual is no help, and the parts stores use the terms interchangeably.

 

[Chester11]

I found it - S1 is air/fuel measured in mA. S2 and S3 are the O2 sensors.

So apparently there is a TSB for these on the Mazda. I need to look into it further.