2009 Mazda 5 - O2 sensor manufacturer?

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2009 Mazda 5 GT - 5-speed MT
Hello all - I'm considering replacing the O2 sensor on our '09 Mazda 5. The car's running well and is not generating any "check engine" codes, but some O2 sensor manufacturers (and some independent sources) recommend replacing the upstream sensor at 100K miles/160K km. Our car is at 170K km now. There is a little bit of surging at low speed and I'm wondering whether this is an early symptom of a weak O2 sensor. (I changed the spark plugs only a few months ago, so it shouldn't be them.)

My main reason for replacing would be that by this mileage the upstream sensor will have likely become a bit 'lazy' (though not badly enough to throw a code). (I'm not sure whether this is due to the material in the sensor being depleted, or is due to the sensor being contaminated.) If it's even deteriorated enough to use 5% more fuel, that will take a toll on the catalytic convertor (besides the wasted fuel, of course). If the slight drivability issue goes away, great!

Denso and NTK appear to offer similar replacements, and ordinarily I'd be fine with either of them, but on another forum a well-respected mechanic pointed out that the 5 uses the Ford Duratec engine (a.k.a. Mazda L-series) which may use a Bosch sensor. Further, the NTK and Denso are narrowband, whereas the Bosch is a wideband sensor. If the engine is designed to use a wideband sensor, I'd rather stick with that.

I could avoid any confusion by simply buying a sensor from the dealer, but it's quite a bit more money. So, here's my multipart question:

1. Who is the OEM for the Mazda 5 O2 sensor?

2. Does anyone know whether the OEM sensor is wideband or narrowband?

3. Who has used Bosch, and are you happy with it?

4. Similarly, who has used NTK or Denso, and are you happy with it/them?

Thanks in advance!
 
1. Don't know but labeled *Japan* so eliminate Bosch.

2. [EDIT]Upstream O2 is wideband only (5 pin), downstream O2 is narrowband (4 pin) <-- except for Cali (CARB) which uses wideband for both.

3. General rule is German/Euro cars stick with Bosch, Jap stick with NTK (NGK sister line), Denso, ETC.

4. I've used Walker and NTK for this car. Go with NTK, direct replacement. I would only change due to CEL.
 
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I've replaced it with an NTK from NAPA. It's a wideband unit. Easy job - about five minutes to remove the old one and install the new one. Used a purpose-designed O2-sensor socket - 22 mm crowfoot-style. You're right, the old one (Mazda-branded) was made in Japan, so was almost certainly a Denso or NTK.

Both Denso and NTK recommend replacement @ 160K km/100K miles. The low-speed surge seems to have disappeared, and the idle feels smoother (but I may be imagining both). Glad I did it. (Our old Gen 1 MPV used to trigger a "replace O2 sensor" light on the dash every 130K km, triggered off the mechanical odometer, so I can see 160K km being reasonable.
 
SN13, right you are! I was talking about the A/F-ratio (upstream) sensor, not the cat monitor (downstream).
 
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