I was looking at oxygen sensors for my vehicle on rock auto and found large price discrepancies. I saw sensors ranging from $25 up to $100. in general what do the more expensive sensors have that the cheaper ones don't?
In a word? Nothing. I mean, a 4-wire O2 is going to be about the same no matter what it's made for. The connector may be different, but the guts are going to be pretty much the same.
Unfortunately, you really need to know what works well with your vehicle. For instance, Bosch (from my understanding) originated the O2 sensor. Their product should be above reproach. They work well in most vehicles. For some reason they didn't work well in my 94 Camaro. This was a known thing amongst Camaro owners; it wasn't just internet hearsay. There are too many firsthand accounts of them going bad in our cars. The regular option were either ACDelco, Delphi, NTK, or (my favorite) Denso. These would last for a length of time you'd expect.
Point is, don't be afraid of the cheaper sensors. Ones like Denso are much cheaper than Bosch, but should provide you with the same service life. I don't think I would trust ones which you don't recognize the name. These are probably Chinese knockoffs. While the Chinese could be making decent O2's, their product quality/manufacturing practices have shown need for improvement. This is my opinion, though.
In general what do the more expensive sensors have that the cheaper ones don't?
There is no functional difference; all 4-wire zirconia-based narrowbands should exhibit the following:
- useful voltage range 0.1 - 0.9 V
- stoichiometric AFR at 0.45 V
- low voltage = lean condition, high voltage = rich condition
Certain brands may have a quicker warm-up time or response time to AFR changes compared to others, but the above-mentioned behavior will not change.
I imagine the difference in price will be due to a few key factors:
Different supply chains
In my experience this has a huge impact on the final price that you pay. Don't assume that Brand A and Brand B are comparable because you're buying them from the same online retailer.
Sometimes you pay for the name rather than the sensor. It's quite common to have the same sensor sold under different brand names (I've seen this with AC Delco and Denso).
I imagine that manufacturing tolerances and material quality can impact the response time and useful life of an O2 sensor. A better build will command higher costs that influences prices.
All 4-wire sensors should functionally be the same, but the location of the sensor will influence factors like operating temperature. A pre-cat O2 sensor located in the exhaust manifold will experience higher temperatures compared to one that is located in front of the catalytic converter. The design specifications for these two locations could drive differences in the materials and manufacturing process that are employed, and might explain why certain cars don't like certain sensors.
The other answers have covered most things, but here are two points that haven't yet been mentioned.
This is usually a function of the supplier rather than the manufacturer, but some places offer a lifetime guarantee. Others offer none.
How hard could it possibly be to make accurate threads? Apparently pretty hard for some manufacturers who are not quite up to 21st century manufacturing techniques and quality control.
At Rockauto, an upstream Denso O2 sensor for my Toyota Tacoma costs $107 with no warranty, while the same sensor from Bosch has at least a 12 month or more warranty and costs $127. I'm guessing you're going to have to pay more for a warranty. Read carefully the fine print with regard to warranty coverage, if there is any coverage at all.