Are my business assumptions correct?

Depends on the shop. Is it one you've used before and know the owner? If so, good chance you can just tell him you wanted to put them in yourself and could not and need his help. An honest shop will charge you a fair rate for labor.

What makes you think the oxygen sensors have anything to do with your problem? If you're getting errors saying that sensors are out of range, it might well be because they are accurately measuring an exhaust that is out of range. Especially if you're seeing more than one.

If you take O2 sensors to a shop and tell them to replace them, they will replace them. Depending on how they are feeling that day and if they like you, you may get a PIA charge for bringing in your own parts and being a pain in the ass.

This means that if your problem is not bad sensors that you have just wasted a lot of money, both in the parts you bought unnecessarily and in the labour you paid them to do unnecessary work.

Replacing the sensors could be trivial or it could be a major pain in the neck depending on how rusty things are and how well-kept things are. If the last person that changed the sensors used anti-seize, it will greatly reduce the work needed.

But before I'd go swapping parts at random, I'd make sure that I knew what was actually wrong. A shop that is truly honest is likely to tell you they won't do any work without spending time on a proper diagnosis first.

--scott

On Fri, 02 Apr 2021 14:25:42 -0400, micky posted for all of us to digest...

Depends on the shop. They make a small profit on parts. I am just giving the other side of the story... What happens if the parts you supply are incorrect, broken, poor quality, out of specs, what happens then? Are you sure the sensors are bad? Just asking. Maybe a bad cat or broken wires, misinterpretation of data. Use OEM or OEM supplier sensors or you may have another set of problems.

They can be in REAL inaccessible places and tough to remove. It depends.

Just like a lawyer would say: It depends. ;)

It varys with the shop.

Not honest so much as operates that way.

Some do, some don't.

If they had any sense they wouldn't because that would stuff their reputation if it went bad because they did that. But the worst of them don't care about stuff like that.

That varys even when they supply the parts.

micky snipped-for-privacy@fmguy.com wrote

Its very unlikely that more than one has failed.

It's very unlikely any of them have failed. I cannot even count the number of times I have seen cars blowing black smoke out the tailpipe which have just got new oxygen sensors because the computer was throwing a code saying the sensor was out of range in the rich direction.

The morons don't bother to figure out why it threw the code, they just swap out parts at random. They love swapping parts out.

--scott

The time honored redneck method is to find a shallow ditch to drive the car onto. Then, there's room to crawl under it.

In city ghettos, poor folks used to drive one side of the car over the curb, thus elevating the side you need to access. I (and my uncle) completely overhauled a 1957 plymouth using this technique. The lot was steeply sloping and that helped too. We replaced crank and rod bearings, pistons, rings, seals, etc. But, we did the valve job in the gravel driveway since it could be done from the top.

Naturally, these are only options if the car is still in somewhat running condition, or you have lots of neighbors to push the clunker into position.

When my truck had codes showing all four Oxygen sensors were suddenly bad, it indeed turned out that the damn computer itself had failed. The dealer installed a new ecu. It burned out within 2 blocks. They finally installed yet another, but also replaced all the wires to the O2 sensors. It's still running after 5 years now.

This truck isn't used much, so I think the damn rats probably chewed up the wires. They ate all the original insulation around the battery too :) The dodge ECU couldn't handle the short circuits. A piss poor electrical design I reckon.

The shop I use for stuff I don't do myself doesn't care. But then I buy my tires and have other work done there.

Well you can piss money away by changing the sensors but it's not going to clear those codes. You have a different problem.

As to what the shop does, it depends on the shop. In mine if a customer brings their own parts, they are installed with no testing or warranty given because those are the parts YOU want installed. It is also noted on the paperwork that "Customer supplied parts installed per their direction" That way if the parts are wrong or don't fix the issue it's not my problem. No difference in the labor rate.

Now a good shop would bring in the car, do an actual diagnostic on it, then repair the real issue, which in this case could be nothing more than a broken vacuum fitting or bad intake boot that is letting excess air in past the MAF. Or a skewed MAF that is reading a low GPS number and the PCM thinks it's getting less air than it really is. Fuel trims and O2 live data would show that and changing the sensors will do nothing. Also you may wish to know that the only sensors involved with those codes are the two upstream sensors, the downstream units are for testing the cat efficiency and as back-ups to the upstreams if they fail.

Yep, I love the ones who bring in a vehicle and say "Here I want XX changed, I know they are the problem" Instead of actually doing a diag and finding the real issue. They always seem to complain though when it doesn't repair the problem...

It always amazes me how people think that a *code reader* is the be all and end all of engine diagnostics. They seem to think an understanding of what's going on under the hood is no longer necessary. Unfortunately the diagnostician needs a very good understanding of system operation else they will be continually replacing bits which are showing

"But I saw on the Internet that replacing the front bumper will fix the rough idle problem!"

--scott

On Sat, 3 Apr 2021 19:02:02 +1100, Xeno posted for all of us to digest...

Parts cannon >>>>>>>>>>>>>>>>>>>>>>>>>>>>> $$$$$$$$$$$$$$$$$$$$$$

On 3 Apr 2021 14:49:40 -0000, Scott Dorsey posted for all of us to digest...

Really? I thought it was the rear bumper because that's where the exhaust comes out...

I'll post a whole new thread about this later, where everyone will see it, but it turned out it was none of the 02 sensors. But I hadn't replaced any either. I fixed it myself but it took me 3.5 years!