Hi. I have a 99 CRV and it is eating primary O2 sensors. I am on my fourth one. When I replace it, the car throws no ODB codes. But two to six months later, the O2 error returns, like clockwork. I have used both aftermarket and Honda sensors. What could be causing this? Thanks.
An O2 code does not necessarily mean the O2 sensor is faulty. It only provides a starting point for a thorough diagnosis.
If the sensors are really failing then something is killing them; coolant entering the combustion chambers, overly rich fuel/air mixture, oil consumption, etc, etc.
So what code, or codes, are being thrown?
Like ok said, what o2 code is it? Not all o2 sensor codes even refer to a fault in the o2 sensor. There’s a lean/rich code as well, which indicates either a combustion problem or an opening in the exhaust system before the o2 sensor.
I’ll double check the codes, but I think they were real. At least, replacing the sensors always fixed it. I’ll double check the codes and get back to you. Not near the car right now. I would expect the conditions you describe to throw other error codes too, no?
Not necessarily. There is no code for “crack somewhere in the exhaust.” You have to troubleshoot using codes as a guide.
I guess I assumed the shop would check for things like that the two times I had them do it (two different shops. one was a dealer).
Never assume that, especially with dealers. A lot of modern shops think the computer is their diagnostician, and have forgotten (or never learned) how to diagnose problems for themselves. I had an uneven surface on the front hub of my (then) new Acura TL several years back, and it took FOREVER for the dealership to fix it, because of course there is no computer code for “the freaking hub isn’t true,” and since they couldn’t find a computer code, they were trying to tell me that they can’t do any work under warranty. I ended up having to go to corporate and having them call the dealership to tell them to replace the hub.
I wonder what percentage of mechanics out there really understand ODB.
Those codes (almost?) NEVER directly say a particular part is bad.
What shop is going to continue digging if the part appears to fix the problem? Imagine getting a bill where they say “O2 sensor fixed the problem but kept digging for root cause- here’s your bill” Most times it fixes it. This is more rare situation. When you switch horses mid-stream, the new shop is starting over. That worked against you IMO. Like OK suggested, look for sources of pollution harmful to O2 sensors. Well documented online…
I’m in agreement wiht TwinTurbo. While it’s distasteful to change a part without really knowing, a mechanic is often standing there with a car that he’s never seen before and has no idea of the maintenance history or anything else on that vehicle.
At some point the cost of going through diagnostics for a dozen different things will become extremely expensive and a customer will likely be very upset if told they would have to be billed for X hours to check everything out.
Many years ago Subaru was having a problem with a lean surge condition. They had various modifications that were done under warranty and these modifications paid about 1.3 hours to perform them all.
In their service bulletin Subaru stated that a number of things were to be inspected BEFORE doing those mods but Subaru would not pay for those extras. Those extras required about 3 hours or so extra labor and involved checking valve lash, compression, EGR operation, fuel pressure, and about 6 or 7 other things.
It’s not difficult to see that a mechanic working on flat rate is going to balk at doing 3 or 4 hours of work for free before getting into the 1.3 hours.
While at a service school I actually posed the question of who was going to pay for it to the service instructor.
This made him a bit disgruntled at me for bringing this up in front of the class but it was fair question in my opinion. He refused to answer other than mumbling that the 1.3 “should be enough to cover all of that”. When I mentioned that the 1.3 was broken down mod by mod time-wise and did not take into account all of those extras he changed the subject and decided enough time had been spent on lean surging… 
2 different shops, 4 o2 sensors. Someone had the car in at least twice and went with the code the second time anyway, replacing the sensor they’d just replaced. Sorry, at least one of the mechanics screwed up here.
That could be but if the sensors are legitimately being killed by something else that leads to scenario of how much time and money does the customer want to spend hunting down the O2 killers.
Checking the compression is a first step must with any engine performance problem (along with plug replacement) and that would be one of the first expenses in the string. Seeing as how this is a '99 CRV the next expense could be a valve lash inspection and adjustment if an anomaly shows up, followed by a compression test follow-up.
After that, who knows…
The OP says the sensors last 2 to 6 months and that’s plenty of time for some other influence to do them in. This leads back to whether the OP would authorize a repair order stating to check X number of things first at X cost. Most would balk.
Can also be an “IFFY” connection in the wiring to the ECU…Sounds silly right? I thought so too when I had a similar issue on a Nissan Maxima…Beautiful vehicle…no accidents, no major services performed and it would reject ALL O2 sensor work…nothing seemed to work in the vehicle… I had to replace one of the wires going from the ECU plug down to the O2 sensor…the wire LOOKED fine…no corrosion, no evident breaks, no accident damage to wires or the like…the wire was just “BAD”…no continuity…so I replaced it and no problem since…happened last year round this time. Could be a connection getting made and broken unbeknownst to you…
Blackbird
Shadowfax the way I read it; took it to two different shops on first two failures. After that, OP figured why go in, I’ll change them myself and save some $. He says in the first post, “when I replace it”. Could be wrong but that was my first impression and a lot of people do just that. Hopefully OP can clarify.