2001 Integra LS, B18B1 engine type.
Service manual says the primary oxygen sensor is located in the B exhaust pipe, not the TWC. Acura parts guy says both 02 sensors are on the TWC.
Which is it?
Here's why I ask:
Midas replaced the B exhaust pipe. The MIL came on 2 blocks out of the shop, and they said the code "indicated a problem with the H02S". Geniuses reset the ECM, didn't troubleshoot the problem. The MIL came on again after driving about 5 miles. Of course Midas categorically denies they could have broken the H02S. "It's nowhere near the B pipe."
NEVER go to Midas.
-Al

 

the oxygen sensor is on the a pipe not the b. the b pipe is the pipe after the cat to the muffler section. midas is right.

 

Ok, since it's the primary o2 sensor it would be the one closest to the head on the piping. Get under the car and look for yourself.

 

They probably never plugged it back in. I've had similar experiences with midas.

 

All points taken, especially the one about getting under the d--- car and looking for myself. Tough to do while parked on a NY city street, though. I'll try to find a parking lot.

Can't say Midas is RIGHT yet. They didn't say it was the primary H02S. Just "the H02S." The secondary is close to the B pipe, no? I hope the suggestion that they just need to plug it back in works.

So I'll quote directly from the service manual to explain my confusion:
"The H02S is installed in TWC housing (B18c1, B18c5 engines) or exhaust pipe B (B18B1 engine)." P 11-67. It must be a typo; makes no sense for the primary to be pre-cat.

Thank you all.

 

Oops, I meant "makes no sense for the primary (H02S) to be POST-cat."

Sorry.

 

most of the time the upstream O2 is on the header. however my car has both on the cat. I've never gotten a good explaination for this but I believe the CA-spec integras have the upstream (#1) O2 on the header, however I think most of the integras are CA spec, even many of the ones that were sold outside of CA.

 

2001 LS

One should be on the "header" pipe near the "tunnel" where you would stick your arm to get the oil filter out.

the secondary o2 sensor should be on tail end (after the catalyst) of the cat.

not on B-pipe.

 

Took it back to Midas, resolving to get the exact DTC. Midas said it was PO141 (O2 Sensor Heater Circuit Malfunction Bank#1, Sensor#2). And they reiterated that there was No Way replacing the B-pipe could have messed with the secondary HO2S. They showed me the sensor locations while the car was up; secondary looks to be off the rear of the cat, but quite close to where the B-pipe is bolted in. I remain skeptical about the impossibility of doing damage while yanking off the pipe.

Anyway, I'm thinking of going to the dealer to have the heater circuit tested first, hoping it could still be a loose wire, rather than throw $267 + labor at a new sensor.

Oh yeah, Midas also told me the MIL will automatically come on after 50k miles if I don't replace the oxygen sensors, which don't last more than 50k miles. What?

 

midas is full of sh!t when they speak of that 50k mile stuff.

theres plenty of places online that sell NGK 02 sensors with honda connectors for weellll under 100 dollars. and its easy to change yourself.

stop going to midas and go to a privately owned honda service place.