O2 Codes after replacing sensors

[lemoose]

A couple days ago, my service engine light came on and my reader pulled up P0135 and P0155 codes (S1, B1 and 2 heater circuit). Prior to buying replacement sensors, I cleared the codes several times throughout the next several days and each time the exact same thing happened:

Clear codes, P0135 hidden code pops up within a couple miles/minutes, then P0155 joins the party about within 10-15 minutes later along with the service engine light.

I mention this because given my limited experience wrenching, a code like this will at first trigger intermittently, worsening with the miles until it fails consistently/immediately. Whereas here, out of the blue, once the code tripped once, it kept tripping consistently. Given that my o2 sensors were at about 80k miles, I figured thats where I should start. However, the exact situation above continues to happen. Any ideas?

[lemoose]

Shameless bump…. The issue persists and im not sure what to check next.

[PSUEng]

I'm actually confused by your post--you got the codes, then replaced sensors, and same codes came back? Or, you replaced sensors and these new sensors are throwing codes? If your heating element is shot causing a slow response, you may simply be looking at new sensors. What you don't want are cat efficiency codes.

[Slideways]

Which replacement sensors did you buy?

Either it is a faulty sensor, issue with the wiring harness, possibly a fuse or lastly, the DME.

Try unplugging, plugging the sensor back in and making sure the connection is secure.

[lemoose]

I'm actually confused by your post--you got the codes, then replaced sensors, and same codes came back? Or, you replaced sensors and these new sensors are throwing codes? If your heating element is shot causing a slow response, you may simply be looking at new sensors. What you don't want are cat efficiency codes.

Same codes before and after the new sensors

Which replacement sensors did you buy?

Either it is a faulty sensor, issue with the wiring harness or lastly, the DME.

Try unplugging, plugging the sensor back in and making sure the connection is secure.

bosch-13949 and bosch-13952. Faulty sensor is possible, but both faulty sensors failing in a way indistinguishable from the two old sensors? The wiring looms on the valve cover look fine, but I haven't checked between there and to the DME, nor the DME itself. Thats the only thing I can think of too at this point but it seems like such an odd and rare failure point that I really want to make sure I'm not overlooking anything before going down that potential rabbit hole

[Slideways]

Same codes before and after the new sensors




bosch-13949 and bosch-13952. Faulty sensor is possible, but both faulty sensors failing in a way indistinguishable from the two old sensors? The wiring looms on the valve cover look fine, but I haven't checked between there and to the DME, nor the DME itself. Thats the only thing I can think of too at this point but it seems like such an odd and rare failure point that I really want to make sure I'm not overlooking anything before going down that potential rabbit hole

Those sensors are fine. Typically, the wiring between the sensor and the plug can get damaged, either by getting pinched under the beauty cover or burned by the exhaust manifolds. It is rare that the wiring is damaged between the plug and DME.

There might be a fuse for the O2 sensors that I didn't think about. Quick search brought this up - https://www.e46fanatics.com/threads/...-fuse.1288155/

[lemoose]

Ah good find! I'll look into this.

Big thanks!

[sapote]

Given that my o2 sensors were at about 80k miles, I figured thats where I should start. However, the exact situation above continues to happen. Any ideas?

Somehow this thread didn't catch my eyes.

As about the codes for both sensor heater circuits, I doubt the problem is related to the sensors, old or new as it's very rare for both to go bad at the same time.
Fuse F4 in engine box supplies to all 4 O2 sensors, and since no codes for post cat sensors, then I don't think it's a bad fuse.
Check the sensor pin1 Red/White wire for 12v with engine running or key turned ON. And during car running, pin2 Brown wire should be grounded by the DME to turn on the heater.

[lemoose]

Somehow this thread didn't catch my eyes.

As about the codes for both sensor heater circuits, I doubt the problem is related to the sensors, old or new as it's very rare for both to go bad at the same time.
Fuse F4 in engine box supplies to all 4 O2 sensors, and since no codes for post cat sensors, then I don't think it's a bad fuse.
Check the sensor pin1 Red/White wire for 12v with engine running or key turned ON. And during car running, pin2 Brown wire should be grounded by the DME to turn on the heater.

Thanks for contributing! I do have the post cat o2 monitors disabled (via the ecuworx tool option). Would that explain why im only seeing the precat codes? Ill try swapping in a new fuse tomorrow and keep everyone updated either way.

[Slideways]

Thanks for contributing! I do have the post cat o2 monitors disabled (via the ecuworx tool option). Would that explain why im only seeing the precat codes? Ill try swapping in a new fuse tomorrow and keep everyone updated either way.

If those are off, there is nothing to monitor/heat lol

Hopefully it is just the fuse.

[lemoose]

Solved! It was indeed the f4 fuse. Thanks all!