Oxygen Sensor Fuse?

[DylanFulton]

Just replaced my bank 1 sensor 2 O2 sensor. I'm still getting a P0036 heater circuit code/P0141 heater circuit malfunction code. I'm hoping it's just the fuse/relay is blown and not something more in depth. I've done some searching and can't find where it's located. Any idea of the fuse/relay location and number? Thanks in advance

[DylanFulton]

Bump


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[emilio]

if i recall, the O2 sensors run through the fuel pump or engine electronics relays and share a fuse with the ECU and other stuff. if the relay or fuse were out you'd be getting a lot more codes. i'll double check the wiring diagram later today.

- emilio

[audinutt]

What o2 sensor did you buy and use? You replaced the sensor after the cat on bank 1? You're sure? What engine and which side did you change driver's or passenger's side?

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[audinutt]

Should be passenger side after cat

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[DylanFulton]

Should be passenger side after cat

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That's correct, and I used an OEM sensor.

[audinutt]

Oem? Denso? Bosch?

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[DylanFulton]

Oem? Denso? Bosch?

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It was Bosch

[DylanFulton]

if i recall, the O2 sensors run through the fuel pump or engine electronics relays and share a fuse with the ECU and other stuff. if the relay or fuse were out you'd be getting a lot more codes. i'll double check the wiring diagram later today.

- emilio

Would you mind sharing your wiring diagram?

[emilio]

sure - strap in if you've never read a VAG diagram before! note that the header says "A4", but this is the BHF diagram - these are all A4's to Ingolstadt.

J17 is the Fuel Pump Relay, which should actually be called Half The Engine Relay. that connects the battery to numerous engine electronics via fuse S234; if this fuse were out you would lose a lot more than O2 sensors. that connects via box #62 (those numbered boxes match up to the numbers along the bottom of other pages)...


...to box #26 that leads to tons of engine electronics, including boxes #118, 125, 132, and 139...


... that supply the other side of the O2 sensor heaters:



- emilio

[emilio]

[DylanFulton]

Lol, thanks very much

[micmckee]

Going to bump an old thread because I'm getting a similar issue.

I've been getting a code on startup Heater Circuit Malfunction: Open Circuit.

I replaced the bank 1 post cat O2 sensor (the one it specified) with an OEM one this afternoon and am still getting the code.

Any thoughts or ideas as to why replacing the sensor would still net the same code?

Cheers,

~Mic

[micmckee]

Might have misspoke, the old code was Warmup Catalyst; Bank 1: Efficiency below threshold now that I think about it.

So that lead me to bank 1 sensor 2 because that's post cat. Now that it's been replaced I'm getting the heater code.

[TruS4]

Pump

What was the fix for P0036 heater circuit (below threshold code)?

[Demma]

Anybody fix this issue?