XC90 T8 2017 sensor location

Pretribrapper · Post by **Pretribrapper** » 24 Aug 2025, 18:56

Does anyone have a link or a pic with a diagram of where bank one sensor 3 is located and possibly confirm if I can simply use any downstream sensor as a replacement or if I need a specific form of downstream sensor other than specific to volvo xc90...
Hope this makes sense.
Basically hoping to find location on vehicle and part number I need. My code was P0042

Pretribrapper · Post by **Pretribrapper** » 25 Aug 2025, 18:54

Here are some additional pics but I can't tell which sensor is bank 1 sensor 3. Looks like I have 2 downstream sensors..

Vova585 · Post by **Vova585** » 25 Aug 2025, 19:14

I went to Volvo oem parts and put 2017xc90 t8 in search. Them emissions system. Search came back for 3 o2 sensors. They were upper, mid and rear. 2 variants of rear sensor based on spec code were offered as well. I assume the rearmost sensor is your sensor 3.
https://volvo.oempartsonline.com/v-2017 ... components

Pretribrapper · Post by **Pretribrapper** » 26 Aug 2025, 12:22

Thanks. Looking at the actual catylitic converter, I see it has two o2 sensors attached to it so I am guessing they are both down stream and since the exhaust comes in from the right side of the converter and out the back, I am hoping the green wire o2 sensor on the driver side is actually bank 1 sensor 3. And the one on the passenger side (right) of the converter would be considered bank 1 sensor 2.

Vova585 · Post by **Vova585** » 26 Aug 2025, 20:32

Not sure.
Would be great to figure out the wires which are responsible for heater element. You would be then able to check resistance between those 2 wires and if OL- totally your customer with broken heater element. Unfortunately it looks like those new sensors are 5 wires and I am not sure what they are(used to be 12v positive and 12 negative for heater, extra ground, signal wire in case of 4 wire sensor).

looks like #6 is your rear sensor.
https://www.volvopartswebstore.com/show ... y_make=865

Pretribrapper · Post by **Pretribrapper** » 27 Aug 2025, 14:18

That was awesome thank you. I did replace #6 and part number that worked was 31370964. I did buy on Amazon for $91 but I picked up a couple other ones that say downstream and are compatible but they were not. The connector up at the plug had a stopper in it to prevent the wrong plug. All other ones I used were wrong plug.
Oddly I dont have a #4 that I see anywhere. I only have the #2 I think and they both look to be downstream. No idea where the upstream is.
I did install and reset the CEL but I do still have a P0042 permanent fault for bank 1 sensor 3. I am told I will have to do a few drive cycles to get it to clear if indeed it is corrected

Pretribrapper · Post by **Pretribrapper** » 27 Aug 2025, 14:19

Vova585 · Post by **Vova585** » 27 Aug 2025, 15:23

Sorry, but with amazon or ebay parts you are playing Russian rullet with 1911.
Also it is not true for heater code to be present after code erase and sensor replacement. You may have a readiness monitor not set, but no immediate code. So 2 possibilities- we replaced the wrong sensor, in case we replace the correct sensor and the code is immediately present-wiring prior to the sensor is at fault.
I would vote to buy volvo oem wiring diagram subscription and look which wires are responsible for heater at sensor 3(will give you colors) and then check with 1 apm substitute load at the connector. Check resistance in corresponding wires. So dont throw your old sensor yet.
This sensor you replaced os 4 wires. So prior troubleshooting applies

Pretribrapper · Post by **Pretribrapper** » 27 Aug 2025, 18:34

So far looking good and seems to have worked. Thank you all.

Vova585 · Post by **Vova585** » 27 Aug 2025, 21:22

Well, the scanner data makes sense. Likely your evap and catalytic sensors still not fully tested by ecm to pass. Usually shpuld be 3 drive cycles or more depending on conditions.
So "codes found-0" is the most important thing. The heater element is working in the new sensor. Whether it will work as it should is a different question. I hope you are lucky with this sensor.