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Discussion Starter · #1 ·
So my 06 S40 has a code saying the O2 sensor (Bank 1 Sensor 1) is bad. If it matters the car has 209k miles and I just bought it.

While changing the spark plugs yesterday I noticed one of the ignition coils was busted (cylinder 4). It doesn’t say anything about a misfire, but I’m sure it’s not firing.

2 questions:
Would you replace BOTH O2 sensors, or just the one?
Should I replace the bad ignition coil first to see if that’s what’s causing the O2 issue?

Any other tips or advice would be awesome! Thanks!
 

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if you are getting unburnt fuel from a misfiring cylinder, it could choke up the o2 sensor with carbon, so yes, best to fix that issue prior to replacing o2 sensors. it may not cure the sensor, but it will stop the new one from going bad quickly.
 
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Discussion Starter · #3 ·
Thanks for all the input! I just double checked and the codes I’m getting are:
  • P0031 Heat Control circuit Low B1 S1
  • P0036 Heat control circuit B 1 S2
  • P0030 heat control circuit B1S1

So it sounds like once replace the ignition coils, if it still haze the same codes, then it is probably a bad Bank 1 Sensor 1 that needs to be replaced, since it’s the heater.

does that sound about right?
 

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yes, the volvo uses a 4 wire O2 sensor, 2 wires are the heater circuit (they heat the sensor up to operating temperature) this circuit is fused and I have had a fuse blow causing issues in the past, so make sure the sensor is recieving power to the heating circuit (on one of my volvos this circuit was separately fused from everything else under the dashboard, along with the fuel pump circuit, so be aware the fuse may be separate.
so from the looks of it it will be both the front and rear sensors on bank 1 (dont ask me which bank is which, so both the sensor in front of and behind the catalytic converter.]
 
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