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!

 

I would diagnose the problem and not replace a part because of a code. A code means the control unit does not like the signal that is is getting, not that a part is bad. And IF there was a bad O2 sensor I would replace only the part that was bad.

 

+1. A bit of background here: The two O2 sensors have totally different functions. The front sensor is the "lamda" sensor that tells the ECU the level of oxygen in the exhaust to control fuel trim (too much O2? send more fuel. not enough O2? send less fuel etc). The rear sensor is after the catalytic converter and its job is to monitor whether the converter is functioning normally and converting any unburnt hydrocarbons using what O2 is remaining. The ECU compares the rear sensor's signal to the front's and if it doesn't like what it sees, a code is set like a P0430 (cat efficiency error). The sensors used today have two circuits - one heats up the sensor the second provides the signal voltage. If the code tells you there's an issue with the heater circuit, then you either have a wiring/connector issue or a bad sensor. If the code tells you the signal is missing again it could be a wiring or sensor issue. If the code tells you the signal is "out of range", well that's where it gets interesting because its saying the computer can't adjust the fuel trim enough to bring the O2 levels into spec. That can be caused by a long list of things - intake air leak, bad fuel metering, incorrect fuel pressure, incorrect signals from another sensor etc. Quite often when the root cause is one one of these, you may also see a "happy meal" of codes. That's where an experienced tech will know what to do with some additional testing / investigating since the codes simple provide clues not answers.

 

Wow! 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?

 

ignition coils have nothing to do with the O2 sensor faults but the interesting thing here is both sensors show a fault which would lead me to check out wiring - starting with the ground connection to the exhaust.

 

Remember the diagnose rather than guess part? You have heater codes on BOTH O2 sensors, B1S1 and B1S2 - that is bank one (you only have one bank) Sensor 1 (front), and sensor 2 (rear). So what is common between the two sensors?

Looking at the wiring diagram - both sensor heaters are powered by fuse 33 in the fuse box 15/31 under the hood. Note that fuse also powers the brake vacuum pump. A common problem is the brake vacuum pump switch breaks, (if equipped) ,turning the vacuum pump on and it runs all the time until it overheats, melts, shorts out and blows the fuse. So the problem could be there is no power getting to the heaters due to a blown fuse caused by a melted/shorted vacuum pump and a broken vacuum pump switch. Do you have a blown #33 fuse? Does your vacuum pump work? (turn key on, engine off, depress brake pedal a few times - you should hear the vacuum pump buzz under the hood) Sample Vacuum pump and switch pictured below.

 

Thank you! I’ll start by checking the fuses and provide and update soon.

Appreciate all the feedback. You guys have been super helpful.

 

Hey, I have this problem with my 2006 s40 t5 awd manaul. Volvo mechanic said I can replace fuse but it will keep blowing until I replace both o2 sensors...so I did. The fuse kept blowing. But it sometimes takes weeks, sometimes days for it to blow out. I thought of replacing the vacuum pump switch or pump itself but there is one mystery.

Why does my car accelerate with jumping RPMs, with delay in acceleration and power when fuse 33 is not blown out with no check engine light?

Could this be related to a different issue because originally the acceleration delay started with fuse 33 being blown out and my o2 sensors not working according to the volvo mechanic.

German cars mechanic couldn't figure it out along with some other mechanics. Good times. 👍 perhaps they don't want to deal with it lol.

 

What brand O2 sensor was used?

The other possibility that springs to mind is that you could have a clogged catalytic converter due to a long-term misfire. That shouldn't blow a fuse in the O2 heater circuit though.