Hi, everyone. Hoping someone might be able to help me out. I have a 2006 Volvo S40 (2.4 I)

The trunk light keeps coming on the screen and now the engine light. I took it to auto zone and had it checked there. They told me it was the three sensors: oxygen sensor, P0031 Heater Control Circuit Low, and P0147 02 Heater Circuit.

Is it possible for the trunk light and all three sensors to go out at once or do you think this is an electrical problem? They all just went out at the same time, so I'm thinking it might be the latter. Other than that, there's no problems at all with the car. Everything runs perfectly.

Thanks in advance for any help!

 

I'm guessing the "trunk light" is one of two things - a bad sensor (the one that tells the car the trunk lid is open) or a bad latch (and your trunk lid IS open). Either way, it's got nothing to do with the other failures.

Those other failures sound like a simple O2 sensor failure, or possibly the supply circuit to the sensor. Check your owner's manual (download one if necessary) to see where that fuse might be.

 

Yes, the non-turbo cars have three O2 sensors. (turbo cars have 2) If your codes are all O2 heater codes - power for those heaters is from fuse 33 in the fuse box shown below. That fuse also powers the vacuum pump. A common failure is the plastic vacuum pump switch breaks, causing the vacuum pump to run all the time, and the pump eventually melts/seizes and blows the fuse - for the pump the the o2 heaters!

Disconnect the switch/vacuum pump (or fix it would be appropriate), replace the fuse and the heaters should work again and after codes are erased they will not come back. (as long as the O2 sensors are indeed ok) . You typically are not going to have multiple O2 sensor failures. Is your fuse 33 still ok?

 

your car has two oxygen sensors a front sensor and a rear sensor and each sensor has two circuits - a heater element and the signal. The P0031 is saying the heater circuit on the front sensor is at fault and the P0147 is saying the heater circuit for the rear sensor is at fault. So per hoonk's guideance, you should be looking for something common to both such as the power to the heating elements. Fuses, relay, wiring. Since your car is a 5 cylinder and not a turbo, you can see which fuses are in play.

 

Hi there! Thanks so much for all your guidance. I replaced the fuse and got a new vacuum pump since what you said was correct--they told me it had broken. However, when the new vacuum pump was hooked up it started making a loud buzzing sound even after the car is off and gets very hot. It won't shut off. Any ideas?

 

Turns out the fuse did go and I had to replace the vacuum pump but when I did the latter, the vacuum pump starts making a loud buzzing sound and gets really hot. It won't stop until I disconnect it. Any idea what's going on? Thanks again for all the help. You and the previous poster were great.

 

Yes the vacuum pump turn off switch is bad - that's what broke first and fried your old pump. The switch is part of the hose going to the brake booster. This MIGHT be the correct part, there are a couple of choices. Verify first - probably by using your local dealer to get the correct part number.

 

thank you so much for your help. also would like to know how to install the vacuum hose is there a site with pictures and directions.