I am certain it has been discussed a million times.....But I am going to TRY and clean the forward O2 sensor on my 1998 S70 tomorrow instead of replacing it. I have read and seen how many have done this successfully so might as well try it instead of spending the 200-300 dollars it costs for a new one. I have both a socket type and claw type O2 sensor tools so it'll only be a little hassle to change it out. Has anyone here successfully cleaned the upstream O2 sensor? Here is the code I get: P0133 so I'm not even sure its THAT sensor. I have also heard that the front or upstream sensor wont throw a code and only the aft sensor will. What is your experience?

 

P0133 is a "slow response" trim code which often gets blamed on on the o2 sensor. More often than not its caused by a vacuum leak somewhere. I'd be really surprised if cleaning the sensor will work. The notion the upstream sensor won't throw a code nonsense. The upstream sensor (before the cat) is used to set fuel trim - but fuel trim can be thrown off by air leaks that are beyond the sensor's abilty to correct - thus throwing an out of range code or a slow response code (as some trim codes are averaging). The rear sensor is used to measure cat efficiency via a differential calculation between the front/rear sensor. A bad rear sensor will throw a code but not impact engine performance (but a clogged cat will). Sensors also have two parts, a heating element and the measurement circuit. If you heating element fails (which the more common way the sensor goes bad), you will get a code plus the readings will be off and your performce is poor.

 

Where should I start to look for an air leak? Is there a routing diagram available online for the vacum hoses you can point me to? Thanks again.

 

which engine? Usually there should be a sticker under the hood on the usual places - ie firewall/fender/fan schroud. If not just google "vacuum diagram volvo s70" etc. You should also spray some carb cleaner around the air boots and the intake tubing. if the idle changes or the liquid sucks in, you found it. For the vacuum line, look around the vacuum tree (a plastic part which connects multiple vacuum lines. Look for missing end caps, cracked hoses etc.

 

Thanks, ill look for the sticker and also something to print. I have most BMWs and Dodge trucks, so the Volvo is new to me....thanks again.