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Volvo S70 oxygen sensor

I have a 1999 Volvo S70 stick shift with 130,000 miles. The “check engine” light has been on for the past 5k miles and my mechanic says it is definitely the oxygen sensor that needs replacing ($600 w/parts+labor). My question is can someone (i.e. me) with very little mechanical savvy buy an oxygen sensor and replace the current one for a lot less $$ w/o risk of damaging the car? If so, who is a reputable seller of o2 sensors and where can I find an install guide online?

O2 sensors are generally easy to change. The only problem sometimes is access on some of them or they may be difficult to remove from being in place so long.

There are only a few manufacturers of O2 sensors (Bosch, Denso, etc.) and a sensor from any established parts house should be fine.

Now the sticky issue. The O2 sensor (your car has more than one) has to be about the biggest whipping boy on Earth and faulty or not gets the blame for every ill, even by mechanics.
There are a number of things that can cause an O2 to generate a code but that doesn’t mean the O2 is bad.

Before buying any parts I would suggest getting a parts house (AutoZone, Checkers, etc.) to scan your car. It only takes a few minutes and they will do this free. Post any code or codes back for discussion.

So three codes were generated when I took it to PepBoys.

P0135 - 02sensor heater bank1 sensor 1
P0130 - same as P0135?

Any ideas what these codes could mean?

I don’t have a Volvo wiring schematic in front of me but the odds of having heater circuit failures on multiple O2 sensors are very very slim.

This would point to a power supply or ground problem for the heater circuits. I do not know how this particular model is wired up but if it’s a fused circuit then all fuses should be examined. (owners manual may show this)

If the circuits are not fused they may be drawing their power supply from the ECM (computer) or they’re losing their grounds through the ECM. This will require a wiring diagram for a look-see.

Autozone. About $80 for a Bosch O2 sensor. They’ll even lend you the tools you need at no cost, show you on their computer where the offending O2 sensor is located, and tell you what to do to change it. Job is less than an hour’s work and not that dirty, either (no grease involved). Your mechanic is no friend.

I just replaced what I believed to be the offending o2 sensors, but am still getting codes P0135 (bank 1 sensor 1) and P0136 (bank 2 sensor 2). Are there actually four o2 sensors and could I mistakenly have replaced the o2 sensors on the wrong bank? How do I know which bank is which?