My 94 850 Turbo Wagon recently posted codes 435 and 443, which refer to the front O2 sensor and the cat (can't remember which is which). I'll check about vacuum tubing leaks (possible reason for setting codes), but with 110,000 miles on the original sensors, I'm inclined to replace them any way. My questions are:

1. Has anyone gone the universal sensor route, and if so, where did you get it?

2. Shoud I replace the rear sensor as well? Has anyone relaced the rear O2 sensor, and if so where did you get it (except for Volvo)?

3. If the cat code doesn't go away when the O2 sensor is replaced, how do I test the cat?

A few months ago I started getting the 153 code that indicated a rear O2 fault code and I had my indie mechanic replace it with a universal 4-wire Bosch sensor. This is a much cheaper fix than the OE Volvo O2 sensors that come with wires and connectors and my indie mechanic has done this to a few Volvos before and never had a problem. Lo and behold, the same code would come back almost every other day after I reset it. For some reason there was too much resistance going into the circuit and the ECU kept thinking there was something wrong with the O2 even though it was brand-new. We re-soldered it and rechecked the wiring several times and eventually was left with no choice but to replace it with the OE Volvo O2 sensor. This final move solved the problem and the code has not come back since. I'm sure there are plenty of owners who have gone the universal route and got it to work - I'm just pointing out that it might not work, as in my case. Maybe there was something wrong with the wiring or connector in my case and hence, replacing just the sensor did not fix the problem - I know it's rare, but just be on the lookout.

Hi,

My '94 850 turbo had the same O2 code. I found a generic 4 wire

sensor from Bosch at Auto Zone. Bosch #15717. Spliced it in, reset

the check engine light and it fixed the problem. It cost $49.95

vs. $200 from Volvo. I couldn't be more pleased.

Good Luck

Rod Brehm

Thanks, that's what I was looking for. I think I'll do the front one first, and in a couple of weeks, do the rear one. I been told by several people that the front and rear O2 sensors are the same except for the wiring, so I'll go the universal route.

Do you remember or have written down the wiring

combo that worked with the Bosch sensor?

Would like to have it in the eventuality mine

pulls the same trick.

Thanks

For a while, I kept getting the front O2 sensor sweep from full rich to full lean slow over and over and over again. What an engineering friend did was explain why it failed, and how to fix the problem.

Since I already spelled it out in length already, and it was deemed not fit to archive, I will keep that part as short as possible, and go to the fixing part.

If it is determined that an O2 sensor is not functioning properly, often it is because of contaminants on the sensor itself, usually from the combustion of low quality gasoline.

Now, to clean the sensor off, remove it from the exhaust line, heat it with a torch till it glows orange. Keep it glowing orange for atleast 2-3 minutes. Then, wait till it cools enough so that should you spray non-chlorinated brake cleaner on it, that it doesn't sizzle. Then, using some non-chlorinated brake cleaner, spray it down. At this point, you will see lots of black crud coming out of the little seams in the O2 sensor guard. Then, wait a couple minutes, and blow torch it again.

If you specifically have the slow sweep, what you might also want to do is open up one of the seams.

I did this to my front O2 sensor about 1.5 months ago. Before then, I would pull the code every couple weeks. After a while, it started pulling codes every other day or so. And since I did this, I haven't pulled a code in 1.5 months.