Post-cat O2 sensors - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Frodo · 08-13-2010, 03:44 AM

Come on, guys...SOMEONE must have some sage advice on this topic. Speak up!

landrovered · 08-13-2010, 04:46 AM

The answer is...it depends.

It depends on which error code(s) is being thrown. If you have the "slow response" code then no, If you have "failure" codes then the DME will kick the fuel curves to a more moderate setting (like limp home but not as bad) and you will not get the performance or economy that you would with the codes cleared.

My 3.6 has a tweaked DME and the difference in the curves is easily noticed, in a stock set up it may be less obvious but it operates the same.

So the answer is, replace your secondary O2 sensors if they are failing and then you do not have to suffer the issue.

Simply clearing the codes will give you a change in performance until they come back on.

gschotland · 08-13-2010, 05:12 AM

At 64k miles one O2 sensor went and it was replaced. At 70k at 2nd one started giving me intermittent CELs. I read here that it's best to change all 4 at once, so I changed the remaining three even though the car was running fine, and experienced a noticeable improvement overall in driveability.

O2 sensors tend to fail around the same time. If you're planning to hang onto your car for a while, best to just change them and get it over with, or they're likely to come back and haunt you at an inopportune time. I got them with the OEM type connectors from Maxspeed Motorsports for $99 each, which was the best deal out there at the time (last fall).

Frodo · 08-13-2010, 06:51 AM

Thank you.

The code was P 0159 which, I believe, is indicative of a sluggish response (vs a complete failure).

It's funny, some places I've read about replacing ALL of the sensors like every 30K miles...other places people have said they're supposed to last like 100K (I know this really is not very likely) and that one should only spend the bucks to replace the ones throwing codes and leave the rest.

Seems to be a lot of differing opinions out there!

boxzilla · 08-13-2010, 07:31 AM

Frodo ~ I agree, its a very personal decision. I replaced my 2 post cat units even though only 1 had thrown a sluggish code. When 1 of my pre-cat units threw a code, about 1 month later, I only replaced the 1 unit. The other pre-cat unit is still going strong.

If you have the $$ to replace all 4 and you are paying someone else to do it for you, then probably makes sense to pay for 1 install and get it done. Since I do my own wrenching, and most times you can find them for sale with free shipping...then why not just replace them as needed? I don't worry about running the car for a week while waiting for them to arrive as they only impede my mileage and pose no serious threat.

I was proactive and did replace my AOS at 70k since I was the second owner and did not have a service history, and feared the negative impact of a failed AOS was more significant than I wanted to experience. ounce of prevention vs. pound of cure scenario.

landrovered · 08-13-2010, 07:37 AM

I will put this out there for your consideration.

The pre cat sensors do the heavy lifting for the fuel injection system, they set the overall rich/lean mixture for the engine. If a pre-cat sensor was to fail on my car I would replace both.

The post cat sensors are only to confirm that the cats are working. They are not nearly as important as the pre cat sensors. I would replace them one at the time.

Also the only thing that makes it a "Porsche" O2 sensor is the plug (connector). They are bog standard Bosch thimble type O2 sensors and if you are willing to do some soldering you can buy them for $39 but you have to solder your Porsche plug to the wires.

Frodo · 08-13-2010, 07:52 AM

Quote:

Originally Posted by landrovered

I will put this out there for your consideration.

The pre cat sensors do the heavy lifting for the fuel injection system, they set the overall rich/lean mixture for the engine. If a pre-cat sensor was to fail on my car I would replace both.

The post cat sensors are only to confirm that the cats are working. They are not nearly as important as the pre cat sensors. I would replace them one at the time.

Also the only thing that makes it a "Porsche" O2 sensor is the plug (connector). They are bog standard Bosch thimble type O2 sensors and if you are willing to do some soldering you can buy them for $39 but you have to solder your Porsche plug to the wires.

Makes sense.

I thought about doing the standard/generic route but got lazy and ordered the plug-and-go ones, though I am planning on putting them in myself. It's not too tough, is it? I don't have the special 22 mm wrench...how hard is it if one uses an adjustable wrench??

BTW, I've read that you should crimp NOT solder. Don't know why...or even if it's truly an issue.