Aging Post-Cat Lambda Sensor - Fault P0159

Hello, I thought I would pick the brains of the forum - I have done a search and cant see this question answered anywhere. I ran a durametric fault code check the other day and got an error: P0159 Porsche fault code 23 - 02 sensor ageing behind cat. c. bank 2 (cylinders 4-6). Its not causing an Engine Warning Light, but I plan to replace it anyway, as I understand it can damage the Cat.C if not addressed. Looking online, it seems I can buy the OEM Bosch part (0258006435) for £67 rather than the Porsche part 99660617801) as it seems to save almost £200 over the Porsche-labelled version of the same Bosch sensor. Haven't changed one before, will buy the proper tools - was going to order https://www.amazon.co.uk/Sealey-SX0...qid=1523520928&sr=8-1&keywords=Sealey+SX0320_ as it should make life easier. So my question is, should I replace the other sensors whilst I am doing this one? Have read online some people saying they should be good for 100k miles, others say change them every 30-40k My car is on 80k. I dont want to create work (or unnecessary cost) for myself, but also don't want to do a poor job. Would welcome thoughts......

If there are no faults coming from your other sensors then I wouldn't bother changing them. They have a set output that goes up and down within a voltage range and as long as they are still within that range I wouldn't touch them. Although the wrong mixture can result in damage to the cat, they're not so sensitive that they would be ruined by something that hadn't been picked up by the ECU/DME and given you a check engine light.

Also, they are frequently a total pig to remove. I did mine not so long ago and had to remove the cat pipe from the car and do it on the bench, cutting the end off the sensor so I could beat a socket onto it, and then use lots of heat and effort to get it out. I discovered it had been cross threaded, so had to chase the threads with a tap to restore them. The new sensors come with an anti-seize compound that you should definitely use.

Agree. I had my exhaust replaced last week and had to pay for 4 new sensors. The garage couldn't get them off the old cats, even with their tools. They said they would damage them taking them off. If I were you, I'd consider planning for new cats (at least used ones with the sensors removed already).

Thanks Martin and PHS - useful advice. Think I will plan to do just the one and hope I get it out, but if not will have to remove the cat and have another go or replace the Cat..... I have heard the sensor is a pig to get out..... Will get the proper tool and also assume I will need to break out a torch and heat it.... (not had a look yet, no doubt its painful to get too as well)

I had the same fault code a few weeks ago and advice I read was that if it was the first time and it reset ok then to leave it for the time being. I'm keeping an eye on it but it's been fine so far. Having looked at them when I replaced the back boxes I'll certainly echo that it didn't look like they were going to ever come out. I'm therefore planning to eeck them out for as long as possible then replace them all along with new Top Gear cats.

Thats interesting Grey996 - I think I can clear the code. Could then see if it reappears. As Martin said, if it isnt throwing a EWL, it cant actually be outside the voltage range.

That sensor ageing wont cause any issues with the cat .. the pre cat sensor can though . Ageing .. its old .. its got a slow signal .. the other one will be similar . If you fit only one then i expect in a few weeks time you will have a similar code but for the other side . Best to fit a pair . To be honest though .. you dont have an actual fault as such .. the sensor is there to check the cat .. save the planet stuff not anything to do with the vehicle running and its old .. hmm so am i .... But i dont need replaceing just yet

Thanks deMort - really appreciate the advice....... Based on what you and Grey have said, I think I will hold off on replacing it (I keep finding possible jobs and then talking myself out of them!) and reset the code and see what happens.

As has been said, I'd leave alone. If the exhaust is original then the sensors won't have ever been out and you'll have no chance of removing them without creating a lot of mess.

I replaced all of mine with the Bosch versions (not Porsche branded) and they are identical, plugs are perfect and I saved a small fortune. I was in the process of changing my cats for some 200 cells and I couldnt get the old ones out. I have the proper sensor sockets as well but even with heat and about 3 foot of bar on the end, I gave up because something was going to give before the sensors did. For me that was enough justification of their age and the fact that they had done very well and so I bought all new ones. I've just left them in the old cats as there was nothing really wrong with the sensors other than age and to get them out I will need to cut the harness off I think and use a full socket.