MAF, sensors and catalysts. = CEL

JohnCRS · Mar 7, 2023

Just recently I have had a couple of members experiencing a CEL engine light triggered by the exhaust sensors. In both cases this has been diagnosesd as failing catalysts, but the same can be triggered by a faulty MAF or oxygen sensor failure. Both were on 2006 cars.

In one case the catalysts and associated components were replaced at a substantial cost. It still took some time and hunting around to eliminate the CEL.
In the second case, since the emissions tested within limits, a work around was found to stop the CEL coming on

The point of this thread is to ask if others have had this problem and, if so, could you let me know the diagnosis and solution.

Many thanks, John

Motorhead · Mar 7, 2023

John,

A long while ago I seem to recall Richard Hamilton saying that the Lambda sensor’s sensitivity can be dialled-back (via PIWIS?), but that may have been for earlier Boxsters, the 986 perhaps?

I’m sure that the sensors age with time, so as a first step it might be prudent to replace them. It would be much cheaper than replacing the cats, and it would make sense to replace them anyway if the cats are being replaced.

Jeff

ralphmusic · Mar 7, 2023

Motorhead said:
John,

A long while ago I seem to recall Richard Hamilton saying that the Lambda sensor’s sensitivity can be dialled-back (via PIWIS?), but that may have been for earlier Boxsters, the 986 perhaps?

I’m sure that the sensors age with time, so as a first step it might be prudent to replace them. It would be much cheaper than replacing the cats, and it would make sense to replace them anyway if the cats are being replaced.

Jeff

You can certainly and easily check the sensor voltage with PIWIS and maybe standard OBD tester.

CLIFFWILKINS · Mar 8, 2023

Mine threw up the engine light running as normal I took it to a local Indy the code came up as the right cat. He deleted the code said it might have been a glitch on my 3 rd drive out bang engine light on again.

I took it to another Indy code was the same after extensive checks deemed the right hand cat was had it something to do with the warm up or something.

The price of a new cat was [

] expensive to say the least the other option was to put sports cats on but was told it could set the engine light off it would need a reflash but no guarantee.

My problem was my car has the cats built into the manifold an all in one job manifold and cat which further pushed the price up.

My solution I was lucky to find a good used manifold and cat still over £500 but a fair bit cheaper than new.

The guy that fitted it said someone had been chasing the dragon as that side had new oxygen sensors .

Touch wood all is fine now.

Motorhead · Mar 8, 2023

John,

Here’s a post from way back which might be of interest:

https://www.porscheclubgb.com/forum/tm.aspx?m=958060&high=Changing+o2+sensor

Jeff

CLIFFWILKINS · Mar 8, 2023

Interesting on above my light came back up after 3rd drive .

In my case 100% Cat one side even had a slight rattle when very hot.

JohnCRS · Mar 9, 2023

Thanks for the link to the other thread Jeff.

It does seem that you can spend a lot of money going round in circles until finally having to bite the bullet on the CAT, as Cliff has done. I would like to come up with an approach that reduces the number of hours spent on diagnosis, avoids replacing sensors or MAF whch are, in fact, OK etc. What are the signals of CAT failure? But it may be in the nature of this problem that this is just what you have to do.

If CATS do fail, has anyone gone down the aftermarket route? If you are having to spend £3-£4k to fix the problem, new manifolds and CATs, system from someone like TopGear may be an attractive alternative. No good if you want to keep OEM of course.

CLIFFWILKINS · Mar 9, 2023

Cheers John for me the key is to get it correctly diagnosed saving money.

The 2 nd Indy I used had a special diagnostic machine the guy operating it knew his stuff working on Ferraris for years before going to work at this indy he said it was 100% cat problem.

I am no expert on such matters but they hooked up to the car on idle for ages the temperature fluctuation was stable for a while within tolerance then spiralled up huge amounts which all pointed to that one side cat.

The other cat was stable all the time.

Moral is get it checked rather than trying the cheaper routes replacing parts that may not need changing.

It's was a doddle to fit because the previous owner had a new bolts nuts fitted on the entire exhaust system.

But in hindsight I unknowingly bought the car with the issue he obviously knew about the problem. My eng light came on my 3rd drive and the with new oxygen sensors fitted on that cat it was proof of a problem before I purchased it. Hey Ho.

Fault code PO431