Looking for advice please £1500.00 Catalyst failure at 26,000 miles. Under extended warranty, and 6 months and 1500 miles ago Lambda Sensors failed and Porsche GB replaced under warranty. Serviced and MOT by Porsche only 400 miles later . Now Catalyst failed and replaced along with £350.00 Lambda sensors though they had only done 1500 miles. They say if Cat had been found damaged 1500 miles ago they would have considered replacing under warranty as collateral damage. They say "how do we know how the car has been driven, and if you have put in dirty petrol." (Always used high octane shell from same large petrol station )
Formal final letter on the matter says " Lambda Sensors are NOT known to cause a Catalyst to fail, however a defective Catalyst can cause a false indication of Lambda Sensor failure, and this is compounded by the fact that replaced Lambda Sensors
have to adjust ( in this case 1500 miles ) to a particular engines operating characteristics
and that is why it took 1500 miles before the engine warning light came on again"
Can any of this be possibly true, because on a google search its 100% that failed Lambda
sensors can destroy a Catalyst, and 1500 miles for new lambda sensors to adjust seems beyond belief..Thanks for any technical help and advice
Edited by Webmaster on 25/10/2008 at 14:38
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I read that the failed lambda sensor that causes engine to run too rich it can cause the catalyst to overheat and even melt. I suppose that this is more likely if you often take long runs.
That is stupid of them to say "how do we know how the car has been driven, and if you have put in dirty petrol." You should complain! So if my computer breaks they could say "how do we know you didn't make a big mean transformer, and plugged the computer to 380 volts"
My fiesta passed 160 000 km (100 000 miles) and it's catalyst works great and I did put dirty fuel on 2 occasions when my friend filled his diesel with petrol (a shame to waste it, is it :)
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however a defective Catalyst can cause a false indication of Lambda Sensor failure
...seems illogical if you are talking about the main lambda sensor; the one before the catalyst; that one has nothing to do with the cat.
and this is compounded by the fact that replaced Lambda Sensors
have to adjust ( in this case 1500 miles ) to a particular engines operating characteristics
Lambda sensors don't adjust; they are just 'sensing'. Only the computer can adjust.
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Thanks for your comments, very grateful as I'm trying to gather all the evidence I can to get the Insurance company who cover Porsche extended warranty to look at
just what crazy things porsche have had the audacity to put in writing in order to avoid
a warranty claim, perhaps they are feeling the "credit crunch" to have to resort to this
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It's actually pretty rare for a failed oxygen sensor to damage a cat - even allowing for the fact that most "failed" oxygen sensors are perfect and are changed for just telling the truth - why were yours changed.
It's even more inexplicable that a "failed" cat can cause a sensor fault. This smells of "poke and hope" diagnostics; ask your garage to justify their decisions on both occasions using hard evidence.
"Dirty petrol" - whatever that may mean - will have no effect on a cat. The instance in early 2007 was a silicone contaminant that only really affected JET and Total stations in the SE.
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Thanks for help..Engine warning light came on 6 mths ago. Porsche centre said sensors were faulty and porsche gave go ahead to replace under warranty, Couple of weeks ago engine light came on again, differant Porsche centre said Cat had failed and must be replaced together with Lambda sensors Total £1500.00 (incl £350.00 sensors) Asked Porsche to pay under warranty, they phoned talking about driving and dirty petrol etc, then wrote final refusal, saying failed sensors do not damage cats, damaged cats can give false failed sensors signals, and new sensors can take long time to adjust, in this case 1500 miles. I assume they are saying Cat had failed 1500 miles ago but only just showing as sensors take so long to adjust ..
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SGsheila
They are on desperately thin ice; threaten court action and they're unlikely to contest it.
Get a written report from the first garage as to exactly why the sensors were changed and what tests they did on them to prove that they had failed.
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I am not technical expert on this matter, but my understanding is that the car will have TWO lambda sensors.
One before the cat (to provide feedback to the engine controller and keep the mixture correct so that the cat functions correctly).
One AFTER the cat to act as a monitor on cat operation.
I do not see how a cat fault could in any way affect the FIRST sensor. If the cat were faulty then it would prompt activity from the SECOND sensor. Which sensor was changed?
I do not see why these sensors should take 1500 mile to 'adjust' - I think they operate as soon as they get up to temperature (about 300 degrees) and report a signal to the ECU. This signal can be read as live data on the diagnostic machine.
Sounds to me like they are trying to baffle you with science in the hope that you give up.
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It has 2 sensors before the Cat ( just one cat) and 2 after, Regret I dont know
which 2 were changed but I do understand they were the same 2 as they changed
6 mths ago. I would have hoped that items replaced under warranty that are supposed to have a minimum life of 50,000 miles (and often up to double that and more) should not have to be paid for after 6 mths and 1500 miles and if accepted as a warranty claim then would still be covered, thanks again for the advice
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