Cats and O2 Sensors failing at the same time?

[mobblers]

For about six months my car has had an issue with the check engine light being on constantly and the car being a bit jerky when the engine is cold. The car has been looked at by Audi a couple of times and the only error codes that have been stored have been for running rich when cold.

The car is currently with Audi again for the same issue but this time I was told that during the readiness diagnostic check one of the front O2 sensors wouldn't pass the check and was therefore faulty and needed to be replaced. The O2 sensor was replaced and when the readiness test was run again the cat downstream of the new O2 sensor wouldn't pass the check and it, too, needed to be replaced. The cat was replaced and when the readiness test was run again the O2 sensor downstream of the new cat wouldn't pass the check and needs to be replaced. This is due to be done next week but Audi warned me that once the new O2 sensor is fitted the readiness test should move on to the other side of the exhaust system and it's possible that the same parts could fail to pass the readiness test and will also need to be replaced.

I have very limited knowledge on this but it seems odd to me that so many parts of the exhaust would all fail at the same time. Is it possible that there's something else going on that could be causing the readiness test to fail?

[Dinosroume]

Hey

Did you get the error running rich at idle? I used to have this error on Bank 2 rear lambda sensor and get the check light regularly and tried to change the sensor but it has stuck and need to remove the cat downpipe and try to remove it.I got the revo tune stage 1 in my rs4 b7 and the error disappear.

Cats sucks mate personally i'm planning to get milltek full exhaust with decat downpipes and revo stage 2 because rs4 lambda sensors are very sensitive and i don't like the engine light in my dash lol!

DINOS

[murph7355]

AIUI bad O2 sensors may cause the car to run rich. Which basically means unburnt fuel in the system.

And IIRC fuel can kill cats.

Not sure why they couldn't check the other side now or why both sensors didn't throw a fault in the first place though.

Never ignore CELs unless you know exactly why they are there.

I've had good service from my local Audi dealer/garage in the past, but am less convinced about using them as the cars get older as I'm not convinced they're as ready to do lateral thinking and definitively won't countenance using non-Audi parts.

[mobblers]

Not sure why they couldn't check the other side now or why both sensors didn't throw a fault in the first place though.

Never ignore CELs unless you know exactly why they are there.

I've had good service from my local Audi dealer/garage in the past, but am less convinced about using them as the cars get older as I'm not convinced they're as ready to do lateral thinking and definitively won't countenance using non-Audi parts.

From what Audi have told me, I think the readiness test works through each component in turn and the test stops if any component fails. This means the test hasn't actually got as far as testing the components on the other side of the exhaust so we don't know what state they're in.

I haven't been ignoring the CEL. Every time it comes on I book the car in with Audi to be looked at. Unfortunately, I need an appointment with a loan car available and it usually takes 4 to 6 weeks to get one which means having to drive the car for that time with the CEL on.

I agree with what you say about using Audi for repairs but the dealer is very close to where I live and they can provide loan cars which makes life much easier for me.

Did you get the error running rich at idle? I used to have this error on Bank 2 rear lambda sensor and get the check light regularly and tried to change the sensor but it has stuck and need to remove the cat downpipe and try to remove it.I got the revo tune stage 1 in my rs4 b7 and the error disappear.

Cats sucks mate personally i'm planning to get milltek full exhaust with decat downpipes and revo stage 2 because rs4 lambda sensors are very sensitive and i don't like the engine light in my dash lol!

DINOS

The CEL only comes on when the engine is warm and after a long drive. Once the CEL is reset by Audi it doesn't come back on for a while because most of my driving is short local journeys (not ideal for the car I know). The running rich while cold doesn't seem to cause the CEL to come on.

When Audi replaced the first O2 sensor it was stuck, like yours, and they had to remove the cat to be able to get enough leverage to remove the sensor.

I did think about changing the exhaust but I'd like to keep the car stock if possible.

Thanks for the replies.

[Dinosroume]

Get high flow cats only , audi parts ain't cheap . 1213.23 usd left cat , 1105.45 usd right cat prices are from ECS tuning.
My car because of the lambda problem as i told you destroyed one rear lambda because it war running rich and have a lot of unburned fuel.

In my opinion get 4 new lambdas from bosch not oem because when i asked the dealer here in my country greece the best price for front lambda was 240 euros each, and i got the bosch for 190 euros both , and find someone to install you high flow cats in your oem exhaust.

I can give you part numbers if you want.

DINOS

[ArthurPE]

How many miles on the car?
Sounds fishy about the sequential check stopping at the first fault. So after cleared it stayed off for a while? So it MUST have made the check on the other side (and apparently no codes).
The upstream O2 is the control sensor, it modulates fuel pressure to maintain A/F ratio. Its output can be monitored with their scan tool.
The downstream monitors the cats efficiency.

Cats usually are good for over 100k miles or more.
Sensors about 50-75k, if the car is running right much longer.

[mobblers]

How many miles on the car?
Sounds fishy about the sequential check stopping at the first fault. So after cleared it stayed off for a while? So it MUST have made the check on the other side (and apparently no codes).
The upstream O2 is the control sensor, it modulates fuel pressure to maintain A/F ratio. Its output can be monitored with their scan tool.
The downstream monitors the cats efficiency.

Cats usually are good for over 100k miles or more.
Sensors about 50-75k, if the car is running right much longer.

The car has 54,000 miles on the clock. To be honest I was a bit sceptical about the cats failing until I read online that running rich can damage cats and my car seemingly has (or had) an issue with running rich when cold (possibly caused by a faulty O2 sensor?).

As far as the sequential check is concerned, it's quite possible that I misunderstood what the Audi service rep told me but they supposedly didn't know (or couldn't confirm) that the first cat needed replacing until they had replaced the front O2 sensor and re-run the sequential check. Similarly, once the cat was replaced and the test re-run, the faulty downstream O2 sensor came to light. From that I just assumed that the test stopped after it hit an item that was failing. However, I'm just guessing since I have no idea how the test actually works.

[ArthurPE]

54k is too soon
Especially since you were taking it in and all they did is reset the light. Not sure about the UK but the US requires by law an 8 yr/80k mile warranty on cats. Check into it.

What is mpg on the highway? Overall average?
Do you get a rotten egg smell under load?
All cars run rich until warmed up, direct injection more so.

I would argue for some sort of goodwill from them.
I doubt the cats are bad.
Does it pass your MOT inspection? (If they do a sniffer test).
It's easy to tell if the call works, put a exh gas analyzer in front and back and compare readings. They can also pull the sensors and use a vacuum gauge to see it it pluugged. They should do that rather than replacing everything.

[Dinosroume]

Not sure why they couldn't check the other side now or why both sensors didn't throw a fault in the first place though.

Never ignore CELs unless you know exactly why they are there.

I've had good service from my local Audi dealer/garage in the past, but am less convinced about using them as the cars get older as I'm not convinced they're as ready to do lateral thinking and definitively won't countenance using non-Audi parts.

From what Audi have told me, I think the readiness test works through each component in turn and the test stops if any component fails. This means the test hasn't actually got as far as testing the components on the other side of the exhaust so we don't know what state they're in.

I haven't been ignoring the CEL. Every time it comes on I book the car in with Audi to be looked at. Unfortunately, I need an appointment with a loan car available and it usually takes 4 to 6 weeks to get one which means having to drive the car for that time with the CEL on.

I agree with what you say about using Audi for repairs but the dealer is very close to where I live and they can provide loan cars which makes life much easier for me.

Did you get the error running rich at idle? I used to have this error on Bank 2 rear lambda sensor and get the check light regularly and tried to change the sensor but it has stuck and need to remove the cat downpipe and try to remove it.I got the revo tune stage 1 in my rs4 b7 and the error disappear.

Cats sucks mate personally i'm planning to get milltek full exhaust with decat downpipes and revo stage 2 because rs4 lambda sensors are very sensitive and i don't like the engine light in my dash lol!

DINOS

The CEL only comes on when the engine is warm and after a long drive. Once the CEL is reset by Audi it doesn't come back on for a while because most of my driving is short local journeys (not ideal for the car I know). The running rich while cold doesn't seem to cause the CEL to come on.

When Audi replaced the first O2 sensor it was stuck, like yours, and they had to remove the cat to be able to get enough leverage to remove the sensor.

I did think about changing the exhaust but I'd like to keep the car stock if possible.


Did you refill your car with race fuel or octane booster?
Thanks for the replies.

Did you refill your car with race fuel or octane booster?
Common problem in cats and lambda sensors.

[mobblers]

54k is too soon
Especially since you were taking it in and all they did is reset the light. Not sure about the UK but the US requires by law an 8 yr/80k mile warranty on cats. Check into it.

What is mpg on the highway? Overall average?
Do you get a rotten egg smell under load?
All cars run rich until warmed up, direct injection more so.

I would argue for some sort of goodwill from them.
I doubt the cats are bad.
Does it pass your MOT inspection? (If they do a sniffer test).
It's easy to tell if the call works, put a exh gas analyzer in front and back and compare readings. They can also pull the sensors and use a vacuum gauge to see it it pluugged. They should do that rather than replacing everything.

Just to update, once the rear O2 sensor was replaced the sequential test completed successfully and no other parts needed replacing. I have the extended warranty which covered the two O2 sensors and the final bill came to slightly less than the cost of the Cat. They didn't charge me for any labour or for the cost of removing the snapped studs in the exhaust manifold. It was a fair amount less than I was expecting so I'm quite happy about that. The car is back and does seem to be running better than before and I think the mpg is also better although it's only been a few days so can't be certain.

The car did pass the MOT (last December) but the only way they could get the correct lambda was to rev the guts out of it. The CEL was on at the time but they passed it anyway since the car was going in to Audi the following day to be looked at.

From what I can tell the cat warranty in the UK is the same as in the US but since the car is more than 8 yrs old the cat wasn't covered.

Did you refill your car with race fuel or octane booster?
Common problem in cats and lambda sensors.

I've only ever used Shell's premium unleaded petrol (V-Power at the moment). Ive never used anything else or any additives either.

[Rusty Racer]

I believe you need to view the lamba sensors as a service item as they do age and eventually fail. If you want your car to run and perform like new they are well worth changing imo. After the initial cold start map is replaced they are guiding the ecu as to how much fuel is in the exhaust. Bad sensors are slow to react and if the ecu is in any doubt it will run rich which gives its own problems...

[ArthurPE]

54k is too soon
Especially since you were taking it in and all they did is reset the light. Not sure about the UK but the US requires by law an 8 yr/80k mile warranty on cats. Check into it.

What is mpg on the highway? Overall average?
Do you get a rotten egg smell under load?
All cars run rich until warmed up, direct injection more so.

I would argue for some sort of goodwill from them.
I doubt the cats are bad.
Does it pass your MOT inspection? (If they do a sniffer test).
It's easy to tell if the call works, put a exh gas analyzer in front and back and compare readings. They can also pull the sensors and use a vacuum gauge to see it it pluugged. They should do that rather than replacing everything.

Just to update, once the rear O2 sensor was replaced the sequential test completed successfully and no other parts needed replacing. I have the extended warranty which covered the two O2 sensors and the final bill came to slightly less than the cost of the Cat. They didn't charge me for any labour or for the cost of removing the snapped studs in the exhaust manifold. It was a fair amount less than I was expecting so I'm quite happy about that. The car is back and does seem to be running better than before and I think the mpg is also better although it's only been a few days so can't be certain.

The car did pass the MOT (last December) but the only way they could get the correct lambda was to rev the guts out of it. The CEL was on at the time but they passed it anyway since the car was going in to Audi the following day to be looked at.

From what I can tell the cat warranty in the UK is the same as in the US but since the car is more than 8 yrs old the cat wasn't covered.

Did you refill your car with race fuel or octane booster?
Common problem in cats and lambda sensors.

I've only ever used Shell's premium unleaded petrol (V-Power at the moment). Ive never used anything else or any additives either.

Thanks for the update
My guess is the cat was good but the faulty sensor wasn't working
Since they did not have a sensor they replace the cat
They should have waited for the sensor
If it passed an MOT emission test the cat was likely ok

As long as you're good with the resolution that's all that matters