Hi All,

So about a month ago my 2001 S4 (currently at 76K miles) blew a Spark Control Unit - basically, one day the car started to idle super-roughly. It would literally shake pretty badly - but there was no Check Engine light at first. Next morning it came up on my way to work - which is roughly 10 miles. I read the code in the parking lot - Multiple Misfires.

I took the car into the Audi dealer ASAP - another 3 miles.

..So $993.00 later I picked my S4 and the Check Engine light came back on in about 15 minutes I drove out of the Dealership.

So I read the codes again - Malfunctioning Catalytic Converter OR EGT (Exhaust Gas Temp) Sensors.

Brought the car back immediately - they said it's my fault since I drove the car with the Multiple Misfires condition which caused damage to the Catalytic Converter. They estimate repairs at about $2000 - 2 EGT sensors ($550 pair) + Cat converter ($1000 - California car) + labor.

QUESTION: is there anything I can do myself to diagnose exactly what throws the error code? I checked with Shokan.com and they offer pre-owned EGT sensors with 6 months warranty for $125 each. But what if I replace them and it's not the issue, you know what I mean? Any good suggestions \ advice for my situation would be very welcome.

...I had a desperate thought of trading in my baby S4 and getting a brand new car - do a lease of some sort, but first - it'd be a heartbreak for me, and second I just simply do not want to get into payments right now..

So I would really appreciate some good advice on what I can do at this point MYSELF to resolve the issue - I mean I do not have $2000 to shell out to Audi dealer..

Thanks for reading..

 

That's what you get from the stealership...sorry man.

I didn't know misfires could damage the cat...you could get new downpipes altogether for that price, something like the VAST piggies if you're on a budget. EGT's are expensive so I would hold off on those until you're sure one or both are actually bad.

You could just drive around and pollute for the time being....

 

Hmmm.. Actually, a good point regarding the exhaust pipes upgrade - I actually can buy those in that $2000 ballpark - AND they come with cats.

...As about the EGT sensors - does it sound reasonable to invest $250 into a used pair? Even if they come with some warranty?

Also I heard (and I found a how-to) that EGT sensors are a bitch to replace labor wise..

 

They are not that bad to remove from the downpipes but the digital connectors are under the fuel rail on the intake mani. Not sure how much you have to remove to get at those connectors.

I wouldn't do anything until you can narrow down the cause of your CEL. Can you post the exact code number and description you got?

 

Thanks - I'm trying to contact the dealership right now to get exact codes and their problem description.

More info to come - ty for your help!

 

New guy here, but I've been around the block a few times with cars. To own a car of this caliber and price on a budget, you are going to need to find an indie you trust or preferably learn to do some work yourself. Dealers work on commission, both the parts they sell and the labor they perform lines their pockets. They like to replace everything they think you will pay for, troubleshooting is dead for all intents at most dealers. Go get the codes pulled by a friend or Autozone/Advance, etc.

 

Hey All,

So I read the CEL code last night - P0431 - looks like it's referring to the driver-side cat.

I erased the code yesterday but the CEL came back on this AM on the way to work.

Any ideas how I can find out what went bad?

Thanks!

KK

 

...I'm researching online the P0431 code details - i found some references to a Audi Tech Bulletin regarding re-flashing the ECU software to get that code cleared? Anyone have comment on that - does it pertain to 2.7t engine?

KK

 

..also found this reference:

>>> Secondary Air Pump running intermittently
I changed the pre-cat O2 sensor which had started throwing the P0431 code. I have noticed since that the secondary air pump is not warming up the cat.

 

No idea, but it sounds like they are reflashing the ECU to delete the code - basically this means the computer is sent a hardcoded number that is always within range and the bad sensor is completely ignored (doesn't even have to be installed). This eliminates CELs but it does not mean the problem is fixed.