Over the last month I have had the check engine light come on, and used ross-tech VCDS to copy the codes and clear the light.


I have also noticed a substantial decrease in my gas mileage since then. is it related? But not sure where to start or what exactly it might be. Please help.

Here is the info VCDS gave me:

Control Module Part Number: 3B0 907 551 BA
Component and/or Version: 2.8L V6/5V G 0003
Software Coding: 07251
Work Shop Code: WSC 02325

16815 - Warm Up Catalyst; Bank 2: Efficiency Below Threshold
P0431 - 35-00 - -

16805 - Warm Up Catalyst; Bank 1: Efficiency Below Threshold
P0421 - 35-00 - -

17521 - Oxygen (Lambda) Sensor; B1 S1: Internal Resistance too High
P1113 - 35-10 - - - Intermittent



The Oxygen code only came up on the first time the light came on.

2000 A6

Thanks

 

IIRC B1 S1 stands for Bank 1 sensor 1. So it would be the pre-cat o2 sensor. If it is faulty it could be giving you two of the errors you are seeing. Cat problems are a pretty common problem on these cars. Mine were replaced at around 100k miles.

I would start with just replacing both pre-cat o2 sensors and see what happens. I'm sure they're original and could use replacing anyways. I read a long time ago that the dealer could reflash the computer to change the threshold for the cats.

FWIW, I have been getting the same o2 code as you for almost 3 years now, and knock on wood, but it's the only code I ever get. It has never set the CEL.

Get more opinions before proceeding.

 

Ok, that what I was thinking it was, but I am never sure about these emission codes.

The Cats were replaced at 85k a year ago when i bought the car. so hopefully its not them, well actually that would be better because they are under Warranty.

I plan on calling my mechanic today, but I wanted to get more opinions on it to. Thanks



PS. I have not really dug into VCDS since I got it, but is there a way to do Diagnostic on these codes any further with it?

 

When they replaced the converters, did they update the ECU? There is an update on the ECU which raised the O2 sensor reading threshold. Unfortunately, it is a dealer only procedure and can cost you around $350.

As for checking the O2 sensors, looky here...

https://www.audiforums.com/forum/sho...lock&page=2://

But in general, it sounds like you need your O2 sensors replaced. Mine followed the same symptoms. At 79K, both cats were replaced. After that the code P0421 came back at around 82K. They flashed the ECU with the update. At 105K, last week, P0130, P1113 and P0421 again. Replaced all 4 O2 sensors and she is running good again.

You can get all 4 sensors for about $600 total from Amazon. I got mine from the local shop and paid about $800. In either case, make sure to get pre-fitted Bosch sensors. Other sensors in Audi tend to not work

 

I am not sure about the ECU update. I will ask when I call my mechanic back later today.They put the cats on when i bought the car, but its not a dealer. Just a local guy, but seems to know what they are doing and have a very good rep. so we will see. He told me it sounds like cats, but wonders why since they just put them on, so he is doing some research for me.

I hope I don't need sensors just for the fact I don not have that kind of money right now.

Does anyone know if this would cause a decrease in gas mileage? That is one thing i have noticed, but could be the cold weather all of the sudden as well.

 

cold weather brings winter gas and can lower your mileage.
bad o2 sensors can lower your mileage.
bad cats can lower your mileage.

But most likely the bad o2 with winter gas.

 

I've had the check engine light with the 16805 and 16815 fault codes for a while. Both are Warm Up Catalyst: Bank 1 (or 2): Efficiency Below Threshold.

It seems that when I change the engine oil and turn off the check engine light with Vag-Com, I can drive 200 - 300 miles without the light coming back on. After that, after turning off the CEL it will come on already after about 100 miles.

Could the 16805 code be due to something else, and not the cat and sensors? Maybe the crancase recisrcultation system?

 

About a month or so ago i finally went to the dealer and had the ECU updated.. Took care of the problem and only cost me $248..

Yes for a guy to stand there and watch a computer do the work.

 

Due to the high cost of catalysts, it is a good idea to hook the car up now and then and do a readout on the sensors, maybe at service times. A long term fuel trim that is too rich can fry the catalysts. You can see this in the readouts and replace lazy O2 sensors and keep the catalysts happy a lot longer. By the way, try www.oxygensensors.com for the lowest price on OEM sensors.