RossD Reader
July 28, 2009 8:44 a.m.

I think I've figured out my own Check Engine Light coming on and off seemingly at random. I did have it check and my indy Audi mech, and he said there was nothing wrong with my O2 sensor or the cats. The CEL stayed off for a while and I realized I was only going to BP gas stations. I was also only getting the highest octane available and it didnt have ethanol in it. I am not sure if its BP gas or if its the lack of ethanol or the combination but since I've been staying away from MotoMart gas stations and sticking to BP and non-ethanol high octane gasoline the CEL hasn't come back yet. Anyone else notice this at all? Any other crappy gas stations or any other good gas stations? (This is for my '00 Audi A6 2.7T Quattro.)

Rusty_Rabbit84 HalfDork
July 28, 2009 8:51 a.m.

what codes is it thowing on?

Paul_VR6 Reader
July 28, 2009 9:05 a.m.

2.7t's throw cels for a small cross breeze. Scan it, but don't be surprised when it comes back with all sorts of random stuff that doesn't make sense. I had a similar situation with by B5 S4 which started like this (random cel for misfires) and it eventually turned into a larger problem (massive misfires) that was one of the ignition modules going bad.

RossD Reader
July 28, 2009 10:15 a.m.

I believe it was the O2 sensor(s), but my mech said that the O2 and cats were fine when he tested it and just cleared it for me. Then it came and went seemingly at random. It was off for weeks until I went to MotoMart for some gas and it came back on. I noticed that I was only going to BP gas stations so I've stopped going anywhere else and it hasnt been back since (another couple of weeks). Maybe the ethanol or crappy gas mixed with good gas would throw a code at the O2 sensors and would trip and clear when the crap would be under a certain mixture with the good gas. Just seeing if anyone else noticed this happening too?

Paul_VR6 Reader
July 28, 2009 10:17 a.m.

You'll get O2 bank efficiency codes until the misfires are bad enough to cause a cel. Never had it happen with different kinds of gas, but entirely possible. You can check it with a vag-com watching the blocks for misfires and see if its all banks or just one.

RossD Reader
July 28, 2009 11:32 a.m.

Thats some good to know info, thanks Paul.

Rusty_Rabbit84 HalfDork
July 28, 2009 11:36 a.m.

i have a stupid "Cat Effiency" code that keeps being thrown on, its the stupid Hi-Flo cat the last owner put on. I clear it out, hoping to drive atleast 1 drive cycle without the CEL popping back on, so i can get it smogged. No such luck. I even put an anti-fouling cap on it, like the caps for old V8 70's cars, trying to trick the o2 sensor... no such luck again...

RossD Reader
July 28, 2009 12:10 p.m.

Rabbit: Try running BP high octane w/out ethanol. That cat effiency code sounds fimilar. I cant remember for sure what the code was... Maybe it'll work...

m4ff3w Dork
July 28, 2009 12:11 p.m.

I thought a CEL was SOP for a VW?

Rusty_Rabbit84 HalfDork
July 28, 2009 12:30 p.m.

ya im thinking the cat is problem and i will need to get a stock one welded back on, unless my company could write some code to be flashed on my car to turn it off...

you could also get a VAG COM code reader for a laptop - like 5 bucks on ebay...

Paul_VR6 Reader
July 28, 2009 2:58 p.m.

Make sure you're not logging little misfires causing that code. It will throw that code first when the ignition amps are bad with the 3pin coils and when the coils are going with the 4pin ones.

You'll need to log in to post.

Also on Grassroots Motorsports

Follow Us to the Nürburgring

4 hours ago in News

Follow along as James Clay from BimmerWorld contests his first ADAC Zurich 24-Hour race at the Nürburgring.

You Need This: 2005 Lotus Elise

4 hours ago in News

A Lotus Elise looks so right in British Racing Green.

2017 Mazda MX-5 RF

6 hours ago in New Car Reviews

We're big fans of the Mazda MX-5. Now Mazda went and put a retractable fastback on their fourth-generation car. So, ...

From the GRM Vault: Test Driving BMW's E30 M3

9 hours ago in Articles

We tested BMW's E30-chassis M3 back in 1989. Here's what we thought.

Project Ramp Truck: Installing Sound Deadening

11 hours ago in Project Cars

Time to cut down on heat and road noise making its way into the cab.

Eric Foss Sets Fastest Time Ever at the Tire Rack Ultimate Track Car Challenge

1 day ago in News

47 of the country's fastest cars battled it out for track supremacy.

Who Wants to Design the Next GRM T-Shirt?

1 day ago in News

Blipshift is involved, so you know that it will be cool.

Reader's Ride of the Week: Improving Upon the Ultimate Driving Machine

1 day ago in News

This E36-chassis M3 just keeps getting better.

What Was the Most Powerful Car at the Grassroots Motorsports Dyno Day?

1 day ago in News

What if we told you it was an Audi?

Up to the Challenge

4 days ago in Articles

Torque: It's how Glen Bunch's vintage Dodge keeps pace with today's machines.

This Friday: The Ultimate Track Car Showdown

5 days ago in News

Come watch some of the country’s top track cars duke it out for fame, glory and some tasty prizes.

You Need This: Metallic Brown Toyota Celica

5 days ago in News

This looks a lot like one that we had in our fleet back in the day.


Grassroots Motorsports Magazine

Subscribe Today

Also get your instant access to the digital edition of Grassroots Motorsports Magazine!

Learn More