ECU/Tune Question: Can/Do they disable CELs

[Tom Sawyer]

Having recently going through a full ACE TC replacement + 75k service, there were a number of things exposed during the service that should have had a CEL indicator glowing. I was getting the TC code which I understand won't always throw a code early on, but I also had a number of broken vacuum lines some of which were to the secondary air pump. My mechanic was pretty amazed that it was not throwing a CEL.

In addition, he noted that when he first cranked it in testing, he did not have the MAF's connected and that should have immediately thrown a CEL... but it remained dark. For the record, I have run a full test with vagcom on instrumentation and the light definitely works.

From day one (my day one with the car of course), it has thrown the ECU Checksum error, MIL on (I've posted the actual code in an earlier post this year) and the consensus was that it is a pretty good indication of a tune (good, bad or otherwise).

That said, is it possible the 'tune' has totally disabled the setting of a CEL for any condition? Anyone ever heard of that? If so then I want to summarily dump this tune, whatever it is, and go back to stock even.... I know the first CEL I get I may have a doh moment, but I would rather know something is wrong. My shop also sells a Unitronic tune, haven't been able to find much about that tune here.

FWIW, I'm pretty anal about scanning the car esp with the TC situation, and I have very few codes, (the ecu code, a code for the right motor mount, a radio code for telematics module missing, and implausible signal on the trans temp sensor (wiring harness to be replaced)) but figured I'd throw this question out there.

TIA!

[alrightroad]

Normally tuners will target specific codes with their tune... O2 sensors, EGT sensors, SAI system, etc. and block those CEL's. I've never seen any mention of a tune on any Audi platform which blocked all CEL's. I'm sure some creative minds out there could do this in code but I seriously doubt any of the mainstream tune vendors would do offer this for fear of backlash by customers.

[Aronis]

It's sometimes odd. My TC was not locking, but I never got a CEL, just caught it by random VAG-COM scan, which I now do monthly. The dam thing was not locking and needed replacement for an unknown length of time. This was a big issue as the dam TC can fail without a CEL and thus ruin your transmission without a warning.

The CEL would come on for a small emission leak, (aka loose gas cap) when the car was newer, but that CEL never comes on any more and I catch the Small Emissions leak only when I randomly scan with VAG-COM.

So your issue does not surprise me.

Mike

[Tom Sawyer]

As always, greatly appreciate your thoughts on this. What you have said makes a lot of sense. I feel the tune I have is an issue at the very least since it is causing the ECU Checksum error. Once I have it in the shop to shore up a couple left overs from the TC swap I'll have them do a full scan, should be at least able to determine if it does have a tune. The unitronic tune is not terribly expensive, but I'm reluctant to go for that one just based on not seeing a lot of feedback here about their RS 6 tune. Anyway... again, appreciate the thoughts on this; I may have to try loosening the gas cap just to see what happens but my guess is I'll see no CEL.

[lswing]

I've never seen anyone on here with a unitronic tune....try Revo, Eurocharged, or APR. Good luck there!

[Tom Sawyer]

Yea, just not enough info about the unitronic to feel comfortable with it. Unfortunately, no shops around here that I know of for Revo or Eurocharged.

Interesting...

Eurocharge Software and Programmer (http://www.eurocharged.com/index.php?option=com_virtuemart&page=shop.browse&category_id=33&Itemid=99)

[hahnmgh63]

I'm currently running Revo but since I've removed the Cats (Milltek Catless Downpipes) and SAI system, I am getting a Custom Eurocharged tune that codes out the Secondary O2's (also available from Revo...Stage2) and the SAI system (not available from Revo). I am getting the programmer, actually getting a package deal of two programmers and two tunes. Custom RS6 tune and Custom Cayenne Turbo S tune (suppose to go from 520bhp+ to around 580~600bhp and TQ from 539 to600 ft/lbs (I've already got a IPD intake and Fabspeed Secondary cat removal straight pipes).

[Justin9212]

We do custom tuning here at my shop. The Checksum is the last step done after writing a new file to an ecu. Whomever tuned your car last did not do the final step after flashing. If you were closer to me I would do it for free. It takes about 5min to do. Most cars wont run at all without the checksum performed.

[Tom Sawyer]

We do custom tuning here at my shop. The Checksum is the last step done after writing a new file to an ecu. Whomever tuned your car last did not do the final step after flashing. If you were closer to me I would do it for free. It takes about 5min to do. Most cars wont run at all without the checksum performed.

Wish I was closer too, I would appreciate that! I'll check with my shop here and see if he can determine what the tune is and then I can decide if I want to stick with it if he can load the checksum or just go back to stock.

[Justin9212]

If you mailed me your ECU we could fix it that way too. Would just cost shipping.

[Tom Sawyer]

If you mailed me your ECU we could fix it that way too. Would just cost shipping.

Thanks, very cool of you to offer that! I'll see what the shop here can do regarding the checksum. If no luck there and I can work out some downtime for the car I'll reach out to you on it.

[Tom Sawyer]

Got her back today, after a scan with his Unitronic setup, it came back that the code looked stock. So... I guess it's possible it is either not reporting back correctly and I have an old or bad/incomplete flash or my ECU truly has an issue. Not having been in any other RS6's (stock or otherwise), I have no baseline. May be time to do some logging with the VAGCOM to see where my requested and actual boost hits. Regardless, I'm somewhat concerned about the code, especially if it is indeed keeping me from seeing CEL's. I suppose I could take it to the dealer and ask to flash it (correctly) to stock, but I wouldn't be surprised if they charged me more than what I can buy a Eurocharge tune and a hand programmer for!!

At least my Transmission is code free, that is indeed a beautiful thing!