Agree….I think I’ll start a dialog with Borla in advance to see where that leads. Pretty sure I haven’t hit that million mile mark as of yet. But it’s the AFM, not the exhaust.

 

Yes, understood. And agree that is consistent with the code. All of the valves being discussed are part of the muffler system. The Cylinder Deactivation Exhaust Flow Control Valves (aka AFM valves) are at the inlet to the muffler system. The other two are the Tailpipe Exhaust Flow Control Valves (sometimes called the NPP valves), and are ....found at the tailpipe.

 

OK…spoke with Borla this morning (Ryan) and as far as fixing a stuck valve it is a complete replacement of the exhaust. Warranty will cover parts/labor…..but a replacement system could be weeks away, he couldn’t say. He did say that warranty replacements are served first however.

In giving him background on what I have done so far (relearn), he said he has never heard of a tool that can do the relearn other than the factory tool from GM. In speaking further, he did say there are tools out there that can flip the valves open/close, but not calibrate (relearn) as the GM tool has a wide tolerance as actuators/valves are like a box of chocolates (you never know what you’re going to get). He said it should go on the GM tool and that will decide the way forward.

So it shall be….

 

I have the same tool and it sure can do a relearn. Follow this youtube video to perform the relearn:


When you initiate the relearn you can actually see the actuators opening and closing the valves if you have someone in the car hitting the learn button and you are looking at the exhaust through the mesh of the rear bumper.

Being it's bank 2 it's the passenger side. I bet when you do the cylinder deactivation relearn you will see the passenger side afm valve stay open for way longer than the drivers side one. If the actuator arm was not adjusted to the proper length the valve might not open and close properly, triggering this issue. There are several other reasons why this issue might be triggered. But a replacement passenger side afm valve section would be the worst case solution.

 

Yes, that’s the video that I followed…..thanks for the response.

Borla is saying that this tool only opens and closes the valves and states whether the valves successfully (or not) met the calibration limits stored in the ECM…it does not adjust the limits and that only the GM tool can. I’ve had the ATAK installed for nearly 2 years (Dec 12, 2022) and about 6000 miles. When my dealer installed the system they did a relearn as part of the install. So I hopefully will find out what’s up next week.

 

Wonder what "adjusting the limits" means? What I thought happened in a learn process, and this is based entirely on my assumptions about how it works, is that the actuator would be opened to the point where the valve stopped, and closed to the point where the valve stopped, and then those two position are recorded. Once the recorded, then the when it opens or closes the valves normally, if it senses that the valve did not stop at those recorded points (either going further, or not as far) it would indicate a potential issue, by way of a DTC code. So, its not really "adjusting limites" so much as it is determining and recording the limits of the mechanical valve and then looking for departures from that during normal operation. But that is just what I thought.

Edit: Add from the Service Manuial, here is the "description" of the Cylinder Deactivation Exhaust Control Valve Learn Procedure: "This procedure triggers the control module to learn the values of the component: Q15 Exhaust Flow Control Valve"

 

From what I understand, there is a considerable tolerance in open and closed positions of the AFM valve. This valve is either fully open or closed (AFM active) as opposed to the NPP which has multiple settings in between fully open/closed but the learning process is to establish the fully open/closed limits of all the valves. It seems there is up to a 10% tolerance on both limits so between the actuator, linkage, and valve tolerances, there is plenty of error to support this tolerance (IMO). I hope this is the case for me as I really don’t want to go through the whole replacement process….but I may end up there.

 

The NPP valves, or the "tailpipe exhaust flow control valves on the C8 do not have multiple positions either, although the communication system PWM would support that. I have read that the Z06 does have multiple positions for that. But in the C8, they are either open, or closed (unless it was changed in later model years. Here is the description of those valves from the Service Manual. You will notice it referes only to open and closed position.

I do not disagree that there is going to be some tolerance in the open and closed positions. We must assume that the once the positioned are learned, then the system that detects an issue with the valves will include the tolerance in the algorithm. But, I also believe that detection of the out of range is sensitive. I say that because even if an actuator is simply removed, then remounted to the same muffler valve, its position may be disturbed enough that the learn procedure is required.

"Note:
You may notice an exhaust tone change due to the AFM system activation, or during certain driving conditions to meet Federal noise pass-by
regulations. Review the cylinder deactivation exhaust flow control system operational modes listed below for additional details.
1. Stealth Mode: Exhaust tailpipe valves will be closed at all times when the engine is running.
2. Tour Mode: Exhaust tailpipe valves are closed when the engine is idling and during normal/non-aggressive driving. Valves open during
aggressive driving.
3. Sport Mode: Exhaust tailpipe valves are open when the engine is idling and during most driving scenarios. See note above.
4. Track Mode: Exhaust tailpipe valves are open at all times. See note above."

 

Interesting….when I sit at idle and cycle between the modes I hear the valves moving, and with the exception of weather/tour, the other two modes (sport and track) have a different tone….beats me.

 

Sure. At idle, if I toggle between Tour and Sport, or Tour and Track, the valves will be closed in Tour, but open in both Sport and Track. I hear no difference in the tone between Sport and Track at idle. They are also closed in Weather Mode, or whenever the engine sound is set to Stealth. Mine is a 2021, and that Service Manual description is from essentially a 2020. What year do you have? And, do you have a Z06? Z06 is supposed to have variable position, and as I noted, the control is by pulse width modulation, so it is capable of conveying variable positions to the actuator.

I checked the part numbers for the exhaust valve actuator for my 2021, and also the 2024 Z06, and the part numbers are the same (84896575) and are said to fit 2021-2025. So that suggest to me that that the actuators are already capable of assuming variable positions (if the Z06 has that feature) if so commanded by the control signal. The part numbers are different for the 2020 model. I think that is because in 2020, while the Cylinder Deactivation Exhaust Control Valves included a feedback signal to the controller (which is the Fuel Pump Power Control Module), that feedback path is not shown in the schematics for the Tailpipe Exhaust Flow Control Valves. I think in 2021 and later years that path was added and the part number sere changed. I also read that in a post - but I wll not be able to find that again.

 

Mine’s a 2021 as well…..

 

OK…so the dealer has verified that AFM #1 is stuck open. They say the actuator and linkage is good. But the valve is stuck open….they asked if I only drive in track or Z mode as a buildup of soot could be caked up on the valve from not going into AFM. The answer to that is no….I drive in MyMode on the freeway and AFM is constantly being operated and up to a couple of weeks ago, no CEL.

So I’ve filed the paperwork with Borla for replacement…..let’s see how that goes and how far they go in standing behind a product that lasted about 6,000 miles.

 

Sorry to hear about that. Borla will take good care of you based on everything I have ever read about their service. Let us know.

 

Well…picked up the car earlier this morning, CEL still shining bright. Had a talk with Borla which was a zero info conversation in which I was told I should hear something today from higher up…..we will see.

But, had a long chat with the Corvette Master mechanic about the issue in which info not posted anywhere was shown to me regarding my very problem. I will post this info after my dialog with Borla concludes one way or the other…..it will raise eyebrows.

 

Borla contacted me this afternoon and asked for paperwork (which I provided) and stated that they will replace the entire system at their shop (local to me). This is a true testament to product support which I (coming from 40 years in Aerospace) totally agree with and appreciate. They will need to get a new system from the factory in Tennessee and schedule an install date, but it will be this year. I will still share what I have learned from GM after this is done to benefit those who don’t know what I now know.

The car is completely driveable and no discernible degradation in performance, etc. I probably won’t put 200 miles on it for the rest of the year as rain is on its way and destroys the value of a C8 (that’s humor BTW).