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Discussion Starter · #1 ·
2023 Z51 with 1,300 miles threw code P12F0 - Cylinder Deactivation Exhaust Flow Valve Stuck Open-Bank 1. Dealer attempted to re-learn AFM actuator multiple times with no success and recommends replacement, but the part (#84896575) is nowhere to be found, now on special order with no ETA. Dealer says actuator is sluggish and doesn't open the valve fully (don't understand how they know that without dropping the exhaust...does anyone here know?). My concern is that without dropping the exhaust it might be a combination of the actuator, the linkage to the valve, or the valve itself. The linkage could be binding and need a little adjustment. If the valve is bad, I don't know if the valve is replaceable within the exhaust system...does anyone here know? I've looked at the exploded view, but can't figure it out. Could need more unavailable parts after torn apart to replace actuator. Dealer says it's OK to drive. It threw same code right after leaving. Do you guys agree? I would really appreciate any feedback on my situation. Many thanks in advance.
 

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I had the same P12F0 - Cylinder Deactivation Exhaust Flow Valve Stuck Open-Bank 1. I swapped the actuators from bank 1 to bank 2 and vise versa, the problem remains at bank 1 (Driver side) I also verified that the internal butterfly valves are moving freely when the actuators were removed and there was very smooth easy movement (verified internal movement with my Ferret Camera). I took it to the dealer and they sold me a bespoke alternator and a negative battery cable to the tune of $1200 and on the way home from the dealer the P12F0 - Cylinder Deactivation Exhaust Flow Valve Stuck Open-Bank 1 returned. I returned to the dealer and they did a diagnostic test and determined that I needed a new muffler, I told them they didn't know what they talking about. I now have a Range Technology RA003B AFM/DFM Disabler to eliminate the 4 cylinder mode. I now have error P12F1 Cylinder Deactivation Exhaust Flow Valve Position Not Learned (Bank1). I have had my check engine light illuminated for about 18 months. I plan on getting my volt meter and try to troubleshoot the circuit as the dealers don't know what they are doing. Good luck!
 

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Discussion Starter · #4 ·
I had the same P12F0 - Cylinder Deactivation Exhaust Flow Valve Stuck Open-Bank 1. I swapped the actuators from bank 1 to bank 2 and vise versa, the problem remains at bank 1 (Driver side) I also verified that the internal butterfly valves are moving freely when the actuators were removed and there was very smooth easy movement (verified internal movement with my Ferret Camera). I took it to the dealer and they sold me a bespoke alternator and a negative battery cable to the tune of $1200 and on the way home from the dealer the P12F0 - Cylinder Deactivation Exhaust Flow Valve Stuck Open-Bank 1 returned. I returned to the dealer and they did a diagnostic test and determined that I needed a new muffler, I told them they didn't know what they talking about. I now have a Range Technology RA003B AFM/DFM Disabler to eliminate the 4 cylinder mode. I now have error P12F1 Cylinder Deactivation Exhaust Flow Valve Position Not Learned (Bank1). I have had my check engine light illuminated for about 18 months. I plan on getting my volt meter and try to troubleshoot the circuit as the dealers don't know what they are doing. Good luck!
Thanks for your feedback. I'm waiting for the actuator to arrive and be installed by the dealer.
 

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The Range Disabler doesn't work on a C8, so that's irrelevant.

The actuators are external to the exhaust, and easy to inspect if you (or they) drop the bottom pan under the engine. It's also easy to disconnect the actuator from the valve and see if the valve moves freely. If it does, the the problem is most likely the actuator. The valve is a very simple design, and I think unlikely to fail if it worked properly in the beginning, but I don't think it's removable without replacing the muffler assembly.

Not 100% sure, but I don't think there's any linkage between the actuator and valve. I think the actuator works directly on the pivot of the valve. I agree that it's OK to drive. Might sound a little funny if the AFM valve is mostly closed, but won't hurt anything.

There a video that shows some of the inner workings, that might make this more clear. (There are also some factual errors in his description of the various modes, and the C7, but that doesn't affect how the valves actually work):

 

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Discussion Starter · #6 ·
The Range Disabler doesn't work on a C8, so that's irrelevant.

The actuators are external to the exhaust, and easy to inspect if you (or they) drop the bottom pan under the engine. It's also easy to disconnect the actuator from the valve and see if the valve moves freely. If it does, the the problem is most likely the actuator. The valve is a very simple design, and I think unlikely to fail if it worked properly in the beginning, but I don't think it's removable without replacing the muffler assembly.

Not 100% sure, but I don't think there's any linkage between the actuator and valve. I think the actuator works directly on the pivot of the valve. I agree that it's OK to drive. Might sound a little funny if the AFM valve is mostly closed, but won't hurt anything.

There a video that shows some of the inner workings, that might make this more clear. (There are also some factual errors in his description of the various modes, and the C7, but that doesn't affect how the valves actually work):

Thank you for the info regarding access and replacement. It's exactly what I was hoping for. There is a short linkage arm connected from actuator to the valve. And fingers crossed it's not a bad valve.
 
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