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Is this just a coincidence? I installed an Attack Blue Air Filter. Took the car to the track. Coming home I noticed a check engine light, not sure how long it had been on.
I have a BT OBDII code reader. The code reads as: "Chassis Control Module 1 requested Mil illumination P26C8."
So what does this mean, and could it be because of the new high flow air filter?
Brief search brings up stuff about the AFM (cylinder deactivation), which seems completely unrelated.
Is this just a coincidence? I installed an Attack Blue Air Filter. Took the car to the track. Coming home I noticed a check engine light, not sure how long it had been on.
I have a BT OBDII code reader. The code reads as: "Chassis Control Module 1 requested Mil illumination P26C8."
So what does this mean, and could it be because of the new high flow air filter?
Brief search brings up stuff about the AFM (cylinder deactivation), which seems completely unrelated.
DTC P26C8
Chassis Control Module Requested MIL Illumination
Circuit/System Description The chassis control module constantly monitors the chassis control system for any condition which
may adversely affect vehicle emissions. If a condition is detected, the chassis control module sets a
DTC and sends a serial data message to the engine control module (ECM). The ECM sets DTC
P26C8 to inform the technician that the chassis control module has set the emission related DTC.
The serial data message sent by the chassis control module also contains a request for the ECM to
illuminate the malfunction indicator lamp (MIL).
The technician can observe the DTC that was set by the chassis control module by reviewing the
ECM Freeze Frame records on the scan tool. The ECM Freeze Frame records also contain the
engine operating conditions present when the chassis control module DTC set.
Conditions for Running the DTC
The ignition is ON or the engine is running for greater than 3 s.
Conditions for Setting the DTC
The ECM receives a serial data message from the chassis control module indicating that an emission
related DTC has set in the chassis control module.
Action Taken When the DTC Sets
DTC P26C8 is a Type A DTC.
DTC P26C8 will continue to be current or active as long as the chassis control module is
requesting MIL illumination.
Conditions for Clearing the DTC
DTC P26C8 is a Type A DTC.
Diagnostic Aids
Communication codes, U-codes, as well as powertrain codes, P-codes, set in the chassis control
module will cause the chassis control module to request DTC P26C8 to be set in the ECM.
Reference Information
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
1. Verify there are no engine control or communication DTCs set.
If a DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
If a DTC is not set
2. Verify there are no chassis control module DTCs set.
If a DTC is set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
If a DTC is not set
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the
vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
4. Verify the DTC does not set.
If the DTC sets
Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
If the DTC does not set
5. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
DTC P3400
Diagnostic Instructions
NOTE: Do not replace the engine control module for this DTC. DTC P26C8 is
an informational DTC.
Correct any engine control and communication DTCs before
diagnosing chassis control module DTCs.
Here is a picture from the page in the Service Manual.
It is an informational code that says an emission related fault was detected somewhere. A fault in AFM is probably not an emission related fault.
Bill
Leaving the track I got the same code. I ran my last session using the fuel offered at the track, 98 octane I assume no ethanol. Could this fuel be causing an emission code? I’ve got about a 1/4 left. Curious to see if it goes away after running normal 93 for a while....
Yes it is an info code and it is permanent and is set when AFM valves fail. no it isn't emissions so make no sense.
you can either fix the AFM or tune it out with a tune HP tuners will Handke both disabling the AMF valves and turning off that DTCThanks FYREANT,
This process worked exactly as posted with the new HPtuners MPVI2. If you have a windows compatible laptop you can download the VCM suite for free directly from the website. As stated above, you only need to download, modify and burn the C304 CCM and will require 2 universal credits. Tuning with the MPVI2 now uses universal credits and is much more user friendly than the previous version. When you buy the MPVI2 directly from HPtuners, it comes with zero credits. You have to buy them separately. Check it out at their website. You can get the unit with credits from Amazon. Not sure how that works though. I chose to buy directly from the HPtuners website with zero credits.
After downloading the CCM file from my Vette, I modified it as shown above. I wanted to try and burn it with no credits. The VCM suite will tell you how many credits you need and then you can buy them at that point. After purchasing the credits you will have to resync your tuner and then the credits will show up in the VCM suite software. There are plenty of YouTube videos showing this process. Once the credits show up, you are cleared to burn your updated file. That's it.
The MPVI2 costs $299, 2 credits cost $99.98 and it literally takes no more than 30 minutes to download the current tune file, modify it and then burn it. Your laptop needs to be hooked up to the internet or the tuner won't be able to verify registration during the download or upload process. It verifies registration with the hptuners website each time you try these actions. At least that is what I experienced. The Vette side of my garage has great WIFI coverage, but the Camaro side has poor coverage and the software wouldn't download my Camaro tune file until I moved the computer outside of the car.
One word of caution, it takes approximately 5 minutes to download or upload the file and is a very high draw on your car battery. I highly recommend having a battery charger or tender hooked up to your battery during the process.
To answer a few of the questions asked about this, here is what I found:
1. The check engine light is now out.
2. No more clicking when the AFM valve motors try to open/close (I pulled the #32 fuse)
3. ECO, Tour and Sport all work as before.
4. 4 cylinder mode also works as before. I don't notice any difference with the exhaust sound when the car switches between 4 and 8 cylinder modes even though the AFM valve stays open all the time now.
5. The NPP valves continue to change the sound as before.
AFM Delete
To do this you will need:
HP Tuners with VCM Suite UPDATED TO VERSION 3.6 and two additional credits
NOTE: The credits needed for this are IN ADDITION to the credits used to tune the ECM. This means that your C7 will use a grand total of 4 HPT credits, two for your engine tune, and 2 for the FSCM tune!
Taken from the HPT forum:
As of Software version 3.6 you can now tune the FSCM/C304 modules however they do cost additional credits in order to license these modules which you will notice once you attempt to flash them. If you have no plans to tune/modify either of these modules then when you start the read process simply select DO NOT READ on the modules you have no plans to modify, this way the software will not ask you to license them. Keep in mind these modules cannot be read via the bus so a stock file is generated for you(you will see a popup that will state this clearly as well).
•1 credit each for FSCM A-F
•2 credits each for C304(C7 Corvette)
To clarify, I am referring to the valves circled in RED in the below picture. We are NOT talking about the valves circled in Green! The valves circled in RED are the AFM valves and are related to Displacement on Demand / Active Fuel Management for “Eco mode”. They serve no other purpose, which is why the Z06 does not have these valves since it does not have Eco mode.
In order to remove these valves from the exhaust, you will need to be able to stop the computer from thinking there is a problem by turning off the codes it throws. The main reason that we could not do this previously is the codes that are generated to illuminate the check engine light (CEL) when these valves are disconnected is not located in the ECM, but rather the FSCM. The same result happens when pulling fuse #32 under the hood as this also disables the AFM but the computer trips out as it thinks there is a problem. The FSCM module handles these codes which is also known as the C304 module.
For testing this, I pulled fuse #32 from the under hood fuse box and after two engine startup cycles received these 6 codes:
The first code is a master code, and the other 5 are individual codes. P26C8 will not throw unless something else throws first. So what are these codes for? Let’s look in the manual. First the P26C8 code indicates this: “Chassis Control Module Requested MIL Illumination”. Again, like I said this is a master code. When the other 5 codes came up, it triggered P26C8 which is the actual code that turns on the check engine light. What do the other codes mean? Lets look:
As you can see, they ALL relate to “Cylinder Deactivation Exhaust Flow Valves” which are the AFM valves in question.
Cool. So all I need to do is turn off the code for P26C8 then right? Whoa there killer… way wrong answer!!
If you turn off P26C8 from working, then you will not get notified for ANY other alert that the C304 module controls! The correct way to do this is to disable all the “Cylinder Deactivation Exhaust Flow Valve” codes individually and leave the P26C8 code fully enabled! If you do the job right, none of the AFM valve codes will trigger P26C8 and you are good to go!
Ok so how do I fix this already?!?!
As mentioned earlier, you’ll need HP Tuners and the VCM Suite installed on your laptop. It MUST be updated to version 3.6 or later or you will not be able to get to the FSCM module to proceed.
Make sure you have the HPT module plugged into the OBDII port, turn the ignition on (do not start car though). Go to “Flash” and choose “Read Vehicle”.
You will see a window pop up. First choose “Gather Info”. After it has gathered info you will see a window that looks similar to the below one. Here you can see the E92 ECM which is the main computer and the C304 CCM which is the FSCM module we need to tune. Ensure that the drop down box is set to “Read Entire” for the C304 module and then click the “Read” button.
(NOTE: you do not need to read the ECM module unless you need to change settings related to the ECM tune)
Once the read is complete, it will bring you into the files it read. Here we need to go to the “System” button (number 1 in photo below), and then click the “DTC’s” tab (number 2 in photo below). Now you’ll need to locate the appropriate codes that we need to disable in the list. The codes numbers are those indicated by number 3 in photo below.
Next you will need to locate the codes we need to turn off. I’ll list them here for easy reference:
DTC P12E3: Cylinder Deactivation Exhaust Flow Valve Control Circuit Open
In the below screenshot, you will see how to turn them off. Uncheck the box next to “SES Enabled” for each of these codes and then if you click on the “Error Mode” to the right of the check box for each code you will see it is a drop down box. Here, choose “No Error Reported” for each of these codes.
When you are done with that, its time to write the tune file back to the car. Go to the “Flash” menu pulldown and then go to “Write Vehicle”. You will get presented with a box as shown below:
This box is indicating to you that two additional credits are necessary to tune this new module with HPT as I indicated at the beginning of the thread. Once you click “OK” you will be given another popup asking if you are sure you want to continue which you will need to also hit “OK” again on.
After this the tune file is written to the C304 module and you’re all done! You are now welcome to disconnect fuse #32, or disconnect the AFM valve wiring harness connector, or even change out the exhaust to a different one that does not have the AFM valves in it at all!
Thanks to TSloper for his help with this!
Hope this helps guys!
Thanks FYREANT,
This process worked exactly as posted with the new HPtuners MPVI2. If you have a windows compatible laptop you can download the VCM suite for free directly from the website. As stated above, you only need to download, modify and burn the C304 CCM and will require 2 universal credits. Tuning with the MPVI2 now uses universal credits and is much more user friendly than the previous version. When you buy the MPVI2 directly from HPtuners, it comes with zero credits. You have to buy them separately. Check it out at their website. You can get the unit with credits from Amazon. Not sure how that works though. I chose to buy directly from the HPtuners website with zero credits.
After downloading the CCM file from my Vette, I modified it as shown above. I wanted to try and burn it with no credits. The VCM suite will tell you how many credits you need and then you can buy them at that point. After purchasing the credits you will have to resync your tuner and then the credits will show up in the VCM suite software. There are plenty of YouTube videos showing this process. Once the credits show up, you are cleared to burn your updated file. That's it.
The MPVI2 costs $299, 2 credits cost $99.98 and it literally takes no more than 30 minutes to download the current tune file, modify it and then burn it. Your laptop needs to be hooked up to the internet or the tuner won't be able to verify registration during the download or upload process. It verifies registration with the hptuners website each time you try these actions. At least that is what I experienced. The Vette side of my garage has great WIFI coverage, but the Camaro side has poor coverage and the software wouldn't download my Camaro tune file until I moved the computer outside of the car.
One word of caution, it takes approximately 5 minutes to download or upload the file and is a very high draw on your car battery. I highly recommend having a battery charger or tender hooked up to your battery during the process.
To answer a few of the questions asked about this, here is what I found:
1. The check engine light is now out.
2. No more clicking when the AFM valve motors try to open/close (I pulled the #32 fuse)
3. ECO, Tour and Sport all work as before.
4. 4 cylinder mode also works as before. I don't notice any difference with the exhaust sound when the car switches between 4 and 8 cylinder modes even though the AFM valve stays open all the time now.
5. The NPP valves continue to change the sound as before.
AFM Delete
To do this you will need:
HP Tuners with VCM Suite UPDATED TO VERSION 3.6 and two additional credits
NOTE: The credits needed for this are IN ADDITION to the credits used to tune the ECM. This means that your C7 will use a grand total of 4 HPT credits, two for your engine tune, and 2 for the FSCM tune!
Taken from the HPT forum:
As of Software version 3.6 you can now tune the FSCM/C304 modules however they do cost additional credits in order to license these modules which you will notice once you attempt to flash them. If you have no plans to tune/modify either of these modules then when you start the read process simply select DO NOT READ on the modules you have no plans to modify, this way the software will not ask you to license them. Keep in mind these modules cannot be read via the bus so a stock file is generated for you(you will see a popup that will state this clearly as well).
•1 credit each for FSCM A-F
•2 credits each for C304(C7 Corvette)
To clarify, I am referring to the valves circled in RED in the below picture. We are NOT talking about the valves circled in Green! The valves circled in RED are the AFM valves and are related to Displacement on Demand / Active Fuel Management for “Eco mode”. They serve no other purpose, which is why the Z06 does not have these valves since it does not have Eco mode.
In order to remove these valves from the exhaust, you will need to be able to stop the computer from thinking there is a problem by turning off the codes it throws. The main reason that we could not do this previously is the codes that are generated to illuminate the check engine light (CEL) when these valves are disconnected is not located in the ECM, but rather the FSCM. The same result happens when pulling fuse #32 under the hood as this also disables the AFM but the computer trips out as it thinks there is a problem. The FSCM module handles these codes which is also known as the C304 module.
For testing this, I pulled fuse #32 from the under hood fuse box and after two engine startup cycles received these 6 codes:
The first code is a master code, and the other 5 are individual codes. P26C8 will not throw unless something else throws first. So what are these codes for? Let’s look in the manual. First the P26C8 code indicates this: “Chassis Control Module Requested MIL Illumination”. Again, like I said this is a master code. When the other 5 codes came up, it triggered P26C8 which is the actual code that turns on the check engine light. What do the other codes mean? Lets look:
As you can see, they ALL relate to “Cylinder Deactivation Exhaust Flow Valves” which are the AFM valves in question.
Cool. So all I need to do is turn off the code for P26C8 then right? Whoa there killer… way wrong answer!!
If you turn off P26C8 from working, then you will not get notified for ANY other alert that the C304 module controls! The correct way to do this is to disable all the “Cylinder Deactivation Exhaust Flow Valve” codes individually and leave the P26C8 code fully enabled! If you do the job right, none of the AFM valve codes will trigger P26C8 and you are good to go!
Ok so how do I fix this already?!?!
As mentioned earlier, you’ll need HP Tuners and the VCM Suite installed on your laptop. It MUST be updated to version 3.6 or later or you will not be able to get to the FSCM module to proceed.
Make sure you have the HPT module plugged into the OBDII port, turn the ignition on (do not start car though). Go to “Flash” and choose “Read Vehicle”.
You will see a window pop up. First choose “Gather Info”. After it has gathered info you will see a window that looks similar to the below one. Here you can see the E92 ECM which is the main computer and the C304 CCM which is the FSCM module we need to tune. Ensure that the drop down box is set to “Read Entire” for the C304 module and then click the “Read” button.
(NOTE: you do not need to read the ECM module unless you need to change settings related to the ECM tune)
Once the read is complete, it will bring you into the files it read. Here we need to go to the “System” button (number 1 in photo below), and then click the “DTC’s” tab (number 2 in photo below). Now you’ll need to locate the appropriate codes that we need to disable in the list. The codes numbers are those indicated by number 3 in photo below.
Next you will need to locate the codes we need to turn off. I’ll list them here for easy reference:
DTC P12E3: Cylinder Deactivation Exhaust Flow Valve Control Circuit Open
In the below screenshot, you will see how to turn them off. Uncheck the box next to “SES Enabled” for each of these codes and then if you click on the “Error Mode” to the right of the check box for each code you will see it is a drop down box. Here, choose “No Error Reported” for each of these codes.
When you are done with that, its time to write the tune file back to the car. Go to the “Flash” menu pulldown and then go to “Write Vehicle”. You will get presented with a box as shown below:
This box is indicating to you that two additional credits are necessary to tune this new module with HPT as I indicated at the beginning of the thread. Once you click “OK” you will be given another popup asking if you are sure you want to continue which you will need to also hit “OK” again on.
After this the tune file is written to the C304 module and you’re all done! You are now welcome to disconnect fuse #32, or disconnect the AFM valve wiring harness connector, or even change out the exhaust to a different one that does not have the AFM valves in it at all!
09-03-2020, 08:44 PM
P26C8 Chassis Control Module Code
