YZF

Hi All,

My NPP dual mode exhaust started acting up this spring, and would intermittently open the values when the proper RPM/Throttle activated it.

Now, the valves are open when car is off, close when car is on, and do not open when RPM/Throttle should open them. I did remove the fuse, the valves remained open when car was on, sounded great!

When I replaced the fuse, the valves close when the car is turned on and do not open. A shop looked at the solenoid and they stated it was good. I have come across a couple threads where the OP has the same symptoms, they must forget to post what the fix was.

Summary:
Getting power to Solenoid, appears to be properly functioning (power to it valves are closed, fuse pulled valves are open)
Valves open/close depending on power to solenoid
Valves are not opening when RPM/Throttle inputs are sufficient
Question appears to be "what is not cutting power to the solenoid when parameters are met"?
Also, what is this Exhaust Flow Control Module I see talked about?

Appreciate all the help with contributors thus far and any that the experts can spare here!

4SUMERZ

The control module is located in the right side rear compartment behind the wheel well. Could be as simple as a connector issue.
It's a fairly simple wiring schematic.

YZF

Thank You, 4SUMERZ! I took a look at the wires at the exhaust flow control module, all look good. On to the next thoughts.

What is the failure rate of the module, I have not seen anything on the forum of this being a big issue. Any thoughts out there or opinions as to this being a module, wiring or other issue? Can it be from the computer itself not sending the data via that tan wire? if a connector issue, how to properly check that as it looks like all wires are in good shape. how can I check that the tan wire is good?

Car is a 2008, 37K, all stock.

4SUMERZ

When the fuse is installed, when you first start the car, is it loud, then goes quiet directly when started.
That is how it should work if all is Ok with the system. You say it will not open ever, unless you pull the fuse. That shows that the solenoid is working Ok.
It could be a glitch in the system. Try disconnecting the battery. This may reset the system. You will have to reindex the windows after you re connect the battery.
Here is a link with good information that might steer you in the right direction to solve your issue.
https://www.corvetteforum.com/forums...y-ideas-2.html

Dano523

On the factory NPP system, controller will only open the muffler gates at 3K RPM and above, and only when the gas pedal is depressed 60% or more downward.

If factory NPP controller is in play that as stated, disconnect the battery for 15 mins to allow the all the systems to hard reset when the battery is reconnected. if you still have problems, check the serial 2 bus (not the high speed main lan bus) that the NPP controller is getting it information to work from. Since the gates are closing once you start the car, then NPP is getting power to energize the vacuum solenoid to open it, and allow the vacuum from the intake manifold to reach the muffler gates.

Now having stated how the factory NPP controller works, the car may not have come with factory NPP, but instead have an aftermarket NPP in a box system instead. On these systems, no interconnect on the serial 2 bus system, so only controls if the muffler gates are open or not via basic switching.

YZF

Many Thanks 4SUMERZ and Dano523! I will try these recommendations out.

The NPP system is all stock, worked perfectly last summer and started acting up sporadicallly this summer.

When car is off, the valves do open, when fuse is pulled the valves remain open. Just does not seem to not be cutting power to the solenoid when the NPP system requirements for RPM and throttle are there.

FatsWaller

Here's a good write up of how It works and the modules in play. https://www.corvetteforum.com/forums...e-08-work.html
The part that fails most often is the vacuum solenoid which ends up stuck either open or closed. From your good diagnostics your solenoid seems OK.

4SUMERZ

Thanks, but Dano is the Sensei when it comes to the C6 Corvette systems, how they work, and troubleshooting them. I can somewhat manage to manuever the internet searches, and most time find the info that Dano has humbly shared with many a member on this forum. He has saved and helped many on here including yours truly.
Thanks Dano.

Dano523

System over all sounds like it working correctly power wise, and its just the class 2 signal to the NPP controller from the ECM/BCM that sounds like the problem.



The J206 splice bock is in the passenger foot well area just left of the bose amp location, while the J205 splice block is to the left of the IPC and just below in the dash.