mewalker2

Recently I started having issues where the bi-mode exhaust would not close on my '09Z. I have a M2W switch installed and noticed that sometimes it would not close when I pressed the button, but other times it would work with no issue. One day it completely stopped working and I was unable to close the exhaust.

Testing

I replaced the 10A fuse in the passenger floorboard where I had the M2W box installed. I started the car and the exhaust was still open so I knew the M2W was good.

My next thought was a vacuum leak. I've seen many posts with people finding cracked lines near the brake booster so I checked there and found no visible cracks.

I bought a MityVac MV8000 from O'Reilly's to test the vacuum. (Ignore the Very Sexy in the photo)



You can test vacuum at a few different locations. I chose to test at the rear of the car where the line runs to the exhaust solenoid behind the passenger taillights, just to eliminate that entire vacuum line to the intake manifold. You access the solenoid by removing the passenger tail lights. I removed both lights so I could use both hands. The picture below shows the cover that is over the solenoid. Remove the harness clip on the left side and pull up on the cover to twist it out of the way.





Solenoid cover removed:




I went ahead and removed both lines from the solenoid and un-clipped it from the harness, for removal. The line that comes up from the bottom of the car to the top of the solenoid is where I tested with the MityVac. It runs to the vacuum tank reservoir then to the firewall and up to the back of the intake manifold. I attached the proper fitting to the MityVac and stuck it into the line. I pumped it up and the gauge did not move. No vacuum leak to the manifold! I then tested the other line that runs to the solenoid. This one goes to the actuators on the mufflers. I pumped it up and the mufflers closed and gauge didn't move. No leak to the actuators on mufflers! This eliminated the vacuum lines as being faulty.






I knew then it had to be the solenoid (#27 in diagram) or the control module (#21 in diagram).




You can ensure that the solenoid is getting power by checking the volts from the control module. FYI, the module is mounted on the passenger side of rear fender well. You can pull the carpet back to see it.




Start the car and test the harness with a multi-meter where it attaches to the solenoid. It should be 14 volts. If you do not get 14v, then the control module may be the issue (# 21 on diagram), or something electrical further upstream. (Make sure you have the 10A fuse installed in the passenger floorboard)




The way I understand it, the control module sends 14v to the solenoid until the car reaches 3500RPM (keeping the baffles closed). When it hits 3500RPM, the control module kills power to the solenoid (allowing the baffles to open). If you have 14v on the harness then the solenoid is more than likely the issue and should be replaced. GM part 25794610 $65 at dealer. This part number is ONLY the solenoid.



In my case, the harness was testing at 14v so I replaced the solenoid. For testing purposes, I fired it up with the 10A fuse installed (instead of M2W) and all was quiet again! Easy fix this time!!


Please add details or any other helpful tips for future use by other members. This forum has a wealth of knowledge and has helped me many times.

Brian71

Your write up was excellent. The solenoid in my car was acting up but not all the time. Today it wouldn't close the flapper valve on the mufflers.
I left the car running while I got access to the valve to check for power. Once I had 14 volts I checked for vacuum.
I have a solenoid on order from the dealer.
Thanks again.

phipp85

Great post. Thanks for the info.

mewalker2

Thanks gentleman, glad the post was helpful.

MTPZ06

Its the one I'll certainly refer to if I ever need to do this.

LMB-Z

Nice write-up. Congrats on finding and fixing the problem. I replaced mine right after I bought the car. Took a couple of hours to diagnose and about 20 minutes to fix.

flyint

Thanks for the excellent info. I recently had the problem manifest itself while on a drive. The exhaust tone just changed for no reason. Did a little trouble shooting with the help of friends here on the forum. The fuse for the exhaust was blown...the one in the fuse box under the pax side floor board. Replaced the fuse and it blew again. Not having any test equipment, I went to the Chevy dealer and thru their diagnostics discovered that the culprit was this solenoid that you have written about. Ordered new part and will put it in on Monday.

TEXHAWK0

My friend's car was blowing fuses.
If your car is blowing the fuse, you obviously cannot check the voltage until you get the solenoid out of the circuit, but a quick check might be to disconnect the solenoid and see if the fuse still blows. If it does not, then the solenoid is probably the cause. With the solenoid out of the circuit, you can check the output of the control module. (14V)

I just replaced this solenoid on a friend's car, and failed to notice that the solenoid just clips onto the bracket, so you do not actually have to remove the bracket. You can just fold the cover back and unclip the solenoid.
Just wanted to point that out so it might save someone a little work.

By the way, Mewalker2 did a great job on the original post.

Another note: The black dust cap over the vented end of the solenoid was missing on the new one, so I transferred it over.. However, the new solenoid did come with a new bracket.
The new solenoid should have the dust cover, but I guess the Chinese guy that adds those was sick the day mine was assembled.

TEXHAWK0

I had never heard of any solenoid failures until a friend had his exhaust stick open.... Looks like it is more common than I thought, so bump to the top...

mewalker2

Thanks for the additional details TEXHAWK! Strange that your new solenoid did not have the round cap on the end, as mine was complete.

rhinonm

I used this thread to replace mine...06 with 20k miles.

TEXHAWK0

It should have been complete, but I guess the Chinese guy that puts the dust caps on was sick the day they assembled my solenoid. Just my luck.

pewter50vette

great write up, this will save some of us a trip to the stealer ship later.

Tripleblack51

I wanted to thank mewalker2 for taking the time to put up this post/great write up with pics.
I just replaced my exhaust Solenoid using your write up.
It was fairly straight forward with the pictures and I saved myself a trip to the dealer along with a few bucks!
People like you are what makes this site great!
Thank you.

mewalker2

Glad to hear this thread continues to help diagnose exhaust issues. Thanks for all of the input guys and good work finding your problem!

03worthy4link

Hate to revive a thread, but this shouldn't be so bad since it isn't that old lol.

My exhaust valves will not open. They're stuck closed. Even with the fuse pulled they stay closed and always quiet. anyone ever had a solenoid crap out and stay closed, not open?

mewalker2

Have you double checked that you're pulling the correct fuse? After verifying the fuse, try pulling the vacuum lines off of each actuator on the mufflers and see if they open, just to ensure they are not seized somehow. You could also try testing the control module for 14v (while car is running), then pull the fuse, then test control module again to be sure you have no voltage. If that checks out then maybe try replacing the solenoid if you're willing to throw $65 at it just to rule it out. Let me know what you find.

TEXHAWK0

The valves should be open with no vacuum.
If closed with the car off, seems to me they must be stuck.

lane_change

Working to diagnose this same stuck closed issue with a friends ZR1.

Car off - Flaps are open
Car on - Flaps are closed (has vacuum). If I pull the line off the solenoid, they open. If I pull the line off the engine bay, they open. If I keep all the lines plugged in properly and pull the 10A exhaust module fuse, they stay closed. If we go above 3500rpm, they stay closed.

I pulled the solenoid out, it seems okay...going to check the voltage to the solenoid, but it seems this issue is 100% opposite of most issues people are experiencing. Anyone have any clue where we should be looking?

mewalker2

What were the results on the control module voltage test? There's been a couple folks now with the same issue of the valves staying closed even with the 10A fuse pulled.