NPP Failure
Thread Starter
Team Owner
Joined: Jul 2004
Posts: 40,338
Likes: 786
From: Redondo Beach, California
NPP Failure
My 08 NPP optioned car has failed into the muffler bypass mode. I originally had a "Mild to Wild" accessory on the car. It functioned properly for close to two and 1/2 years when it suddenly failed and I could no longer use the remote to transition between mufflers in and mufflers out of the exhaust circuit. I've removed the Mild to Wild accessory and restored the fuse configuration to stock. The car still runs with the mufflers out of the exhaust circuit.
Tips for how to start trouble shooting this? To replace the original 2 ten amp fuses, I've installed fuses with a LED red light that will light up if the fuse is blown. My new fuses indicate that they have not blown.
Without the mufflers, the car has a very annoying drone while freeway cruising. I'm out of the factory warranty period.
THANKS!!
Tips for how to start trouble shooting this? To replace the original 2 ten amp fuses, I've installed fuses with a LED red light that will light up if the fuse is blown. My new fuses indicate that they have not blown.
Without the mufflers, the car has a very annoying drone while freeway cruising. I'm out of the factory warranty period.
THANKS!!
Team Owner
Joined: Sep 2005
Posts: 20,352
Likes: 568
From: Ventura County, Calif
Elmer forgot to give you his vacuum troubleshooting guide: 
With the car running, pull off one line from an actuator and see if there is vacuum on the line. If there is, the actuator you took it off is "open" and leaking. If no vacuum on the line, plug it back and remove the other line from the other actuator. If you have vacuum, then the 2nd actuator is leaking. If you don't have vacuum, then the loss of vacuum is toward the engine.
Elmer
Elmer
Thread Starter
Team Owner
Joined: Jul 2004
Posts: 40,338
Likes: 786
From: Redondo Beach, California
The vacuum lines going to the vacuum/mechanical actuators are in tact. Also, both sides have failed. Some suggestions for actuator upstream vacuum checking?
I posted this problem, because if I have this problem, then I'm thinking others may have also.
I was interested to read the post where someone had a problem with their video screen going blank. I've had this problem also, on a couple of occasions. Turning the engine off and restarting has solved this problem for me. Now, I know that the real solution is to get a software reload! And the GM CD software reload disk part number was given.
Could my NPP problem be a computer problem? The mind boggles.
I posted this problem, because if I have this problem, then I'm thinking others may have also.
I was interested to read the post where someone had a problem with their video screen going blank. I've had this problem also, on a couple of occasions. Turning the engine off and restarting has solved this problem for me. Now, I know that the real solution is to get a software reload! And the GM CD software reload disk part number was given.
Could my NPP problem be a computer problem? The mind boggles.
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 25
From: Austin Texas
Intact lines don't mean much, you need to check if there is any engine vacuum in the lines. start at the actuators, then trace the vacuum lines back checking every junction to find where you are losing vacuum.
Moderator emeritus
Joined: Jun 2001
Posts: 18,599
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From: Jacksonville Florida BWO Dayton, Cincinnati, Bloomsbury NJ, Cincinnati
2015 C7 of the Year Finalist
No vacuum and the valves go open. That is why you get a brief loud noise on start up as the vacuum builds up to close the valves. If the valves stay open, no vacuum has gotten to the NPP. Put your finger over the end of the main run while the car is running. You should feel the vacuum at the hose. No suck, follow the line toward the engine until you find the crack or hole.
Elmer
Elmer
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Thread Starter
Team Owner
Joined: Jul 2004
Posts: 40,338
Likes: 786
From: Redondo Beach, California
I can jack the car up for sure. Will I be able to trace the vacuum lines forward to the front of the car, or will they disappear.
Question: Somewhere, there's a electromechanical vacuum solenoid valve that applies or removes vacuum to the NPP lines. So, I guess the question for now is, ...can someone please tell were this solenoid is? I'm just assuming that there's someone out there in radio land that knows the answer off the top of their head. I do have the thick three volume set of maintainance manuals, so I'll have a go with them tomorrow.
Thanks
Question: Somewhere, there's a electromechanical vacuum solenoid valve that applies or removes vacuum to the NPP lines. So, I guess the question for now is, ...can someone please tell were this solenoid is? I'm just assuming that there's someone out there in radio land that knows the answer off the top of their head. I do have the thick three volume set of maintainance manuals, so I'll have a go with them tomorrow.
Thanks
Race Director
Joined: Apr 2005
Posts: 10,436
Likes: 4
From: Everett Wa
I can jack the car up for sure. Will I be able to trace the vacuum lines forward to the front of the car, or will they disappear.
Question: Somewhere, there's a electromechanical vacuum solenoid valve that applies or removes vacuum to the NPP lines. So, I guess the question for now is, ...can someone please tell were this solenoid is? I'm just assuming that there's someone out there in radio land that knows the answer off the top of their head. I do have the thick three volume set of maintainance manuals, so I'll have a go with them tomorrow.
Thanks
Question: Somewhere, there's a electromechanical vacuum solenoid valve that applies or removes vacuum to the NPP lines. So, I guess the question for now is, ...can someone please tell were this solenoid is? I'm just assuming that there's someone out there in radio land that knows the answer off the top of their head. I do have the thick three volume set of maintainance manuals, so I'll have a go with them tomorrow.
Thanks
