I have a 2004 LB7 Duramax with about 120K miles, 285/75/16 tires, suncost 4, and tuned with efi live. otherwise stock

truck runs good makes plenty of power shift fine but..... one out of every 5 to 10 "stops" i get a "buzz" in the brake peddle and the DIC will display "shift range inhibited". i can move the shifter into "N" or "3" and back to drive and it will work fine for a little bit then do it again when coming to a stop.

once when pulling into a parking lot it happened and i also had the "service brake system" come on the DIC and the ABS/brake light cam on. before i was getting no codes but when this happened i checked it and got P0880 and C0055. the description of the codes makes sense fror the problems but what is causing them???

i have read some other forums and it seems the most common fix is the NSBU switch and ignition switch. i was not able to find anyone with my same symptoms so i tried the ignition switch and still have the same problem. should i replace the NSBU switch? checked NAPA and it was about $220 - ouch

let me know what you guys think, hope this wasn't too long for you

thanks Jason

 

ok, i tried cleaning the ABS ground under the driver door, check the pins at the TCM all in place none pushed out, etc. measured the #1 pin black/white wire on the gray connector to ground and was less then 1 ohm. does anyone know what pins are supposed to have 12+ volts?

took it for a test drive, still the same problem. seems to me that it has to be connected to the ABS/brakes somehow, maybe with the wheel sensors?, as it only occurs while applying the brakes.

is there another ground i need to clean?

thanks Jason

---AutoMerged DoublePost---

well it seems that when i am running in "tow Haul" mode (without a trailer) it has no problem. when i put it back to normal mode and push on the brakes it will go into the "shift range inhibited".

anyone have any ideas on what i should check next?

 

have you reflashed the TCM with your efi live? i would try that also

 

are you thinking flashing in the stock tune or reflashing the current tune? i raised the shift points some on my current one, and it has been working fine for some time now. is it possible that the tune is corrupt and flashing it will correct it?

 

i would start by flashing it back to stock yes, for us that is allways the first step is to take away anything that isnt stock just to make sure that isnt the problem. reflashing it will also force the trans to relearn and also check the box that says reset taps

 

thanks, i will give it a try and let you know.

 

i believe it is the mounting spot on the hubs where the sensors screw in it gets rust under it and pushed the sensor away from the rotor it is pretty common and is a service bulletin. the fix is new hubs or pull the sensors out and clean surface with emery cloth hope this helps.

 

I reflashed the stock TCM tune in and reset the taps. i have not driven the truck much this week end + its still learning the taps. otherwise it seems to be ok.

I like chevyhoss' idea on the hub sensors and will give that one a try today.

before i put the stock tune back in i noticed that, whenever the tranny would drop out of gear and display the error msg, the speedo Needle would jump down a few MPH. because the code i was able to pull out of it earlier that indicated both speed sensors i suspected it had to be an electrical problem as i doubted that both would go out at the exact same time. but maybe i am making it more then it is and it is just the sensors.

well i will see how it goes and let you guys know

 

is it possible there is 2 different problems we are dealing with

 

so, i took a look at my front wheel sensors. looked fine to me, no rust. pulled them out and put a meter on, was able to detect metal objects with it. not very scientific but enough to convince me that they work.

ran the stock tcm tune in for, 1 1/2 days, approximately 30 miles with no trouble. put my other tune in and almost immediately problems. looks to be my tune. thank you cummin_un_glued for helping me on this.

comparing the two tunes i noticed that the 2-1 shifts at zero throttle was at 9 mph, stock was 5 mph. must have accidently copied T/H to this area.???

anyways 9 mph was right where the problem would occur. so i changed this area back to the stock mph and reflashed the tcm. drove home, 15 miles, and so far all right, crossing my fingers.

if this takes care of the problem then i am good. if i am dealing with two problems then hopefully it will be easier to find when it resurfaces.

i will keep this thread open for a a few more days just in case. thanks you all for your help so far.

Jason