Range Shift Inhibitor

[snoose]

Hi,
Have a 2003 Chevy 2500 duramax/allison. This morning went out and started up and the engine lights on and when I shift into reverse it says Range Shift Inhibitor, and won't go into reverse. Goes into Drive alright, but makes a loud clunk when doing it. It did this 1 time before and my father-in-law put some trans fluid in it and the problem went away, well my dad checked it and the fluid levels and it was fine. My hubby is in Iraq right now otherwise he'd probably know what to do, but I'm not that mechanically inclined... Any help would be appreciated. Thanks. Ashley

[semperfidoordie]

I would try climbing under the truck and checking the passenger side of the transmission. There is a round plug that may be not plugged in well or may have come loose. I'm no expert but when I did my trans that's exactly what mine was doing and it was because that plug was loose. Hopefully Mike L or Dustin will see this and can give you an experts advice. Otherwise if it's not what I said try looking up Inglewood Transmission Service, Merchant Automotive, or Diesel Addiction and call them

[p_bol]

Originally Posted by snoose

Hi,
Have a 2003 Chevy 2500 duramax/allison. This morning went out and started up and the engine lights on and when I shift into reverse it says Range Shift Inhibitor, and won't go into reverse. Goes into Drive alright, but makes a loud clunk when doing it. It did this 1 time before and my father-in-law put some trans fluid in it and the problem went away, well my dad checked it and the fluid levels and it was fine. My hubby is in Iraq right now otherwise he'd probably know what to do, but I'm not that mechanically inclined... Any help would be appreciated. Thanks. Ashley

Sounds like a bad NSBU. Look at the top of this section for the "NSBU Replacement Instructions and FAQs" thread. There is a lot of good info in the thread (i.e. What are some of the symptoms that the NSBU switch is going bad?) and it will give you step by step instructions to replace it. When I replaced mine I had to heat up the connectors with a heat gun to get them to release.

If you decide to replace the NSBU and do it yourself call around to various Allison dealers. I was quoted over $200 at one dealer and $76 at another. The GM dealers want crazy money for these things, hence the Allison dealer. You can find the closest Allison dealer to you off of their website. If you do not have a close dealer try a supporting DP vendor.