While towing my 5er, at one point along my trip from NY to KY, it seems like my grade braking quit working... Before, if I held the brake going down a hill, it would downshift... If I kept holding the brake to slow down more, depending on the hill and my speed, it would downshift again. Allong the way, it stopped doing this. If I held the brake, the truck would slow down using the brakes until 55 or so (the 4-5/5-4 shift point) but I was no longer able to get it to downshift sooner than that ore more than that, and there where a few times where it should have and I would have liked it to.

The only codes I was able to pull are B0229 - Recirc Position Feedback ckt range/performance and B3770 - Airflow Control 6 feedback ckt. If I understand them right, they are being set by the BCM, and have nothing to do with anything related to the drivetrain.

Any ideas what could have caused the grade braking to seem to quit without any codes?

I would be willing to bet that you were NOT in T/H mode.

The ally will not do grade braking in normal mode and at 50 mph will drop to idle.

I think that is stupid and gm should have provided for as much deceleration braking as possible.

My .02

Cougar, just noticed a similar problem on my truck. When towing and desending a hill I can stand on the brakes but get no downshift until 50 mph. My trans was in T/H mode when this occured. Just returned from a trip of several thousand miles (towing) and haven't had a chance to get it to the dealer.

I have a Van Aaken box, could this be the problem? No I didn't try turning it off, I keep the switch on the low setting and wasn't sure which position was off... didn't want to switch to high by mistake and possibly hurt something.

Has your trans had a chance to learn with the VA box. If not it may be a bit confused.

The VA box has been on for about 5K miles no other issues with it and I just leave it on the low setting all the time.

The grade braking feature is active in all transmission modes, not just T/H.

Due to the different shift programming, the grade braking will be different in normal mode vs. T/H mode.

The bottom line is, you won't get the grade braking you think you want in normal mode. It's still there working, just different.

Cougar

Had the same thing happen yesterday. I would get the down shift but no assisted grade braking. With the edge I was able to tell that the torque converter was not locking up. Went to park and I had lost "reverse" with a DIC message of "Shift Range Inhibited" no other warning lights. Drove it to a place that "reverse" was not required and had gears 1 thru 4 with no problem. Don't know about 5 as did not go fast enough to need it. Turned engine off restarted, same message displayed. disconnected both wire bales on engine and reconnected. Started engine and reverse was working again. Took to dealer they found a P0742 had been set, they were not able to look at it further until next day. Drove it home for the night and back to the dealer this morning, no additional problems. Just got a call from the dealer as I was typing this. After further investigation, service advisor told me, they have replaced the NBSU?(Park neutral switch).

Cougar

Had the same thing happen yesterday. I would get the down shift but no assisted grade braking. With the edge I was able to tell that the torque converter was not locking up. Went to park and I had lost "reverse" with a DIC message of "Shift Range Inhibited" no other warning lights. Drove it to a place that "reverse" was not required and had gears 1 thru 4 with no problem. Don't know about 5 as did not go fast enough to need it. Turned engine off restarted, same message displayed. disconnected both wire bales on engine and reconnected. Started engine and reverse was working again. Took to dealer they found a P0742 had been set, they were not able to look at it further until next day. Drove it home for the night and back to the dealer this morning, no additional problems. Just got a call from the dealer as I was typing this. After further investigation, service advisor told me, they have replaced the NBSU?(Park neutral switch).

Which truck?

The grade braking feature is active in all transmission modes, not just T/H.

Due to the different shift programming, the grade braking will be different in normal mode vs. T/H mode.

The bottom line is, you won't get the grade braking you think you want in normal mode. It's still there working, just different.

It works better in T/H because the TC is locked. At least that's what I think.

It was in T/H (unless it's possible to not be in T/H even with the light lit)... No power adders of any kind... bone stock except for the MBRP front pipe.

On the transmission note, I took an '06 for a ride today... LOVE the "manual" mode... doesn't make the transmission work exactly like a manual (if you put it in 2, 3, 4, etc, you still start at 1), but the manual downshift is NICE. Now need to figure out how to add the 4th gen TCM, the bypass tube, DIC functionality and the new shift lever...

Which truck?

This happened on the '04

The NSBU switch if it fails on the newer models is rare. When it downshifted did you have it in T/H mode? If you did try it again since you had the switch replaced and see if it fixed the problem.

The NSBU switch that was on the truck from new was the old version (black one). I assume that is the reason it failed. The down shift was when it was in T/H mode but the edge box showed that the TCC was not engaged at any time. There was also no feeling of grade braking to assist with the truck brakes. After disconnecting/reconnecting the wire bales under the hood the TCC would lock/unlock as normal.

The shop forman informed me that the replacement of the NSBU really only related to the 'Shift Range Inhibited' message that I had, not any hard codes being set. Here's hoping that it's not the TCC going south right when I need it.

By wire bales I take it you mean the wire harness connectors for the J/A? If so make sure all the pins in the connectors aren't recessed and are in a good position to make good contact.