Big trouble in Dmaxland.

[stevem]

2001 D/A with 3,300 miles.

Monday morning while driving on the freeway at 65 mph the engine speed all of a sudden dropped down to idle and the trans went into neutral. Pressed on the accel pedal, engine still at idle. Pulled over and shut the engine off and then back on, now all is ok and I make it to work without a problem.This occured 5 miles into my drive to work.

Monday night on the way to the dealer almost the same thing occured, but this time I did not have to pull over and cycle the ign switch.This time the trans downshifted to third, rpm went to 3,600 and then the trans shifted back to overdrive and away I went. This occured after about 20 miles.

Both times no warning lights or prior running problems.

Dealer called Tues and said no faults stored and could not confirm the complaint.Shop foreman now has the portable diagnostic tools hooked to the truck while he drives it to and from work 50 miles.

So what do you think it could be? Any tech tips I can relay to the dealer??

Grumpy in Dmaxland, Steve.

[ChevysRus]

a while back there was a report about a wire chafing that runs along the transmission. This can cause a short in the electronics that is hard to find since it doesn't do it all the time. You might try a search and see if you can find the message. otherwise get under there and check all the wiring running to the trans. One of the wires may have worn off the insulation and causing a gound short when it touches metal.

Otherwise, you will have to try and let it fail again so they can figure it out. Could be a switch failing or something else. It should not be fatal, just aggravating until they figure it out.

Good Luck and don't lose faith

Regards

[mdrag]

IIRC, there was a post describing wires chaffing due to hose clamp positioning on the power steering pump - very easy to check for but easy to overlook unless you were looking for it. I believe some of the affected wires are routed to the tranny...worth a quick look.

A few members posted they had to reposition the clamp, and it had started to rub through the split loom but had not yet damaged the wires. Good luck.

[ 04-17-2002: Message edited by: mdrag ]</p>

[mdrag]

Found the link to the previous post describing the PS clamp problem:

http://forum.62-65-dieselpage.com/ubb/ultimatebb.php?ubb=get_topic&f=7&t=001957

[stevem]

Thanks Guys.

Keep those tips coming.

Steve

[matt-max]

just had the asme thing happen to mine...maybe

did the illuminated square indicating what gear you were in disappear?

mine did and selected only third gear and reverse, occassionally and only with a bang.

lucky me, i have an allison engineer for a neighbor who came over and fixed it on the spot by replacing the neutral safety backup sensor (i believe thats what he referred to it as)

matt

[hoot]

Sign of a possible bad NSBU switch. The black switch mounted on the side of the trans where the shift cable hooks.

[sonofagun]

I am pretty sure it was HOOT that posted (and had pictures) of a switch along the side of the transmission that could cause such a problem. HOOT ya out there on this one?

Bob

[sonofagun]

hoot,

You beat me to it............

[Kennedy]

The first thing I would do is make sure ALL calibration updates have been performed including the ait box. This will eliminate any false codes from occurring.

[Turbo Al]

I second err third the NSBU swith -- dead give away is the square light on shifter is NOT there.

[RWHP]

This is the exact same problem that my truck was having. It is due to a faulty sensor reading, however mine was storred in the ECU as an error code.

The fix was to update my ECU software, which was performed and the problem was gone. Look for my post about 1 month ago and it describes the error code I got.

[stevem]

Dealer was able to confirm the running problem.
Here's what is written on the repair order.
"Traced and found bad prong at E.C.M. Repaired prong.Extensive road tested OK"

I put 100 miles on the truck since the repair, so far so good.

I also complained about lack of power at 2,000 rpm and above. Told them that I noticed this problem right after the software updates performed Jan 2002.Dealer said.

"GM is aware of this situation and is working on recalibration software.Should be available in near future".

Steve.

[ 04-20-2002: Message edited by: stevem ]</p>