I thouht I would share this with the club.I had shifting problems that would come and go. Hard shift 1 to 2 and sometimes no shifting( like all gears engaged at same time).To make a long story short it was a bad ign. switch sending bad messages to to trans solinoids
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Transmission not Shifting
- Thread starter sjudson
- Start date
Irontrain the mech. found it right away with the computor dia.The problem was a sometime problem that could be corrected by turning engine off and waiting 30 sec.
I had an intermittent shudder/slip during the 1st/2nd shift. I took it in this morning at 7 am. The mechanic called me at 10 am and told me he had a svc. bulletin on that exact problem that required cleaning the valve body and replacing the solenoid. So he did just that, and I had it back 1:00 pm. So far it is like driving a new truck, but time will tell. Will keep you posted.
Kephale
Full Member
RXA - any chance you have the TSB number for that? I've been in and out of the dealer 5 or 6 times now
with this and they claim no TSBs and they can't replicate the problem when I leave it with them. I've taken it in myself twice without an appointment and they heard it, but no idea what it is. The closest I've come is a TSB for Silverados that sounds similar (the charging system feedback mentioned in another thread), but they are skeptical since its for another truck (as am I a little). This might be the breakthrough I've been looking for (not that 
hasn't been fun 
)motrctyman
Full Member
There are a few things that can cause a harsh 1-2 upshift......I will do my best to remember what they are.
Like the original post, a "slightly" defective ignition switch can cause this. If it is "clocked" slightly off, the feed to circuit 1020 (feeds all voltage to the trans) will be late in feeding the Pressure Control Solenoid (PCS). The PCS will not get it's marbles back until the next key cycle (it's a PWM solenoid). This can run from extremely intermittent to every key cycle, depending on the switch. It can also set a boatload of DTC's too. This is a P/I in the GM system and goes back to 1996 if I remember correctly.
Remote starters can cause this too in the same way that an ignition switch can.....
Debris in the valve body will not normally cause a harsh upshift, rather a slip in the shift. Most normally due to debris in the A solenoid not allowing bleed off to occur quickly enough. However, if for some reason there was debris on the back side of the PCS valve, I suppose it could.....it just isn't that practical due to the flow of the fluid there.
A bunged up 2/4 band servo can cause lack of accumulator effect leading to a harsh 2nd upshift....
Obviously, a defective PCS solenoid can cause this and normally the only shift that is felt as "harsh" is the 2nd upshift as that is where there is the most torque multiplication.
Regardless of the other facts, the overwhelming majority of the problems are with the key switch. A lot of times there will be a repair to the trans then the key switch takes awhile to re-emerge......I can't explain why though.
Like the original post, a "slightly" defective ignition switch can cause this. If it is "clocked" slightly off, the feed to circuit 1020 (feeds all voltage to the trans) will be late in feeding the Pressure Control Solenoid (PCS). The PCS will not get it's marbles back until the next key cycle (it's a PWM solenoid). This can run from extremely intermittent to every key cycle, depending on the switch. It can also set a boatload of DTC's too. This is a P/I in the GM system and goes back to 1996 if I remember correctly.
Remote starters can cause this too in the same way that an ignition switch can.....
Debris in the valve body will not normally cause a harsh upshift, rather a slip in the shift. Most normally due to debris in the A solenoid not allowing bleed off to occur quickly enough. However, if for some reason there was debris on the back side of the PCS valve, I suppose it could.....it just isn't that practical due to the flow of the fluid there.
A bunged up 2/4 band servo can cause lack of accumulator effect leading to a harsh 2nd upshift....
Obviously, a defective PCS solenoid can cause this and normally the only shift that is felt as "harsh" is the 2nd upshift as that is where there is the most torque multiplication.
Regardless of the other facts, the overwhelming majority of the problems are with the key switch. A lot of times there will be a repair to the trans then the key switch takes awhile to re-emerge......I can't explain why though.
SpottyJ
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Just had new transmission programming entered by the dealer per TSB # 03-07-30-020B. What a difference it makes, tranny is MUCH smoother. I highly recommend you bring yours in for the programming.
zachandjake
Full Member
had the same thing, started, ran like crap, limped it to dealer, bad ignition switch.Replaced under warranty, shifts great and as wierd as it may sound, I feel like I have more power now . Which doesn't suck. 
I found this:
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(HTML inside the zip.)
I had a similar problem. When I stopped at a light and tried to take off, it acted like it was in 3rd gear. Ignition switch was bad. The only way the dealer figured it out was that I told them that one time when I started it, the odometer didn't light up. Hope this helps someone.