my transmission will not down shift, when i start going it shifts through all the gears and gets to OD by the time i am going 35-40 MPH. and when i lay the pedal down it very slowly starts to gain speed, but will not down shift. also when going up a hill it will not down shift unless i do so manually. when i come to a stop it will go back down to 1st. has anyone had this problem or know what is causing this?

2001 ZR2 Automagic

 

Not being a tranny man, the only thing I can imagine that might be user serviceable is that the manual linkage is out of adjustment. Beyond that it is probably internal and a job for an auto trans shop. BTW,have you checked your fluid level and are you getting any DTC's?

 

On a 2001, this is all electronically controlled. I suspect there is a problem with one or more of the sensors on the engine. The PCM uses the requested torque value calculation to determine the appropriate gear to be in during operation. When you push on the throttle, this is communicated to the PCM through MAP, MAF, and TPS sensor data which all communicate that more torque is being requested. These sensors should produce trouble codes if operating outside of acceptable limits. If no DTCs are present, then this may be a problem with the PCM, but the diagnostic steps are pretty involved and require a Tech 2 scantool or equivalent.

 

Yeah my fluid is a champ, just changed the filter and added new stuff, and did the whole routine the manual says to do.
DTC's = Check engine codes ?
would a clogged CAT cause this?

 

DTC == diagnostic trouble codes so yes, check engine codes.

How does the truck accelerate up through the gears? How is your mileage? A clogged cat would limit higher RPM power by (in most cases) severely limiting exhaust flow.

 

the SES light was on yesterday and i was goign ot take it in and get the codes but it was off when i go in to go to work, it shifts smooth but its a little doggy, when i hammer down on teh pedal from a stop it starts going good then it just goes up through the gears, so by 35-40 its in od, the RPMS hardly get above 2500-3000 when i am flooring it

 

i just got my motor put back together on saturday night, and that was the first time i drove it, i bought it with a bad Intake gasket, so i never test drove it since i didnt want to mess the motor up any more than it may have been. if its not in gear it revs up good but when its in gear it does not.
also took about 1/4 tank of gas to go 110 miles, not sure how the milage is quiet yet.

 

From your description, it is possible that this is being caused by a failing or plugged cat (but again, this should trigger an SES light). But the fact that it shifts the same regardless of throttle position would lead me to believe that the PCM is missing part or all of the picture. You could diagnose a failing or failed cat by removing one of the O2 sensors in front of the catalytic converter and disconnecting the other. This will cause the truck to run in open loop mode and will set O2 sensor DTCs, but it will run. If the truck runs better with the O2 sensor removed, then you have a plugged cat. BTW, it will be loud so don't run it long!

I just posted the checks for determining if you have a faulty TPS sensor in another post. You should have a ground, +5VDC, and a signal wire on the TPS sensor located on the driver's side of your throttle body. If you find that you do not have the +5VDC reference, then something is wrong with the PCM as this is a PCM fed reference voltage. The gray wire should be your +5VDC reference, black == ground, and the dark blue will be your signal back to the PCM. These colors are correct for a 2000 engine, but I think they should work for yours as well. If you find that the voltage is correct on the gray wire, then move to probing the dark blue wire.

Here is a link to a pdf file that explains position sensors: Position Sensors - courtesy of Autoshop101.com

However, when the PCM detects a malfunction with the TP sensor circuits, one of the following DTCs will set:[*]DTC P0121 Circuit Performance Malfunction[*]DTC P0122 Circuit Low[*]DTC P0123 Circuit High[*]DTC P1121 Intermittent Circuit High[*]DTC P1122 Intermittent Circuit Low[/ul]So it looks like if there are no DTCs set, this may not be your problem.

 

I was going to suggest your governor is sticking. But it sounds more like engine problems.

 

ok so, when i went to lunch the SES light was on so i stopped in at AutoZone and got the following codes
p0118, p0122