Hi guys, Im having problems with my car down shifting and pulling hard. Its a 97 with an a4 transmission. It shifts totally fine under normal driving but when I go to full throttle the car doesnt take off. It does down shift but it doesnt pull at all. It almost feels as if its missing more than half of its power. It just started to happen in the past few weeks and I nor my mechanic can figure it out. I had my mechanic run a scan while I was driving and the engine scan checked out fine but it was unable to communicate with the transmission. He couldnt figure it out so I thought that I would ask you guys what you think it may be. Is there any relays that I should be looking for? Is there a seperate transmission computer? It did pull a p0748 code that we couldnt find out what it was and it also pulled some kind of traction control code. Any help would be very appreciated. Thanks, Tony.

 

Just looked in my 2000 Service Manual, and the title is DTC P0748 Pressure Control Solenoid Circuit Electrical.

After the long descriptive paragraph, it says, "When the PCM detects a continuous open or short in the PC solenoid valve circuit, the DTC P0748 set. DTC P0748 is a type C DTC.

Hope this helps in choosing a direction for your troubleshooting.

Tim Glover

 

Thanks for the info.

 

What kind of scanner is your "mechanic" using ??? Whatever it is obviously is incompatible with a Corvette .... The PCM (POWERTRAIN Control Module) controls both the engine AND the automatic transmission.

One of the things the PCM controls is the line pressure in the transmission. It does this by controlling the Pressure Control (PC) solenoid valve which is located inside the transmission. The P0748 is the PCM saying that it cannot communicate with the PC solenoid valve.

This problem can be caused by ....

* a wire has been cut or come loose in a connector.

* A wire has lost its insulation and is grounding against metal

* The PC solenoid valve has failed

On the right side of the tranny case there is a 20 wire round connector. At pin C (Purple wire) is the PC Solenoid Valve High Control. At pin D (Light Blue wire) is the PC Solenoid Valve Low Control.

I'd recommend you take the car to a dealer or a shop more experienced at working on a Corvette. I would not consider your "mechanic" qualified as he doesn't have an imporatant diagnostic tool (Tech2) and does not have Service Manuals for your car.

The Corvette is a complex vehicle, the Service Manuals for one Model Year run to several thousand pages. Without the Manuals your "mechanic" should not work on the car.

 

Thanks for the info blackz06.

 

I can see this thread is old by it came by the search, so I hope somebody can help me..

I have a 98 C5 with just 8k miles.
I decided to do an aftermarket tuning with a guy that do that here on México and do that to many people so, I wanted to increase performance without any internal mod.

Since the car was tuned/reprogramed, I noticed that sometimes the car kick hard, and sometimes, works just fine.
I notice that if I turn on the car and drive normally, all the way goes to the upper shift totally normal, but, If I goes WOT, from there till I turn of the car for a while and then turn it on, kiks all the shift harder, SO, Im asking the guys that have that same problem, if they performed an aftermarket tuning becausea I can see that MAYBE, in the process of perform shift/speed or something, maybe the programmer leave the program great in that exact minute but didnt see that if at other parameters will present this failure because the shift isnt at the right speed.

I really dont know, but, I just figured out that might be just a little adjustment on the programin because the Camaro I had, had the same problem and was tuned too.

What do you think?