Question about 1997 Pontiac Grand Prix

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Transmission issue? Or worse?

1997 Grand Prix GT 'died' last week. Dropped new transmission in, car now goes into gear again. Now the problem is upon acceleration, for instance taking off from a stop light.. the car stalls and just barely moves past 10 mph without pushing the pedal to the floor. Once this is done the car flies upward to 50 mph and seems like it won't go any faster??? Before old transmission failed, the car would accelerate easily 0-60 mph in a lot less time. Also, ABS light stays lit & Traction control light will not stay on flashes back to 'Trac Off' setting??? Help!!! Thanks...

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  • tar1978 Feb 03, 2010

    Hello & thanks for the quick response! To answer your questions:

    1. 1997 Pontiac Grand Prix GT
    2. The SES light is on and won't go off
    3. Unfortunately, the transmission is a used unit (couldn't afford a brand new one..)

    This is very helpful information in trying to figure out what's going on with my car. Could the above problems cause the car to slightly overheat when in drive (w/ foot on brake like when stopping at a light) or in park?? I noticed this today. Whenever I was stopped at a light or in park, the temp on the car seemed to climb higher and higher..almost overheating??? As long as the car is moving it tends to keep a lower temp?? I really love this car (only had it about 10 months) but it looks like I'm running into some major problems already...



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Hello! Although the symptoms you've described could be a result of quite a few things, I have a few questions that might help determine your problem.

1) What year/make/model did the new transmission come from?
2) Is the SES (Service Engine Soon) light on? Is it blinking?
3) Was this transmission a rebuilt or used unit?
Some possibilites:
- you could have a faulty TPS - or Throttle Position Sensor.
- you could have a problem with the input shaft piston being worn. (Hence the used vs. refurb trans question). Once the inner sealing area wears it can prevent the inner lip seal for the piston from sealing properly. You may find that revving the engine up will finally get the car to move and it will BANG into gear. This is because the pump in the transmission is working harder and moving more fluid thus allowing the added fluid to overcome the leak which prevented the clutch from either initially applying or staying applied. Another area of concern that causes this is a boost valve in the valve body, not near as common but it can cause this problem on a lessor scale.

- Trouble Code P0742 TCC Stuck ON:
When this trouble code is set the pcm will command max TCC and lock adaptive shifting. This code can be broken down into three potential problem areas as found to be common in the field.

1. This problem can be a mechanical problem. Possible causes of this could be a bad or stuck TCC switch that signals the pcm of current TCC operation. Another cause though not common is a stuck TCC switch or apply valve. If it is physically stuck in the wrong position it can cause the TCC to be stuck on all the time and even kill the engine when the vehicle is put into gear.

2. This problem can be found to be an electrical problem. If the wire from the TCC pressure switch to the pcm is grounded anywhere in the path it can throw this code. This could be a wire shorted inside the trans on the internal wiring harness or the actual engine wiring harness. If the wire is grounded the pcm thinks that TCC is on when it shouldnt be and will throw the code.

3. This problem can be a hydraulic problem. This is the most common cause of this code that I have found and stems back to a clogged TCC solenoid, not because it failed. Excessive debris in the transmission or a failing torque converter lockup clutch can cause the solenoid to have debris stuck inside and this causes a restriction in fluid flow through the solenoid. If the solenoid can not bleed off the pressure the TCC can be stuck on. If the wrong TCC solenoid is installed during an overhaul this problem can also arise as a late 4L60E solenoid is identical but does not operate the same and acts like a clogged solenoid. As mentioned in problem #1 a stuck TCC apply valve is a physical problem but causes a hydraulic problem because the fluid pressure will not properly bleed off because the valve is stuck in the wrong position instead of being able to move freely in the bore of the valve body.
Above are the common causes of this code, there are other possibilities but those are what generally causes the fault. A thorough diagnosis is the only way to determine what is really at fault and a new TCC solenoid should never be assumed as the actual problem until verified.

HTH - and thanks for using FixYa!


Posted on Feb 02, 2010

Testimonial: "Excellent feedback, thanks!"

  • Shannon Washam
    Shannon Washam Feb 03, 2010

    Hello! Thanks for the additional info. Well, it is a plus that the replacement transmission came out of a '97, it takes incompatibility out of the equation. FYI - you can swap the transmission from any GT from 97-03, but you cannot swap the transmission from the GTP (supercharged version) in to your car - one is an electronic trans and the other is hydraulic, and the gear ratio is different as well. If you're at all unsure as to whether or not the replacement came from a GT vs. a GTP - you need to determine that with absolute certaintly before continuing. I have a good friend that works almost exclusively on these transmissions, and is in my opinion, the most knowledgeble when it comes to them. You can view his website here. On his site, he explains how to locate the ID tag on the transmission. I've included a picture below as well. If you can locate this and contact him (Dave) he can help you determine if it's a unit out of a GT or GTP. Also, if you're in or near Indiana - I would suggest having him rebuild a unit for you.

    My inclination is to tell you that you may have swapped out a transmission with one set of problems - to another one with a different set of problems, unfortunately.

    Picture of the location of the transmission ID tag:

    You can locate this by looking under the passenger side of the vehicle.

    As for the overheating issue - no, the transmission shouldn't have any impact on the engine temperature as they have separate and unique cooling systems. What may have happened though, since you mention that this isn't an issue while the vehicle is moving, is that the fans may not be coming on. There can be a few reasons for this - but the simple fix might be that they just got unplugged during the transmission swap. Your car actually has 2 fans, and there is an electrical connection between them - check to see if it is unplugged. Do the same for the temperature sensor as well. One other option is to take the car to any major auto parts retailer and have them scan the car - they will have an option to place the vehicle's computer in "Diagnostic" mode - and manually turn on the fans from the menu. If they can do that, then it rules out the fans being inoperable.

    I hope this helps, I know it's a lot of information. Thanks for using FixYa!




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