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99 Safari: shifts hard intermittently..no fault codes..service light…

Customer Question
I have a 99 Safari...
I have a 99 Safari that shifts hard intermittently from first to second and somewhat hard from second to third. This problem has appeared once three months ago and then disappeared till now. There are no fault codes and the service light is off. Two days ago I had the transmission fluid changed and included an additive to help with leaks and hard shifts. This was done and recommended by my neighborhood service garage. The hard shifting has since become more consistent. Can you offer some sort of explanation and coarse of action?
Kind Regards
Siegfried
Submitted: 8 years ago.Category: GM
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Answered in 7 minutes by:
6/17/2010
GM Mechanic: Steve, GMC Technician replied 8 years ago
Steve
Steve, GMC Technician
Category: GM
Satisfied Customers: 120
Experience: ASE Master, L1, GM World Class, 20 Years GM Dealership Eperience
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Siegfried, you have a 4L60E transmission in your van. A harsh 1-2 shift is a common concern I deal with alot. The most common cause of this concern is, a P1870 being set in the PCM. You have said there is no codes?? The code can be set with no light on. If the harsh shift continues with no code set, you will need to have a line pressure test performed. The pressure in the transmission is controlled by the PCM through a solenoid in the valve body. I hope this answers your question
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Customer reply replied 8 years ago
The local mechanic checked for fault codes and his reader came up with no codes being set in memory. Is checking the presure in the transmission a difficult task, would he be able to do this? What is an acceptable presure reading? If the presure is out of spec., what is the next corse of action?
GM Mechanic: Steve, GMC Technician replied 8 years ago
I dont know the extent of your local mechanic, so I dont know the answer to that. I just keep getting back to you having a P1870. I would think that you need to have someone who is a qualified transmission technician look a this for you.
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Customer reply replied 8 years ago
Can you define a P1870?
GM Mechanic: Steve, GMC Technician replied 8 years ago
P1870 has to do with excessive TCC slippage. Its a very common condition with your trabsmission
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Customer reply replied 8 years ago
What is the sollution to this problem?
Is it an expensive fix?
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