trans slips on highway downshift with SES light - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-02-2003, 04:22 PM   #1
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Default trans slips on highway downshift with SES light

I have a friend'* 1995 SSEi while he is out of town to replace the supercharger coupler. While I'm working on it, I'd like to see if I can help repair (or at least diagnose) a few other little problems.

The SES light comes on after running for about a minute. Engine has no hesitation but I seem to remember it having a bit more power when I drove it last year (could just be the trans feeling more sloppy). The transmission shifts very smooth, but when at WOT, it doensn't downshift, it just falls into neutral and the engine winds up to the rev limiter, or falls back into overdrive when I let off. (I only did that once on the highway)

I dont have a code scanner at my disposal right now but he said he checked it and it was setting a P0640 or a P1640, I'm not familiar with OBDI nomenclature. Could the trans problem be causing an SES light, or is it just worn and most likely unrelated? The car has 131,000 miles and has been very well maintained.
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Old 08-03-2003, 09:07 PM   #2
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The P1640 is a code representing the Quad Driver No. 1, which controls the boost control solenoid, the charcoal canister solenoid, and the TCC apply solenoid. When it detects an improper voltage it sets the code.

Sounds like a problem with the TCC solenoid or the wiring to it. Do the cooling fans operate? They are on the same fuse.
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Old 08-04-2003, 12:38 AM   #3
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Thanks for looking up the fault code

dont know if the cooling fans are working or not, I haven't really driven the car and now it'* apart until I can get a supercharger gasket to throw it back together. Tomorrow I'll check if the fan circuit is allright, though it didn't run hot when I drove it over here. The wiring is all original (an aftermarket alarm/remote starter was installed)
I know that 200-4r/700-r4 transmissions are well known for TCC failures on the solenoid itself. Is that also prone to fail on these cars? I would imaging that could cause the ECM to read an out of spec voltage if it can feed back.
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