2004 Cadillac CTS Engine size 3.6L. Transmission programming reflashed
Question = Hello,
I have an 04 Cadillac CTS with the 5L40E transmission. About 3 months ago it developed a problem
when trying to take off from a stop, the engine would rev and then slam into 1st gear.  I took it to a
dealership but they couldn't replicate the problem.  The only codes it was throwing was for a misfire
in cylinder 6.  They changed the plugs but also reflashed the programming. This didn't fix my
problem.  Now the car will creep along in first until going fast enough to go into
second.  It shifts
through all the other gears fine but doesn't go into overdrive.

This transmission is a sealed system so I can't check the fluid level except through the fill plug.  I
plan on changing the filter and topping the fluid back off to see if that helps.  I know that there are
solenoids that control shifting so I'm wondering if one or more of them is going out.

Would any one solenoid cause the problems I am having or is this an issue apart from a solenoid?  
Any advice?

Answer: Yes, it does sound like you may be having a problem with a solenoid or valve body. There
are many different solenoids in your transmission. There are more that just shift solenoids, which
are a common part to fail. Your Cadillac has others that can cause the problem you are having.

One possibility is what is called the "Pressure control solenoid." As it's name states, it controls
hydraulic shifting by changing the pressure in the system, namely the valve body and other circuits.
A problem with this would usually set a check engine light. There are actually several GM service
bulletins for shifting problems on this car. The dealer would have looked through those that match
your problem, even if they did not experience it.

You should try a filter and fluid change. You may also want to add a cleaning agent before that and
drive the car a few miles to get it hot and circulated first. If this does not help, you are best to leave
it with the dealer until they can feel the problem for themselves, watch live computer data and
decide if it is electrical or mechanical. If mechanical, the transmission would need to be removed
and disassembled to find the problem. This can be very expensive.
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Cadillac CTS Transmission Slams Into Gear