Why does the transmission "slam" into drive from neutral? This is on a 1999 chevy cav.

First make sure the fluid is full. If it is then you have internal problems. Possibly the linkage or oil pressure .

run fault codes
shifting to neutral would cause no problem but shifting to reverse will destroy the transmission and drive train slamming your face against the wind screen
If that hasn't happened then may be it is a selector light that is incorrect could be a problem harness connection to the transmission

hi Bobby.
this is all i could find.
see if this helps you out.
where is the neutral safety switch on 2006 chevy impala Google Search
or read this.
Where is the neutral safety switch? Column shifters have the neutral safety switch located on the of the transmission. Mechanical floor shifters have the neutral safety switch located on the of the transmission. Electronic floor shifters have the neutral safety switch in the shifter housing and a gear position switch on the transmission.11 Aug 2016

How to Replace a Neutral Safety Switch ' YourMechanic Advice

https://www.yourmechanic.com/.../how-to-replace-a-neutral-safety-switch-by-marvin-su... Search for: Where is the neutral safety switch?
or you could go to this link and it should help you out some more.
where is the neutral safety switch on 2006 chevy impala Google Search

Start with a cheaper solution, try cleaning up as many grounds on the vehicle that you can find, good possibility that your problem is just a bad ground somewhere. Check condition of ground strap that goes from the engine to the frame of the car, on my 94 cav it is bolted to a stud at the engine to transmission mount bolts and goes to the frame.

I would recommend replacing the in-line fuel filter

check fluid level, make sure proper fluid is in transmission otherwise take to trans shop to diagnse if level and type is correct(check at idle normal operating temp)

You need to take it to the shop to be repaired this is not going to be an easy fix. It is probably going to have something with shift solenoids or fluid pressure. Have the tranny serviced by replacing the filter and flushing out the system.

check transmission fluid level, vacum leak.or wiring,transmission solenoid ,sensors. or hope not. bad tranny....eeecchh

hi i have the fault code here and it says gear 4 incorrect ratio.wiring fault,transmission switch,shift solenoids or mechanical faults in the gear box.hope this helps ,best of luck.

Your vehicle has the 3.4 ltr engine and the 4T65E model transmission,which i have rebuilt many,many of.First,verify the transmission fluid level is FULL,and not low,also verify by pulling the pan,that the filter is in place.If all that checks out,then the problem is internal.For the problem you are describing,there are two areas to address.The first,which can be checked outside the trans with a 0-300 psi gauge is the EPC solenoid.EPC stands for Electronic Pressure Control.It is an electrically controlled solenoid that regulates mainline pressure inside the trans.The OEM (original equipment manufacturer) solenoid is known to be problematic,and erratic,causing your vehicle's symptoms of neutralling out,and slamming back into gear.The other area is the Forward piston inside the Forward/3rd gear input drum.The steel piston gets a ridge worn into it,and when it tries to apply at a stop light upon taking off,the ridge causes the piston to hang up momentarily,and then when it frees up,again,a neutral/slam into gear.Common problem that i have had to address over and over on these transmissions.Good luck.