2003 Lesabre not shifting from P to D or R

I have a 2003 Buick Lesabre, 3.8L, 54,200 miles. NO codes and no CheckEngine light on. Few months ago started to develop a slight jerk at around 25MPH so I changed the transmission fluid and filter, but no improvement. Then it started to have a delay in shifting from P in D or R, so I replaced all 4 transmission sensors, but again no improvement. Then the car started to stall and die at stop light or sometimes in the middle of the drive when slowing down, so I replaced the Crankshaft Position Sensor (CPS), I did the relearn the CPS procedure and car worked good for about a week. Now it looks that the car is back at not shifting from P to D or R unless I do the relearn CPS procedure, that being very annoying to do it every time you want to drive the car. After I do the relearn CPS procedure the car runs good with no problems but the next morning doesn’t shift again from P to D or R unless I do the relearn CPS procedure.


PLEASE HELP!!! Thank you in advance!!!

Did you read codes with an actual transmission reader or just a regular OBD reader?

I am using a Tech2 diagnostic tool scanner for GM cars, that the mechanics from the dealerships, Service Dept. are using. There are no codes, none.

Thanks for asking.

Have you load tested the battery and made sure the brake lights work properly?



-Rod

No, I didn't load tested the battery but the brake lights work properly. I have another 2003 Buick Lesabre that has no issues. Do you think that if I use the battery from that car it should solve the problem ? Thank you, I am appreciating any slight advice I get.
I just don't understand why after I do the relearn CPS procedure the car runs good with no problems but the next morning doesn’t shift again from P to D or R unless I do the relearn CPS procedure again.

Thanks again.

Yeah, if you have another car with the same size battery, it wouldn't hurt to swap batteries and see if it makes a difference. That will also give you an opportunity to inspect the battery cable connections at the battery to make sure they are clean and in good condition. The Tech2 should also provide a "System Voltage" datastream parameter too which can help determine if the charging system is healthy when the issue occurs.


-Rod

Thanks for the suggestion, I swept the batteries, but nothing changed. I just don't understand why after I do the relearn CPS procedure the car runs good with no problems but the next morning doesn’t shift again from P to D or R unless I do the relearn CPS procedure again.
Thanks again.

I don't even understand what a CPS relearn has to do with the transmission.

Likewise. With modern cars, if there's some strange electrical problem that doesn't seem logical, I tend to start my search with the battery. I've seen some very odd behavior caused by old, not even seemingly weak, batteries. It seems like when a battery hits 3 years old strange electrical problems start to occur. That even correlates nicely with the recent switch from 5 year pro-rating of batteries to 3 year replacement warranties.


-Rod

Exactly!

I am hoping somebody with a lot of experience in repairing cars will give some good advice. I bet there is a connection some how, some where, even though at first glance doesn't make sense.

I hate to put in the junk yard a car with so low miles...
Thanks for the comment.