Alright, so I was driving down the road with the cruise set at 55, but then all of a sudden the car down shifted all by itself and I was now roaring down the road at 4500rpm...I pulled over, turned the car off for a few minutes, started it back up again, and it didn't do it again, what would cause this to happen? I do have some codes currently regarding excessive wheel speed variation in the rear, and some others dealing with the steering wheel position sensor if that helps....it has also refused to upshift sometimes when i first start it, It'll shift into second but then all of a sudden rev up to 4000rpm and sit there without shifting....all if this comes and goes so it has to be computer related or something I would think.
Did you get any codes dealing with the PNP safety switch, or TCC?
A reputable transmission mechanic told me this switch could cause the transmission to drop back into 2nd gear and and make the engine overspeed.
When He checked out my car 92 Deville 4.9, it would not manually shift from first to second.
After replacing the PNP switch it does like it is suppose to.
ok well now whenever i shift from park there is a nasty clunk, this just started, and the shift from 1st to 2nd is real jerky, can't seem to get her to work right anymore. Did my tranny just all of a sudden take a shit and die on me with only 100k on her??
This kind of reminds me of the crack sensors. Minus the downshift with cruise control on. But mine started with the jerky shifts then I lost my speedo and at that point it wouldnt shift at all. Might want to check your codes. Im pretty sure mine had them and I could clear them and the car would run fine most of the time untill I restarted. Oh and because I drove around a little while like that I needed my trans overhauled. Believe is was $1500 or $2000.
well I started it after it sat overnight and everything is fine...no clunk, shifts smoothly into all gears, this is strange?!? I called the Cadillac dealer that I bought the car from and explained what the car was doing and the mechanic said that since it happens randomly with no definite cause he was almost positive it wasn't mechanical at all. He said either a sensor is on the fritz and is in need of replacing or there might be something floating around in my fluid...he told me to go get a trans. flush and see what happens...figured that wasn't a bad idea since I just rolled over 100k yesterday
To add to what dp102288 said,
AKA DTCs (Diagnostic Trouble Codes). The car is loaded with sensors. When one fails or recieves bad data it sets a DTC which in some cases (emission related) will trip the SES light. Some body or chassis DTCs will set a service message like service suspension system or service tire pressure monitors. Others won't set any messages if they are not critical, like heater control doors out of range.
^^ Codes are info that the computer will set in memory to indicate what is wrong/happening with the car. An example could be P0420 whcih will cause the service engine soon light to light up on your dash. This codes, if read from your car, will tell you that you are having an emission problem.
Codes are what the dealers use to quickly tell what's wrong with a car, so they know which specific system in the car to start troubleshooting. That is why we like to know because it gives us an indication of which system is causing a problem. Coeds can be for the body, powertrain, suspension, and other specific systems.
Check the How To forum to learn how to pull codes and a better explanation on them.
Well I got my trans. flushed out and the problem is still there...although she sure shifts a lot smoother when it decides to work the codes I have are
c1227. 1228, 1248, 1255, 1287, 1288, and u1000. All the chasis codes, I was told, are being set off because my steering wheel position sensor has gone bad, don't know what the other one is all about...no codes relating to the transmission or anything that controls it at all...I don't like having problems that don't have an explanation
C1228 - Right Rear Excessive Wheel Speed Variation
C1248 - EBCM Turned the Red Brake Warning Indicator On
C1255 - EBCM Internal Malfunction
C1287 - Steering Sensor Rate Malfunction
C1288 - Steering Sensor Circuit Malfunction
U1000 - Class 2 Communication Malfunction
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