Bad Shift Solenoids without PCM code possible????

So last week the transmission on my 96 Aurora (4t80e) started acting exactly like all the symptoms i have read on here regarding the bad solenoids. Harsh 3rd to 2nd downshifts after warm up, not wanting to shift from 2nd to 3rd, reving up while in 3rd gear "speed" but actually not being in "gear". It was spot on the same problem. Just kind of lost in terms of what ger it wanted to be in and always seemed to want to get into 2nd gear when it didnt know what to do.

I really really wanted to just do the solenoids but i have been having code 716 for a couple of months which is intermittent input speed sensor. Yes that. I checked again with my cheapo scanner after the recent problem showed up and discovered now i also have code 717 which is no input speed sensor signal. Figured it went from bad to dead. Checked resistance through harness and nada so i figure okay the speed sensor is making the tranny act whacky.

I get the speed sensor changed, yes the cradle dropping case cracking ordeal to change the $20 sensor. Really not as bad a job as i thought. Valve body diagram from the cadillac forum a HUGE help. In my garage with a floor jack, 4 jack stands. Heat (if you do it in the winter in a cold region) and air tools are a must. Cant drop the cradle or pop the axle without a real good impact. Air ratchet helps make tear down go sooooo much faster. Four hour tear down, five hour assy. Much much faster next time around, lol.

So anyway get sensor changed, do the right thing and change all the related gaskets and seals. Thats another 100 in parts and 50 in afreeze and tranny fluid and i am all good to go for a 200 bill. NOT !!!!!

Road test it and the tranny shifts like before but hey at least the codes 716 and 717 are gone. I will tackle the solenoids next, should have done the wrong thing and did the cheap fix first!!!!!

Has anyone ever had bad solenoids but never got the code for them? I am going to change them but if someone else had bad solenoids with no code it would make me better that i stand a chance at fixing this thing for just another 60 bucks.

Thanks

I think it will because there are so many sencers on the engine, there should be one on there. also, where is Wilbraham by? I used to live on Holyoke, thats why i ask. i heard of it, but unsure where it is.

There are no sensors near the solenoids. The PCM does monitor current and voltage of the solenoid and that in turn can generate a code. There isnt a physical sensor detecing physically what the solenoid does it is only monitored via electrical characteristics. Thats why i am trying to find out of anyone ever had one electrically okay (passes the diags) but physically not working.

Wilbraham is east of Springfield, home of Friendlys.

Thanks for taking time to reply.

I think it will because there are so many sencers on the engine, there should be one on there. also, where is Wilbraham by? I used to live on Holyoke, thats why i ask. i heard of it, but unsure where it is.

The computer doesn't monitor the electrical characteristics of the solenoid. It doesn't even know if it engages when it tells it to directly. What does do is look at the input and output speed sensor. It can use these two sensors to determine the gear that the transmission is in, based on the ratio that the two are spinning at. It sets the fault if it commands for example a 2-3 upshift but doesn't see the car in 3rd gear in a certain amount of time. However there is a certain delay that must occur before the code sets. Since your car is shifting the delay between the shifts due to the bad solenoid might not be long enough for the computer to set the code. I would just drive it until it goes and then the car just resorts to second gear (both solenoids off) and will set the code for good. I have the same problem with my car, occasionaly though the shift takes long enough and the code sets locking me into second. I usually just restart the car. This has been going on for like a year though, haven't had a complete failure yet. I should replace them though.

There are no sensors near the solenoids. The PCM does monitor current and voltage of the solenoid and that in turn can generate a code. There isnt a physical sensor detecing physically what the solenoid does it is only monitored via electrical characteristics. Thats why i am trying to find out of anyone ever had one electrically okay (passes the diags) but physically not working.

Wilbraham is east of Springfield, home of Friendlys.

Thanks for taking time to reply.

The computer doesn't monitor the electrical characteristics of the solenoid. It doesn't even know if it engages when it tells it to directly. What does do is look at the input and output speed sensor. It can use these two sensors to determine the gear that the transmission is in, based on the ratio that the two are spinning at. It sets the fault if it commands for example a 2-3 upshift but doesn't see the car in 3rd gear in a certain amount of time. However there is a certain delay that must occur before the code sets. Since your car is shifting the delay between the shifts due to the bad solenoid might not be long enough for the computer to set the code. I would just drive it until it goes and then the car just resorts to second gear (both solenoids off) and will set the code for good. I have the same problem with my car, occasionaly though the shift takes long enough and the code sets locking me into second. I usually just restart the car. This has been going on for like a year though, haven't had a complete failure yet. I should replace them though.

I am curious. How would the pcm be able to generate a solenoid code? Differences between input and output sensors could be caused by more than just the pcm so it couldnt use that as the solenoid bad condition.

I wont admit knowing the 4t80e in depth but i do know for sure pcms will use current draw and voltage to know if an electrical component is running correctly (ala speed sensor, 02 sensor and etc).

Back to my original question .... changed the solenoids tonight and problem solved. So a bad solenoiid does not necessarily generate a code. I will take them apart and would guess i find something physically "but not electrically" wrong. I will also check internal resistance and cuurent draw on a bench to see if it matches factory specs.

Happy Holidays

The input speed sensor spins at the speed of the crank. The output speed sensor spins at the speed of the axel (or perhaps just before the differential, not sure exactly what the output speed sensor is coupled too) Anyways. There will always be a ratio difference between these two, four discrete ratios which are dependent on the gear ratios. So lets say for example in 1st gearis 2:1, 2nd gear is 1.5:1, 3rd gear is 1:1, and 4th gear is .75:1. The car can tell exactly what gear it is in, based on the ratio between these two sensors. If your driving for example in 2nd gear and the PCM commands a shift from 2nd to 3rd but the ratio remains at 1.5:1 for too long a time it will set the solenoid code. Solenoid performance cannot really be measured directly, or easily atleast. Most sensors in a car work by changing the resistance (TPS, MAF) and others work by changing the frequency of a constant voltage AC signal (CAM/crank position, wheel speed sensors). Solenoids are basically a coil of wire which get energized by 12 volts. The only failure detection they could implement easily would be an open circuit, but solenoids don't always fail because of open circuits, as in the case of the shift solenoids for example the houseing breaks down and there is a mechanical failure. So even if they included some method for detecting the open circuit it would only catch half of the problems. Instead solenoids are usually measured indicrectly as in the case with the transmission shifting. A failure is detected by detecting whether or not the desired effect happened...

I am curious. How would the pcm be able to generate a solenoid code? Differences between input and output sensors could be caused by more than just the pcm so it couldnt use that as the solenoid bad condition.

I wont admit knowing the 4t80e in depth but i do know for sure pcms will use current draw and voltage to know if an electrical component is running correctly (ala speed sensor, 02 sensor and etc).

Back to my original question .... changed the solenoids tonight and problem solved. So a bad solenoiid does not necessarily generate a code. I will take them apart and would guess i find something physically "but not electrically" wrong. I will also check internal resistance and cuurent draw on a bench to see if it matches factory specs.

Happy Holidays

have the shift problem and can't get dealer or delco parts house to identify the part number of the ac delco shift solenoid repair kit. They don't know what I am talking about. Please send me Part number nick_colbert@hotmail.com