Okay, I feel kind of like a fool now. My sister’s Grand Am has been having a shift flutter issue (between third and fourth, around 40 mph it would shift rapidly back and forth until you either forced a downshift or reached 50-55 mph) for a while now. I read a lot about it online, and all signs and the experiences of others pointed to a bad shift solenoid or pressure control solenoid. I wanted to correct the issue before it caused any damage to the transmission. I removed the transmission from the car and replaced both shift solenoids, the torque converter clutch solenoid, the pressure control solenoid, and the manifold pressure switch with new ACDelco parts. I figured I may as well replace them all while the trans was apart. I also replaced the filter and fluid, of course. I got everything back together, and now the transmission slips in reverse and overdrive no longer works. Fluid level is full according to the method of pulling the level check fill plug while hot, idling in park. I used Valvoline Maxlife fluid, which meets Dexron VI specs according to the product label. I have double and triple checked everything and can’t even fathom what I could have done to cause these new symptoms to crop up. Any ideas?
Another oddity I have noticed: the transmission works the same regardless of what range the shifter is in. If you shift to first, it will still shift through second and third normally. Shifting from drive to first will not force a downshift.
I’ll have to assume that along with double-checking the fluid level and all of that you also double checked all of the electrical connectors? Perhaps including a good blast of electronics cleaner and inspection and all? That whole line of 4TxxE transmissions are hyper-sensitive to the electronics bugs. The thing about the shifter range makes me suspicious of something as simple as that.
“Overdrive” gets used differently by different people (despite it’s fairly precise technical meaning). So are you saying it won’t shift into fourth?
Has it thrown any codes at you? Do note that these will also throw codes that won’t set an engine light and require a Tech II. Unfortunately, your best route would be to get your hands on one of those. But I would certainly go over all of the basic electrical connectors, and even include a thorough check of the basic main power connectors, including ground.
The only code it has thrown had to do with the crankshaft position sensor (P0336 I think). The check engine light was on right away. I could not find my ELM327 dongle, so I drove the car to a friend’s shop, where it refused to restart. He pulled that code and I found that the harness for the crank position sensor had come loose, so no surprises there.
By “overdrive” I mean fourth gear. It has not shifted into fourth or locked the torque converter clutch since reassembly. As for the slip in reverse, it may have been there before and gone unnoticed. I haven’t driven the car in years and only ridden in it with my sister to demonstrate the shift flutter. She backs up much more slowly and cautiously than I do, so it may have been there but never existed for her.
As for electrical connectors, I have only checked to ensure they are all plugged in, with the exception of the range switch. I removed and inspected the range switch (parts stores call it a “neutral safety switch”, but it has two harnesses and 11 wires going to it, which leads me to believe it does more than serve as a neutral safety switch) and checked the wiring for it. The anomaly of it treating all gears as drive (or “3” in this car) has me very suspicious that the range switch is bad. The action of the switch feels loose and sloppy when you use your hand to actuate it, so removing it to separate the case may have done it in. However, I’m having trouble justifying spending $76 on a “part dart” to throw at it and hope for the best.
Well, you did just have the entire transmission out. That’s pretty major surgery. If you have a friend with access to a Tech II scanner, that’s the easiest route. But personally, I would just go over every electrical connector again - even ones not on the transmission. You can probably also find specs online to find out what the range switch (aka neutral-safety or PRNDL) is actually doing electronically.
I also meant to mention that I once had a problematic 4T65E and used Valvoline Maxlife in the midst of fluid changing and such. I though it made things worse. I know that they claim a wide range of specs - but the specs themselves are just ranges, and that’s the problem. I seriously doubt it would explain these problems, but just thought I’d mention it.
Well, I tried replacing the range switch with a used one, which made no difference at all. I also took the car to a couple different transmission shops. The first one pretty much told me to take a flying leap (“oh, we will have to pull the trans and take everything apart, which will cost at least three grand since SOMEONE ELSE was in there and you never know what could have happened” For the record, a five year old could have done all the internal work I did unassisted and with minimal guidance). The second one test drove and scanned the car and declared the transmission dead (unable to maintain sufficient pressure to shift properly; he said the forward gears were also slipping, which I could barely detect). They suggested that the new sensors and solenoids, and possibly to a much lesser degree, the new fluid, could have aggravated an already marginal transmission, and that valve body wear is generally to blame for the shift flutter. I located a used transmission today with 45k miles for $150, so I snapped it up before someone else could and am hoping to never have to remove the transmission from this car again.
I know this is an old thread but im having the exact same problem with my 2000 where if you get it to 4th gear then let off, brake then hit the gas it’s rapid shifting from whatever gear but it doesn’t affect the tachometer but reduces power. It will still accelerate, usually if i let off the gas for about a second then reapply it, the transmission will then shift normally.
I have been also reading and someone with similar but not the same issues was suggested to replace the “Transmission Fluid Pressure switch” im not entirely sure if that’s the same as the pressure solenoid you replaced but ill probably have no choice but to give that a go. I don’t have the option to do it myself so seeing if my mechanic is willing to replace it. But that would be like $200 of a guessing game to see if its the issue.
Another thing i noticed the problem tends to mostly happen when the weather is hot, maybe humidity is a factor. Something electrical maybe is getting corroded? I don’t know enough of the transmission in this car to really know. Could this issue not be actual transmission but something else? Certainly seems like it if you tore into the transmission but ended up making it worse.
Could be caused by quite a few different problems. Suggest to ask a good, well-recommended local transmission shop to assess the situation. Usually there is one such shop in an area where all the local mechanics take their cars, so ask the mechanics at the auto repair shops who they use. Transmission diagnosis and repair requires a lot of expertise. You don’t want someone who’s just learning on their own working on your transmission, like you don’t want a beginner surgeon working by himself doing your operation.
Auto trans require a lot of force to effect the shifts so they use a sort of hydraulic computer. The brains of this gadget has both electric actuated solenoids, and pressure actuated valves using springs and one-way check-balls. It also has a sort of wiring matrix (not using actual wires, fluid filled tubes) to route the fluid pressures where they need to go. All that stuff has various seals that can harden & fail, part of the transmission’s valve body. Sometimes just replacing the fluid with fresh stuff will help b/c fresh fluid contains fresh seal conditioning chemicals.