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Old 07-28-2022, 06:03 PM   #1
Keblar
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2002 SL2
Default Troubleshooting TAAT Hard Shift

I've been scouring the archives for troubleshooting tips on transmission hard shifting. It's never had what I'd call reverse "slam" but reverse has been finicky and a little hard for years. As long as you were patient and held the brake until actually shifted though, it was fine.

Recently though it began hard shifting in all ranges. With a P0706 code (transmission range sensor). Downshift was even rougher. Even violent sometimes. Hard enough up and down to stop driving for fear of damage. Plus now reverse definitely has a "slam".

I cleared the PCM - No change. Did a fluid and filter change with Valvoline Blue (Hence my TranSynd and TES 295 questions last week). It was dark and definitely needed it, but not burnt or black - still, no change.

I ran the Wolfman Reverse Slam Fix, although without any additive, not expecting it to actually do anything. BUT, while the upshift and reverse are still hard, the downshift jerk is almost completely gone. I may actually try some seafoam trans tune and run the fix again since I plan on refilling with full synth anyway to see if the "fix" helps anything else. I doubt it but...

I still have to confirm the Transmission range sensor switch too, but I haven't seen any other transmission codes since resetting the PCM.

Still it IS seeming more and more like I'll need a rebuilt valve body. Going to keep looking to see if I'm missing any other possibilities.
...
2002 SL2 335k + Miles
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Old 07-30-2022, 07:48 PM   #2
Keblar
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Default Re: Troubleshooting TAAT Hard Shift

I tested the Transmission Range Sensor / Switch as shown in the RichPin video and got no continuity tone when shifted into drive.

I loosened up the bolts to see if i could adjust it, but still got zero tone throughout the full range of adjustment. This means the switch is just bad, right? Am I missing anything? If i understand correctly, even an electrical issue wouldn't matter in this case. The continuity test just indicates that the internal switch isn't closing, and electrical connections play no part in this. I think I read someplace that the test can even be done without the key turned on.

Edit: Fetchitfido provided the FSM for the switch replacement procedure in THIS POST and it doesn't even indicate to "Connect the transaxle range switch harness connectors" until after the range has been set testing continuity on the new switch. In which case, I'm ordering a new switch.
...
2002 SL2 335k + Miles

Last edited by Keblar; 07-30-2022 at 07:57 PM. Reason: New info
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Old 07-30-2022, 11:55 PM   #3
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Default Re: Troubleshooting TAAT Hard Shift

I'm not sure which switch terminals you are using for the adjustment, but if you use the correct ones there will be continuity (tone) in only P and N; can't use any forward gear or R.
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Old 07-31-2022, 10:27 AM   #4
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Default Re: Troubleshooting TAAT Hard Shift

Quote:
Originally Posted by billr View Post
I'm not sure which switch terminals you are using for the adjustment, but if you use the correct ones there will be continuity (tone) in only P and N; can't use any forward gear or R.
From the FSM:
"Place the transaxle in Drive (D). Use an ohmmeter or continuity tester to check for continuity across terminals on the selector switch. Rotate the transaxle range switch from the left fender towards the engine until continuity is achieved."

This uses the 2 terminals from the single plug on the very top, not from the connectors on the side. I assume The P and N test you're referring to are for the Neutral Safety Switch portion. Not sure since I've thankfully never had to test that. [knock, knock]
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Old 07-31-2022, 01:38 PM   #5
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Default Re: Troubleshooting TAAT Hard Shift

Yeah, my mistake on the P/N vs D, sorry. I'm old and it was late at night, that's my excuse and I'm sticking with it!

That top "test" terminal is separate from the range function, and has a quite narrow range of contact compared to the range switch. Point is, The range function may still be OK, and can be easily checked using live-data. I would not rush to change that switch just yet. On my gen1 the switch was easy to disassemble, yours may be the same and you could peek inside to inspect or verify how it operates.

I don't think the range switch will cause harsh shifts, anyway. That is controlled by the "fill time" for the clutches and line-pressure (LP). Both can be checked using live-data and a pressure gauge.

Have you checked the LP fuse and solenoid? Have you done the "fuse pull" test for LP?
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Old 07-31-2022, 04:14 PM   #6
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Default Re: Troubleshooting TAAT Hard Shift

The LP Fuse checks out, but I haven't done the "fuse out" test (i over looked that procedure), or tested the solenoid. Given the 0706 code I wasn't going to open the valve body cover until I checked out the switch 1st. When I couldn't get continuity I assumed it was bad didn't go any further.

I read that the sweet spot for the D test was small, so slid the switch pretty slowly and left a little friction on the bolts when checking/adjusting. It's not impossible that i missed it, but man, if the adjustment needed is THAT fine, I'm not sure anyone ever manages.

I haven't been able to find my scanning dongle anyway, and the switch is ordered. At the risk of wasting $60 on the part, I'll probably have to wait until the new one is installed and move on to solenoids and line pressure afterwards if it isn't solved. I'll need a line pressure gauge and possibly new scanning tool before then anyway if I can't locate it.

I am a little confused though, is the line pressure solenoid separate from the other solenoids on the valve body? Would it be included in a rebuilt body, or would it have to be ruled out / replaced on its own regardless?
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Old 07-31-2022, 05:03 PM   #7
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Default Re: Troubleshooting TAAT Hard Shift

The LP solenoid is on the VB, and is identical to the other four solenoids there. You can check resistance of all those solenoids from outside the trans, at the 10-pin connector on top of the VB cover.

Yes, that test contact for adjusting the range switch is very fussy; I'm guessing it makes contact over only about 1 deg of rotation; while the other contacts "make" over 5-10 deg. I found that once I had the switch adjusted for contact in D, it would not make contact again every time I moved it out of D and back to D
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Old 07-31-2022, 09:41 PM   #8
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Default Re: Troubleshooting TAAT Hard Shift

Well, thanks for the inspiration to double check the range sensor - it took 5 more equally diligent tries, but I was surprised and very annoyed to find a spot that got continuity. I AM now getting a persistent P0708 code though. Reverse slam is still present - shift into D is perfectly smooth - but up-shifts are hard, and down-shifts are worse again.

I'll have to try and re-adjust later this week to see if i can get 0708 to go away - maybe clear the PCM again and start over. [I just realized, is a relearn required whenever the PCM is reset?]

The switch MAY still be bad, but I can't get good transmission data on Torque pro (I did finally find the dongle) to verify proper positioning. Seems like there used to be a plugin for GM data on Torque pro, but all the links I find are dead and it's not in the list of available makes anymore. I'm not even sure Torque Pro is supported anymore, it may be a zombie app. I'll try to find an alternative in the next few days.

I'll test solenoids now that I know I need to, and can get to it without removing the cover (something else I overlooked in the sea of info, thanks Bill). I'll be using the fireman video to identify pins, but it could be a few days before I'm able to get to that.

Thanks!
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Old 08-10-2022, 05:59 PM   #9
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Default Re: Troubleshooting TAAT Hard Shift

your line pressure solenoid in the valve body is faulty or your electrical connector on top of the transaxle is saturated with ATF. Had both issues over the course of 22 years and 526,000km. See youtube for coil resistance testing of the line pressure solenoid. Also see this video for faulty mechanical symptoms of the solenoids. https://www.youtube.com/shorts/lj9pKsT8lDg
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Old 08-13-2022, 02:35 PM   #10
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Default Re: Troubleshooting TAAT Hard Shift

Finally found a weather cooperative time to test the solenoids.

Using the Layout

KJHGF
EDCBA

Resistances were:

AB - 4.7 CD - 4.8 EK - 4.9 FG - 5.0 HJ - 5.0

I believe these are 3rd, 4th, Line Pressure, TCC, and 2nd respectively.

I did two solid passes. Some of these varied by .1 Ohms on a few tries, but on retests they all checked out otherwise.

My understanding then is that since these are all within 1.0 Ohms of each other, they all check out as good/within spec.

I still have not installed the new range switch yet, but I do have it on hand.

Incidentally, the harness was dirty on the wire side (as to be expected), but was not oil or fluid soaked. The connectors looked pristine with no charring present.
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Old 08-13-2022, 03:59 PM   #11
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Default Re: Troubleshooting TAAT Hard Shift

Get on to that fuse-pull test for LP. It is reasonably cheap and easy to do, and could be quite revealing.
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Old 08-14-2022, 12:15 AM   #12
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Default Re: Troubleshooting TAAT Hard Shift

After reviewing at this point, it seem like the next step in troubleshooting, or at least the next cause to eliminate, is a loose input shaft nut. That at least seems to be a relatively cheap, but incredibly labor intensive fix.

I'm also curious, since the clearance on the side cover, along with the mounting shaft makes the input and output shaft nut replacement (or re-torque) pretty difficult: Has anyone determined if it's possible to CHECK the input and output shaft status before completely removing the cover? IS there enough clearance space to check 1st without having to relieve the lower engine bracket pressure, etc, and actually removing the cover since that seems to require the most effort?

Quote:
Originally Posted by billr View Post
Get on to that fuse-pull test for LP. It is reasonably cheap and easy to do, and could be quite revealing.
Could you elaborate on you version of the fuse test. The only one i can find is the one that uses a pressure gauge at the sensor port. Is that the test you're referring to?
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Old 08-14-2022, 01:42 PM   #13
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Default Re: Troubleshooting TAAT Hard Shift

Yes, you remove the TFT sensor, the smaller one near/under the spin-on trans filter, and install the gauge in that port. It is common 1/8" National Pipe threads, so any adapter fittings needed are easy to find locally. You will need a 300 psi gauge.

With the engine idling in P or N, the gauge should read about 60-70 psi. Then, when you pull the LP fuse, the LP should shoot up to about 270 psi (still idling in P/N).

If these pressures are about right, then make provision to connect the gauge with a hose long enough to reach into the cabin and observe LP as you drive. You can compare LP on the gauge to what is shown as "commanded LP" in live-data.

Any small-diameter reinforced hose, like common air-line hose, will be fine for 300 psi. Just use air-line barbed fittings and small hose clamps. I would not use air-line quick-disconnect fittings, though. They tend to leak slightly, no big deal with air, but could be a mess with ATF...
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