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Resolved No 3rd and 4th gear automatic transmission

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Dryppical

Proven Member
104
16
Apr 5, 2023
East Helena, Montana
I have an issue where I have no 3rd and 4th. You can hear both of them click when on toggle switches but it only has 1/2. I’m at a complete loss right now. Both solenoids get power but won’t shift past 2nd. I don’t know what the issue is.

When TCU is unplugged it goes into limp mode so I have 3rd so none of this makes sense to me anymore. When I have the TCU plugged in and no toggle switches it doesn’t go in limp mode so it must not be detecting a problem. When I unplugged my power to my toggle switches and watched the lights when they get activated. 1st gear both are on and 2nd is one of them off, then it doesn’t go past that.

Any help is appreciated. I’m at the point where I just want to drop a match into the gas tank
 
Black is ground and red is power. I have power tapped into an ignition on wire. Yellow is for A solenoid and blue is for B solenoid. I have an extra plug and I wired them directly to my toggle switches. Going to test them out here soon and see what happens

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Cracked DSM, you are a godsend. Wiring both wires straight to my spare solenoid plug worked. I now have all 4 gears and they all shift good
Holy shit you were "lucky"!

I'd say continuity test through each connections and check terminals/pins for tightness and corrosion and make sure all grounds are clean!
 
Well, I decided to just snip the wires at each end and run new ones for the A and B solenoid. Took it out for a test drive and still only have 1st and 3rd. Toggle switches I have all gears. It also won’t go into limp mode. I have drove it and turned it off and back on many times and it has yet to go into limp mode. Did higher speed drives at 65 and low speeds at 25. Would turn the car off and on in between to see. I probably did that 30 times to no prevail. I tried my other tcu with the same result. Is my tcu maybe going bad? They smell fine and look good I think. I checked the tcu fuse and it’s good. I even decided to give one of the ground wires its own personal ground. I tested continuity between the ground and the metal where they were grounded and I had continuity. Did that for both ground wires at the tcu. I am very positive that the solenoids are in the right spots one wire is longer than the other so it reaches no issue. I even watched a video to double check and how they took them out is how I put mine in. Decided why not swap the wires and see. Instant limp mode if I do that. I decided to readjust throttle position sensor and that didn’t work. Tested it and it tested good. What am I missing?
 
Well, I decided to just snip the wires at each end and run new ones for the A and B solenoid. Took it out for a test drive and still only have 1st and 3rd. Toggle switches I have all gears. It also won’t go into limp mode. I have drove it and turned it off and back on many times and it has yet to go into limp mode. Did higher speed drives at 65 and low speeds at 25. Would turn the car off and on in between to see. I probably did that 30 times to no prevail. I tried my other tcu with the same result. Is my tcu maybe going bad? They smell fine and look good I think. I checked the tcu fuse and it’s good. I even decided to give one of the ground wires its own personal ground. I tested continuity between the ground and the metal where they were grounded and I had continuity. Did that for both ground wires at the tcu. I am very positive that the solenoids are in the right spots one wire is longer than the other so it reaches no issue. I even watched a video to double check and how they took them out is how I put mine in. Decided why not swap the wires and see. Instant limp mode if I do that. I decided to readjust throttle position sensor and that didn’t work. Tested it and it tested good. What am I missing?
Pressure lines clogged? Maybe measure pressure?
 
I took my spare tcu inside just to look at it again. I think it looks fine, but I also don’t know what I’m looking at. Under different angles of light, you can see these darker streak looking things. Is this bad? If not, any way I can test it to check?

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I did some tcu testing from the fsm. Checking for voltage and whatnot on wires. I have discovered the pressure control solenoid and solenoid A do not receive power. The no power to pressure control solenoid makes sense because it shifts hard into gear. My neutral safety switch is also bad so none of those wires received power. I think I just have to chalk it up to being unlucky and having 2 bad tcus. Maybe I accidentally fried at least one when I forgot to unplug the tcu with the toggle switches hooked up. I suppose I’ll find a known working tcu and toss that in and see what magic it works for me. I added the fsm I followed. Are all 95-99 gsx/gst tcus interchangeable or do I need a specific one?

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Alright fellas, after getting a good used tcu and having the same exact problem as the other 2. I ruled out the tcu. I then decided, why not jump the terminals on the neutral safety switch and I jumped it for L and I had first gear and power on both solenoids. I jumped it for D next and it gets power on both solenoids. The issue when I did this is it kept kicking in and out of gear every couple seconds. Very odd. Anyways, I decided to look at the harness colors for the neutral safety switch and the wires did not match at all. It was the correct connector and not the front main harness one. That one has greens in it and this one did not. Anyways, I depinned it and relocated the wires to their correct spots and bam. Now it shifts. I don't know if this is a different neutral safety switch from a different car or what but none of the wires lined up with each other. I spent 3 months chasing this problem and spent hundreds of hours trying to figure it out and a whole lot more researching. My old solenoids were probably good still LOL. Thank you everyone for the help and advice you guys gave me
 
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