Transmission not shifting

Tiny
ERNEST23
  • MEMBER
  • 1993 CHEVROLET SILVERADO
  • 4.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 302,951 MILES
Won't shift up, revs super high, speedometer not working until I hit a bump. Changed these items: new A/C system(entire), brake system, battery, cooling system, sensors: map, TPS, knock, coolants, vacuum lines, cap, and rotor, plugs and cables, belt, valve covers. Can't give up now. I know with the mileage it's already being stretched far.
Saturday, October 2nd, 2021 AT 6:03 PM

11 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Did this issue just start, or has it been having shifting issues for some time now?

If the speedometer and shifting issue started at the same time, then you more than likely have the electronically shifted transmission. If this is the case, then the ECM/TCM uses the speed sensor for shifting.

However, the revving high makes me think we have internal issues because normally a speed sensor issue just causes it to shift hard or incorrectly.

The high RPMs point to a pressure issue or fluid issue so let's start there. Check the fluid and change it if it is not clean or full.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

I am attaching the info about the speedometer as well but again, let's start with the fluid and go from there because this speedometer issue may have caused the overall failure, so we need to go backwards for now.

Thanks
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Sunday, October 3rd, 2021 AT 7:27 AM
Tiny
ERNEST23
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Forgot to mention in my question that I did change the speed sensor at the back end if the transmission. The o ring was wasted away. It was giving me a code 24. That's why I changed it. The transmission would shift up only after stomping the gas heavy but still no speedometer. I now have codes 16, 24, 72, 73. Ii can drop it into low first but I know it's unhealthy. Will check fluids after I operate it today. Thank you.
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Sunday, October 3rd, 2021 AT 9:40 AM
Tiny
KASEKENNY
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Okay. With all these codes I would suggest starting with the 73 code.

The other codes may still be there from the speed sensor issue and 73 is for the control solenoid so that is a good one to start.

The fact that you can shift it down to low and it works points to a solenoid issue so that is the best place to start.

Please run through all this after you check the fluid, and we can go from there.

Thanks
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Sunday, October 3rd, 2021 AT 6:06 PM
Tiny
ERNEST23
  • MEMBER
  • 6 POSTS
Checked fluid three different times throughout the day. Still full. Am I understanding that to check solenoid I need to drop pan? Further information: the transmission has been shifting hard from first shift for over five years (stepdad truck). I only have multimeter and test light. I will have time Wednesday to begin the work schedule for testing using the information you sent me. Thank you for your patience.
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Tuesday, October 5th, 2021 AT 3:01 AM
Tiny
KASEKENNY
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Yes, that is correct. With that information dropping the pan is probably the best thing just to check for metal and find out what is in the pan.

Also, if you test the solenoid as shown in the testing for code 73 then that would be good to do at the same time.

However, just want to make sure you fixed the speed sensor but still have code 24 or is that code gone?

Thanks
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Tuesday, October 5th, 2021 AT 7:27 AM
Tiny
ERNEST23
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Update: after I changed the sensor, I got back the codes I mentioned earlier. Today I had disconnected the battery and was tinkering with the fusible links harness. One by one taking each off to check if they were loose or dirty, then cleaning each terminal with a metal scrub and replacing. Also did the same to the negative cable where it grounds to the top of the engine. When I went to work the transmission worked better. Odd, but the ABS light came on while I was turning and transmission slipped during that action (did that three times before I had the non-shifting issue), now it is only giving me code 72. Still going to run through the tests you sent me. Will let you know what I find.
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Tuesday, October 5th, 2021 AT 11:38 PM
Tiny
KASEKENNY
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That is interesting. The fact that you have the brake lights and ABS tells me this may be related to that system as this code 72 applies to the PCM or ABS, so it depends on which module the code was retrieved from to know which test to follow.

However, the fact that you have a speedometer issue I would start with the vehicle speed sensor code.

Please run through this test and let us know what you find. Thanks
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Wednesday, October 6th, 2021 AT 2:25 PM
Tiny
ERNEST23
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So, I found this. I cleaned up the wires, wrapped them in electrical tape, and crossed my fingers. It worked. No codes are coming back. I don't know why I didn't see that before.
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Friday, October 8th, 2021 AT 7:46 AM
Tiny
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Oh my. Yes. That will do it. If that doesn't work, then you may have to cut those wires out and put a new connector and solder the wires on.

However, if you protect them pretty well, it should be fine.

Thanks for coming back and showing us that.
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Friday, October 8th, 2021 AT 11:32 AM
Tiny
ERNEST23
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I did notice a lot of oil under the engine. But no oil coming from valve gaskets. Engine is doing the Chevy tick like crazy.
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Friday, October 8th, 2021 AT 11:35 AM
Tiny
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Okay. Then we need to make sure the engine remains full of oil to hope that tick doesn't get worse. Normally it is only a matter of time with it but keeping it full will hold that off as long as possible.
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Friday, October 8th, 2021 AT 12:00 PM

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