Transmission not shifting properly?

Tiny
JARED STILES
  • MEMBER
  • 1998 GMC SIERRA
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 233,921 MILES
My truck will start off in first gear when I first start up and go, but it will not shift back down into gears after I've been driving. I can turn it back off restart it and go and it'll start back and first gear but will not go back down in gears. No work has been done to my truck. It just started doing this one day. I changed the first and second solenoid and reverse it did not help. Could be a stuck valve? I was going to pull it back apart and see if that's what it might be but figured I would ask and see if anyone had any ideas.
Sunday, September 11th, 2022 AT 11:33 AM

16 Replies

Tiny
JARED STILES
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And it also will not go into overdrive.
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Sunday, September 11th, 2022 AT 1:47 PM
Tiny
JACOBANDNICKOLAS
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Hi,

Does your vehicle have a transmission cooler? Also, have you tried flushing the transmission? I'm questioning if it is a line pressure issue. Also, have you scanned the computer for diagnostic trouble codes?

I need to know if this is the 4L60E or 4L80E.

Let me know. Also, let me know if it is downshifting into at least second.

Take care,

Joe
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Sunday, September 11th, 2022 AT 6:11 PM
Tiny
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It's 4L60E Transmission and yes it has a cooler and no I haven't hooked it up to a computer yet. I do not believe it's downshifting into second, it will shift up though all gears first when started and drove but will not shift back down. No overdrive or passing gears won't work either.
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Monday, September 12th, 2022 AT 11:43 AM
Tiny
JARED STILES
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I can drive it the way it's running but it starts off slow after it goes though the gears the first time.
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Monday, September 12th, 2022 AT 11:45 AM
Tiny
JARED STILES
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And no, I did not flush it out. I changed the fluid and filter though.
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Monday, September 12th, 2022 AT 12:32 PM
Tiny
JARED STILES
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Sorry, I was at work earlier trying to write back to you it does go into overdrive. As far as I can tell, that's where it stays or stays in third or forth. It's hard to tell on that one been trying to figure it all out. I hope I can get help with it because it's my only car right now. My engine blew up in my wife's car and now we're left with my truck to get us around. I'm going to try and go have it hooked up to a computer in the next couple days.
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Monday, September 12th, 2022 AT 5:20 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Have the computer scanned. I'm hoping it points us in the right direction. Also, it may be a good idea to have the cooler and transmission flushed.

I feel it could be a pressure issue. Here is the thing. You are driving it in limp mode. Limp mode is really only designed to get you off the road to safety in the event of a malfunction. I'm concerned that we are going to damage clutch plates driving it like this. Think about how you would need to feather a clutch on a manual transmission if you started out in 3rd or 4th gear. I just don't want you to cause more damage.

Let me know.

Joe
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Monday, September 12th, 2022 AT 7:02 PM
Tiny
JARED STILES
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I put a new Radiator in it already because it was leaking so that's fine, I'm taking it up tomorrow to see what they're going to charge me to run it on a computer. If I can afford it, I'll have it tested and let you know what it says. Thank you for your help. I'll respond back after I have it run on the computer.
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Tuesday, September 13th, 2022 AT 4:51 PM
Tiny
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Jared,

Let me know what they find. If they are asking a crazy amount to scan it, try having it done at a nationally recognized parts store. Most will do it free of charge.

Although they may not have a scan tool equal to a shop, hopefully, it will pull what we need. Actually, if there is an AutoZone, Advance Auto Parts, or an O'Rielly's nearby, go there first. We may be able to save a buck and not require it to be taken to a shop. I totally understand where you are coming from.

Let me know.

Take care,

Joe
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Tuesday, September 13th, 2022 AT 7:52 PM
Tiny
JARED STILES
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I had it hooked up and it said that shift solenoid B was bad and also said that both Catalytic Converters aren't good, but the guy said that the trucks probably running too lean or too rich and it's causing it to throw off codes for the Catalytic Converters, but I have changed all of the shift solenoids. I have changed the internal wire harness. I've changed the fluid. I've changed the filter. I have changed shift solenoid A and B twice now. So, I have no idea what to do now.
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Thursday, October 13th, 2022 AT 9:02 AM
Tiny
JARED STILES
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There's nothing wrong with solenoids. There's nothing wrong with the wires. It shifts up though all gears when first started and ran but after it goes over 3rd it will not go back down but I can put it in part shut it off. Start it back up and it will start off in first go through all gears just fine but will not go back down. It will only go back down if I shut the truck off the only thing, I can think of is the computer. It's something wrong with it but I was told that it's very unlikely that computers don't just go bad. So, if you can get back to me on what to do next. Thank you. Idk why the computer is saying B solenoid is bad because it's not. Which I already knew because it works when the truck first goes though gears the first time after starting so why would it be saying it's bad when it's not?
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Thursday, October 13th, 2022 AT 9:20 AM
Tiny
JACOBANDNICKOLAS
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If there is a code for shift solenoid B (which is the 2-3) shift solenoid, it shouldn't be causing issues with downshifting. If you have the code that was found, let me know what it is so I can research it for you.

There is a 3-2 downshift solenoid in the transmission as well. That would make more sense to me. See pic below

Let me know.

Joe

See pic below.
Image (Click to make bigger)
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Thursday, October 13th, 2022 AT 6:52 PM
Tiny
JARED STILES
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I was not giving a code all they said was it said it was bad, but I'll go back up to the part store and have them hook it up again and get the code. But I have changed all of the solenoid I have replaced every single one and I replaced the wiring harness. I replaced the filter, I replaced the oil. I will write back in a little while after I stop by the parts store.
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Saturday, October 15th, 2022 AT 1:08 PM
Tiny
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Hi,

I understand. Keep in mind, this can also be caused by mechanical failure in the transmission as well. Once I see the code, I'll have a better idea of what to check.

Take care,

Joe
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Saturday, October 15th, 2022 AT 9:43 PM
Tiny
JARED STILES
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Po758 shift sol.B
Po430 cat system
Po452 E vap
Po420 cat
Those are all the codes for everything. The first one is for the transmission the rest for other things I'm sure u know that though.
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Sunday, October 16th, 2022 AT 9:05 AM
Tiny
JACOBANDNICKOLAS
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Hi,

The solenoid could have been the issue, but the code is specific to a power issue. When the PCM detects a continuous open or short to ground in the 2-3 SS Valve circuit or the 2-3 SS Valve, then DTC P0758 sets.

I attached the diagnostics below. Since you already replaced the solenoid B, it is likely a wiring issue.

Here is my concern. The diagnostics require a scan tool that can communicate with the different modules. I don't know if you have one or have access to one.

Let me know.

Take care and hang in there. I wish I had an easier solution.

Joe

See pics below. Also, I read through the diagnostics and the first thing it suggests is to check the transmission fuse in the interior fuse box. I don't think that is an issue otherwise other things wouldn't be working such as the speedometer. However, I attached it to help you locate the fuse to check.
Images (Click to make bigger)
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Sunday, October 16th, 2022 AT 7:59 PM

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