4l65e behinc LS3-> Downshifting early
Thread Starter
Teching In
Joined: Jul 2020
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4l65e behinc LS3-> Downshifting early Actually, what happens is I start driving, it shifts what seems normal, but as I let up on the foot feed, it downshifts, seemingly to low. The speed limit in our neighborhood is 20. When this happens, the engine rpm at 20 mph is 2000.
I definitely am not driving for now.
I read a bit on downshift solenoid, and the symptoms don't seem to align with that.
I should also mention that this trans has been upgraded from a 2006 design to a 2009 Silverado design. Required changeout of the valve body, and a few other things. It would be natural to think something they did is problematic. It could also be, I suppose, an issue in the ECM programming. But if it were that, I would think it would have exhibited this immediately when I picked the car up. That being said, I've only put a little over 100 miles on it since then (It is a 61 Chevy...not a daily driver). .
I'm not sure if I need to take it to a tuner or a trans shop.
Any thoughts?
I definitely am not driving for now.
I read a bit on downshift solenoid, and the symptoms don't seem to align with that.
I should also mention that this trans has been upgraded from a 2006 design to a 2009 Silverado design. Required changeout of the valve body, and a few other things. It would be natural to think something they did is problematic. It could also be, I suppose, an issue in the ECM programming. But if it were that, I would think it would have exhibited this immediately when I picked the car up. That being said, I've only put a little over 100 miles on it since then (It is a 61 Chevy...not a daily driver). .
I'm not sure if I need to take it to a tuner or a trans shop.
Any thoughts?
TECH Junkie
Joined: Jun 2008
Posts: 3,194
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From: Nitro Alley
You should look for DTCs that are current or in history.
You should look at the tune; regarding the shift tables.
This unit does not have a "down-shift" solenoid...
The part closest to being referred to as such, would be the 3-2 Control-Valve Solenoid (and a 2009 and up unit does not have one).
You should look at the tune; regarding the shift tables.
This unit does not have a "down-shift" solenoid...
The part closest to being referred to as such, would be the 3-2 Control-Valve Solenoid (and a 2009 and up unit does not have one).
Thread Starter
Teching In
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Thanks for the input.
The only codes I've seen were in fact recent: pending P0300, then with a few miles after that it changed P0303.
I pulled the plug in cylinder 3, and swapped out with 5. Then in the next 25 miles I got a P0305.
So I have just put in new plugs, and wires. Didn't help the trans issue. I will say that the trans issue got worse pretty much in synch with the P0300 code.
I'm thinking maybe the ECM should have a fresh install of config. I'm not sure if that is possible while on the car.
The only codes I've seen were in fact recent: pending P0300, then with a few miles after that it changed P0303.
I pulled the plug in cylinder 3, and swapped out with 5. Then in the next 25 miles I got a P0305.
So I have just put in new plugs, and wires. Didn't help the trans issue. I will say that the trans issue got worse pretty much in synch with the P0300 code.
I'm thinking maybe the ECM should have a fresh install of config. I'm not sure if that is possible while on the car.
TECH Enthusiast
Joined: Sep 2005
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I spoke with the folks that programed the PCM and TCM late today.
During the efforts by the folks that upgraded my trans to the newer model, they changed the TCM. I was thinking that they had update the VIN. But...maybe they didn't.
He suggested that I check the VIN registration on the PCM and TCM and see if they match. I only have an inexpensive BAFX Bluetooth Scanner for Android. I don't think I can see that with this scaanner.
Any suggestions on if there is a relatively inexpensive option to find that info? (I'm afraid to drive it a distance. Not sure how the trans will act as I drive it over 20mph at the moment.)
During the efforts by the folks that upgraded my trans to the newer model, they changed the TCM. I was thinking that they had update the VIN. But...maybe they didn't.
He suggested that I check the VIN registration on the PCM and TCM and see if they match. I only have an inexpensive BAFX Bluetooth Scanner for Android. I don't think I can see that with this scaanner.
Any suggestions on if there is a relatively inexpensive option to find that info? (I'm afraid to drive it a distance. Not sure how the trans will act as I drive it over 20mph at the moment.)
Thread Starter
Teching In
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Latest update...my original idea of what was happening was wrong. The aftermarket cruise control has a usb diagnostics port which would show me what gear the car is in. So I hooked that up to a laptop and took a drive.
What is happening is it is not downshifting. When it shifts to third gear, it acts like it is slipping, and the RPMs go up. If I accellrate to around 4000 rpm, it seems to be pulling, and shifts to 4th gear. In that gear it acts like it is going to do the same thing. I didn't want to push it any further.
My inexpensive scan tool does not read TCM codes. I spoke with the tech guy at PSI conversions. He said that if the 2 purple wires in there harness is not seeing the right voltage, it could possibly cause this symptom. It needs to see 0 volts when brake not pushed, and 12V when it is pushed. It'll be an effort to get to those wires and check that. The other thing he said is I need to be sure that the new TCM the other shop put in is VIN matched with the VIN on the PCM. It is not throwing codes around that, and he indicated it doesn't always throw the mismatch code.
In the meantime, I am researching to see if I can identify a scan tool that won't break the bank. I found this one, which indicates it will read TCM codes, but I'm not sure it will read VIN on both PCM and ECM to be sure they are matched. It is a read only tool, not too expensive at $129. Looks like I'd have to spend several hundred dollars for a tool that would allow me to make changes. Given I'm not experienced with that, probably better if I can just verify what is wrong then seek a shop that can handle the needs.
If anyone has more thoughts now, will be happy to hear them. Also on recommendations on a scan tool.
What is happening is it is not downshifting. When it shifts to third gear, it acts like it is slipping, and the RPMs go up. If I accellrate to around 4000 rpm, it seems to be pulling, and shifts to 4th gear. In that gear it acts like it is going to do the same thing. I didn't want to push it any further.
My inexpensive scan tool does not read TCM codes. I spoke with the tech guy at PSI conversions. He said that if the 2 purple wires in there harness is not seeing the right voltage, it could possibly cause this symptom. It needs to see 0 volts when brake not pushed, and 12V when it is pushed. It'll be an effort to get to those wires and check that. The other thing he said is I need to be sure that the new TCM the other shop put in is VIN matched with the VIN on the PCM. It is not throwing codes around that, and he indicated it doesn't always throw the mismatch code.
In the meantime, I am researching to see if I can identify a scan tool that won't break the bank. I found this one, which indicates it will read TCM codes, but I'm not sure it will read VIN on both PCM and ECM to be sure they are matched. It is a read only tool, not too expensive at $129. Looks like I'd have to spend several hundred dollars for a tool that would allow me to make changes. Given I'm not experienced with that, probably better if I can just verify what is wrong then seek a shop that can handle the needs.
If anyone has more thoughts now, will be happy to hear them. Also on recommendations on a scan tool.