Automatic 4L60E erratic shifting problems
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From: MN
Automatic 4L60E erratic shifting problems First off, let me apologize if this thread is redundant and I just did not do enough due diligence to find it previously posted. I recently acquired a 2004 GMC Envoy with a 4.2L Inline 6 mounted to 4L60E 3-speed with overdrive with 224000 miles on the clock. The engine runs fine, nice and strong. The transmission goes into gear nice and soft and accelerates off the line strongly. No slipping no fuss. The problem I'm having is as I get to highway speed and am cruising between 50 to 70 mph The transmission will randomly shift between overdrive and third every 10 seconds or so. It seems to do it more when I put it into cruise control. Below 50 and above 70 it really seems to buckle down and stay in gear but within that range it's erratic shifting from below 2000 rpm to almost 2300, back and forth and back and forth. The fluid is a nice pretty red color. Looks like it was flushed recently. No CEL, No burning smells. No slipping no banging. Everything else is fine with it. I'm quite certain it's not the clutch pack because it engages solidly. I keep getting conflicting answers regarding solenoids-pressure solenoid, shift solenoid a, shift solenoid b, etc. I am a fairly adept individual when it comes to cars but have very little experience with inside of transmissions. I have found kits online that come with all of the solenoids and valves to rebuild the valve body online and have thought about replacing them all instead of trying to test resistance and troubleshoot individual solenoids. Any point in the best direction to start would be extremely helpful. I appreciate you all, thank you!
Last edited by GS421; Jul 1, 2023 at 04:15 AM.
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From: BERWICK PA
Sounds to me more like you have hit the speed in which enough throttle pressure is required at that speed to match the converter unlock kickdown throttle position. You might look at changing that throttle parameter in tune. I had a friend towing a small trailer run into that at 70mph he would go in and out in and out of lockup and it was commanded, just at that perfect storm point, He changed the values for lockup verse tps verse speed and fix that.
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From: BERWICK PA
No , I mean sure if it was not doing this and just started this could be dirty maf something like that, But what I actually meant was nothing may be wrong could be you just found that perfect spot speed vrse tps vrse maf vrse rpm where lockup is off and on off and on since you have no codes or other issues.
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No , I mean sure if it was not doing this and just started this could be dirty maf something like that, But what I actually meant was nothing may be wrong could be you just found that perfect spot speed vrse tps vrse maf vrse rpm where lockup is off and on off and on since you have no codes or other issues.
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From: BERWICK PA
Actually many over the years have complained about "hunting" is how the refer of the 4l60e through the years.
IMO you are dealing with one of the following.
1-Its the sweet spot I mentioned and lockup is hunting in and out. - Cure change lockup parameters in the speed cruising zone.
2- Dirty MAF TPS out of range but not so much as to set a code.
3 - random misfire could be related to above causing converter to lock unlock randomly
I do not think it is a solenoid . converter or other mech issue . Further study with scanner or tuning software / data logger may help track it down further.
IMO you are dealing with one of the following.
1-Its the sweet spot I mentioned and lockup is hunting in and out. - Cure change lockup parameters in the speed cruising zone.
2- Dirty MAF TPS out of range but not so much as to set a code.
3 - random misfire could be related to above causing converter to lock unlock randomly
I do not think it is a solenoid . converter or other mech issue . Further study with scanner or tuning software / data logger may help track it down further.
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From: Roxana, IL
I feel your concern too. I drive a 2004 Trailblazer 4.2L 4L60E w/ 342 gears. At those highway speeds I do encounter a TCC unlock/lock. At 70 MPH i cruise at 2000 RPM and when it unlocks it goes to approximately 2300 RPM just like you describe.
1st drive as normal and check engine RPM. Then pull it to 3rd and note the RPM difference. You should be at approximately 2900 RPM in 3rd at 70 MPH. So if you are cruising in OD @ 70 MPH & 2000 RPM and when it makes the downshift/TCC unlock change. You should match the 70MPH in 3rd 2900 RPM, if it is actually going to 3rd. If it does not match, you have just proved that it is a TCC unlock condition.
For your sake please note if you are going slightly up hill or down hill. Also note if it is more sensitive if you have more passengers or loads.
To me what you describe is normal operation for the Envoy/Trailblazer to do. It can be more noticeable as the engine wears and creates less vacuum. The TCC is directly effected by the engine vacuum and the MAP sensor. MAP sensor senses slight load changes and the PCM compensates by unlocking TCC to keep it in the MPH range you are driving. Cruise control is very sensitive in the Envoy/Traiblazer line and you will feel the TCC unlock more than just with your foot.
1st drive as normal and check engine RPM. Then pull it to 3rd and note the RPM difference. You should be at approximately 2900 RPM in 3rd at 70 MPH. So if you are cruising in OD @ 70 MPH & 2000 RPM and when it makes the downshift/TCC unlock change. You should match the 70MPH in 3rd 2900 RPM, if it is actually going to 3rd. If it does not match, you have just proved that it is a TCC unlock condition.
For your sake please note if you are going slightly up hill or down hill. Also note if it is more sensitive if you have more passengers or loads.
To me what you describe is normal operation for the Envoy/Trailblazer to do. It can be more noticeable as the engine wears and creates less vacuum. The TCC is directly effected by the engine vacuum and the MAP sensor. MAP sensor senses slight load changes and the PCM compensates by unlocking TCC to keep it in the MPH range you are driving. Cruise control is very sensitive in the Envoy/Traiblazer line and you will feel the TCC unlock more than just with your foot.
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From: MN
Yeah that makes a lot of sense because it does not drop all the way down to the same RPMs. I would be in third gear and going at 70 mph. It's definitely acting like it's anticipating the gear shift. So I guess my question is, does this cause the engine or transmission any problems? Or is this just something to be used to while I'm driving this truck?
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From: Roxana, IL
Yeah that makes a lot of sense because it does not drop all the way down to the same RPMs. I would be in third gear and going at 70 mph. It's definitely acting like it's anticipating the gear shift. So I guess my question is, does this cause the engine or transmission any problems? Or is this just something to be used to while I'm driving this truck?
The only way I can explain it is: Pretend I have never seen or heard of a Banana. Now tell me what a Banana tastes like.
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2 different veteran transmission guy's have stated that what you are describing is normal. So with that said. Without any raw data from a scan tool or specifics on RPM's. All that we can do is speculate about this. I tried to paint a word picture of the exact scenario needed for us to further diagnose. We need specifics to diagnose something over a forum.
The only way I can explain it is: Pretend I have never seen or heard of a Banana. Now tell me what a Banana tastes like.
The only way I can explain it is: Pretend I have never seen or heard of a Banana. Now tell me what a Banana tastes like.
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From: Roxana, IL
I will respond in the body of this quote.
Overall the TCC hunting may not be able to be fixed without an engine. As I said before the MAP sensor is looking at manifold vacuum changes and as it sees the vacuum goes lower (load on engine) with the gear it unlocks TCC. Then when the vacuum rises because of the lesser load it locks. Then it repeats this cycle over and over and over. AKA TCC hunting. You could confirm this either with a scan tool or a physical vacuum gauge. Watch the vacuum while it hunts in & out of lock up. We used to have that issue with bad vacuum switches on the S10 and Chevy Vans. A new MAP sensor might change things there but probably will not fix the shudder issue.
I had good results back in the day fixing TCC shudder with the TransGo SK4L60E kit and just replacing the the TCC valve. I used the PR springs and that valve. 80% plus fix rate. We used to sell the fix for $600 if it didn't work the trans job would be $2150.00. I helped a friend fix a 1998 Bravada 4.3L with the TCC shudder about a year ago with that kit. If you shop wisely they are on eBay for under $40. Then you would want VB gaskets, fluid and filter too.
I would like to preface with exactly everything you said tracks with the extensive research I've done, that the issue is a TC engaging and disengaging. I understand and that is what I was trying to convey. That said-When I am driving along at highway speeds, between 50-70 mph, the rpms shift from 2000-2300 every 10 seconds or so. This is on flat ground? I've noticed when I am using the cruise control function it happens far more frequently. As I stated my own vehicle does it more frequently when on cruise. It just does not do it on flat ground, only when it goes slightly uphill, definitely not every 10 seconds or so. I have no code being thrown and there is no CEL illuminated on the dash. It won't because SES light is geared toward Main emission codes. Not always transmission codes. The fluid level is full and has a nice clear cherry Kool Aid red color to it with no burn smell to it, however I do not know the last time it was changed (looks and smells recent). That's because the PO may have had it flushed in an attempt to fix it or sell it. I'm not a mechanic, but am fairly mechanically adept. I have not noticed any tranny (can you still say that these days?) slip.Yes you can say that! I got nicknamed Transman 30 years ago because people just couldn't remember my given name. I added the "Z" because of the negative connotation 20 years ago... Now I don't care! Going in and out of gear is smooth, with the only real tell being the drop or raise in rpm. The only rough shifting I have experienced is when I've had my foot completely on the floor , starting from a dead stop on a highway on ramp, being forced to make a gap in heavy traffic. But even that is mild. In my efforts to troubleshoot I have taken the time to downshift into 3rd at highway speeds. I noticed when I drop it into third the rpm remains constant, in the 2900 rpm range you've stated. It's only when in OD that the shifting is erratic, but does NOT reach the 2900 rpm experienced in 3rd gear. Merely the roughly 2300 rpm as I had described.These 2 statements confirm that it is not a 4-3 downshift but merely a TCC unlock & lock. I will also confirm that when TCC unlocks and then locks it can feel like a "downshift" and a "upshift" because it kind of is because there is an RPM change. However it is two different things. A downshift is an actual gear ratio change. TCC or lock up is a way to control torque converter slip. The transmission should shift 1-2, 2-3, TCC & 3-4 or it may 1-2, 2-3, 3-4 & TCC depending on how it is programmed. So I suppose a more accurate description of my issue would be not that it up and downshifts, but that it does not stay completely locked into 4th gear and constantly fluctuates. Actually the better description would be that it is TCC hunting because you have proven that it is not a 4-3 downshift. If you have not tried this. When is makes the "downstift" as you call it. Pull it down to 3rd manually. If you still feel it then make a 4-3 downshift. You have again proven the TCC hunting (what Frank was talking about in an earlier post) aspect. Also I have experienced the random shaking/vibrations that can accompany trans issues like this. It felt like I was driving over the rumble strip thats built into the side of highways to notify drivers when they're drifting into the shoulder or oncoming traffic. These 2 statements are what we call "TCC shudder" in the trade. A little tube of "shudder fix" from a parts store or a bottle of GM limited slip additive from the dealer may help. I think you are describing a glazed converter that will need to be replaced. The problem here is in the valve-body. The TCC regulator valve & TCC isolator valve wear the bore of the valve-body and it starts to loose apply pressure. There are a couple of things you could try but they may be short term fixes. A Fitzall replacement valve, a TransGo SK TCC regulator valve and spring & the third option is to replace the spring in between the 2 valves with a 1" long piece of 3/16" brake tubing. All of these require a V-B R&R. If any more details are needed, please let me know.
I had good results back in the day fixing TCC shudder with the TransGo SK4L60E kit and just replacing the the TCC valve. I used the PR springs and that valve. 80% plus fix rate. We used to sell the fix for $600 if it didn't work the trans job would be $2150.00. I helped a friend fix a 1998 Bravada 4.3L with the TCC shudder about a year ago with that kit. If you shop wisely they are on eBay for under $40. Then you would want VB gaskets, fluid and filter too.
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From: BERWICK PA
Ah TCC shudder. Not mentioned in original post. That would point to worn or glazed converter clutch as mentioned,
You can try the FITZALL valve fix but likely damage has been done already. Likely the issue is why the flush may have been done, As for not throwing a code while not for sure someone could have just gone in a tuned out the 1870 code just for the point of sell the vehicle, I have seen that before. Look and find the box unchecked that will keep the light off and report no codes.
if it was me I would plan at min a new converter and VB fix or replacement, But honestly if it's over 100k miles i would do a trans rebuild and converter if i was gonna keep it.
The shudder is the key to this diagnosis, Shudder fix may fix the shudder but doubtful to fix the lock unlock issue IMO.
You can try the FITZALL valve fix but likely damage has been done already. Likely the issue is why the flush may have been done, As for not throwing a code while not for sure someone could have just gone in a tuned out the 1870 code just for the point of sell the vehicle, I have seen that before. Look and find the box unchecked that will keep the light off and report no codes.
if it was me I would plan at min a new converter and VB fix or replacement, But honestly if it's over 100k miles i would do a trans rebuild and converter if i was gonna keep it.
The shudder is the key to this diagnosis, Shudder fix may fix the shudder but doubtful to fix the lock unlock issue IMO.
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From: MN
Ah TCC shudder. Not mentioned in original post. That would point to worn or glazed converter clutch as mentioned,
You can try the FITZALL valve fix but likely damage has been done already. Likely the issue is why the flush may have been done, As for not throwing a code while not for sure someone could have just gone in a tuned out the 1870 code just for the point of sell the vehicle, I have seen that before. Look and find the box unchecked that will keep the light off and report no codes.
if it was me I would plan at min a new converter and VB fix or replacement, But honestly if it's over 100k miles i would do a trans rebuild and converter if i was gonna keep it.
The shudder is the key to this diagnosis, Shudder fix may fix the shudder but doubtful to fix the lock unlock issue IMO.
You can try the FITZALL valve fix but likely damage has been done already. Likely the issue is why the flush may have been done, As for not throwing a code while not for sure someone could have just gone in a tuned out the 1870 code just for the point of sell the vehicle, I have seen that before. Look and find the box unchecked that will keep the light off and report no codes.
if it was me I would plan at min a new converter and VB fix or replacement, But honestly if it's over 100k miles i would do a trans rebuild and converter if i was gonna keep it.
The shudder is the key to this diagnosis, Shudder fix may fix the shudder but doubtful to fix the lock unlock issue IMO.
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From: MN
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Good used is just that, used. The root issue is how long will it go?
Rebuilt is a used transmission that has been thoroughly inspected and rebuilt. The real issue there is how good is the re-builder and to what extent does he go to? Does he vacuum test pumps & valve bodies and then address the findings. Ream the PR bore if required, Some do it as part of the rebuild process. Others do not! Does he press the input drum apart and reseal the shaft/drum assembly. Does he replace all the seals or just the needed ones. Do they replace the bushings or just the front pump bushing itself.
So there are different skill levels of re-builders and there is the root issue still. How long will this go?
Hopefully there is a 100K difference.
I bought my 2004 Trailblazer from a couple that had just put in a 125K motor on a 300K vehicle. Transmission went out 2 weeks later. Wife said I'm not going without a vehicle for another 6 weeks. she went and bought a GU Traverse. Sold me the Trailblazer for $600 and I rebuild the transmission and now have 50K on it now. It was well worth the $900 in parts I put in for the rebuild. Transmission parts, converter, radiator, cooler lines & shifter cable.
Rebuilt is a used transmission that has been thoroughly inspected and rebuilt. The real issue there is how good is the re-builder and to what extent does he go to? Does he vacuum test pumps & valve bodies and then address the findings. Ream the PR bore if required, Some do it as part of the rebuild process. Others do not! Does he press the input drum apart and reseal the shaft/drum assembly. Does he replace all the seals or just the needed ones. Do they replace the bushings or just the front pump bushing itself.
So there are different skill levels of re-builders and there is the root issue still. How long will this go?
Hopefully there is a 100K difference.
I bought my 2004 Trailblazer from a couple that had just put in a 125K motor on a 300K vehicle. Transmission went out 2 weeks later. Wife said I'm not going without a vehicle for another 6 weeks. she went and bought a GU Traverse. Sold me the Trailblazer for $600 and I rebuild the transmission and now have 50K on it now. It was well worth the $900 in parts I put in for the rebuild. Transmission parts, converter, radiator, cooler lines & shifter cable.
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From: Wichita KS / Rancho San Diego
If it were I, I'd try the Fitzall or the Transgo kit with their TCC valve. Neither would be hugely expensive, and just may give you enough increased apply pressure that lock-up will hold.
If it fails, then you'll know you'll need to get into more extensive work.
If it fails, then you'll know you'll need to get into more extensive work.
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From: MN
Good used is just that, used. The root issue is how long will it go?
Rebuilt is a used transmission that has been thoroughly inspected and rebuilt. The real issue there is how good is the re-builder and to what extent does he go to? Does he vacuum test pumps & valve bodies and then address the findings. Ream the PR bore if required, Some do it as part of the rebuild process. Others do not! Does he press the input drum apart and reseal the shaft/drum assembly. Does he replace all the seals or just the needed ones. Do they replace the bushings or just the front pump bushing itself.
So there are different skill levels of re-builders and there is the root issue still. How long will this go?
Hopefully there is a 100K difference.
I bought my 2004 Trailblazer from a couple that had just put in a 125K motor on a 300K vehicle. Transmission went out 2 weeks later. Wife said I'm not going without a vehicle for another 6 weeks. she went and bought a GU Traverse. Sold me the Trailblazer for $600 and I rebuild the transmission and now have 50K on it now. It was well worth the $900 in parts I put in for the rebuild. Transmission parts, converter, radiator, cooler lines & shifter cable.
Rebuilt is a used transmission that has been thoroughly inspected and rebuilt. The real issue there is how good is the re-builder and to what extent does he go to? Does he vacuum test pumps & valve bodies and then address the findings. Ream the PR bore if required, Some do it as part of the rebuild process. Others do not! Does he press the input drum apart and reseal the shaft/drum assembly. Does he replace all the seals or just the needed ones. Do they replace the bushings or just the front pump bushing itself.
So there are different skill levels of re-builders and there is the root issue still. How long will this go?
Hopefully there is a 100K difference.
I bought my 2004 Trailblazer from a couple that had just put in a 125K motor on a 300K vehicle. Transmission went out 2 weeks later. Wife said I'm not going without a vehicle for another 6 weeks. she went and bought a GU Traverse. Sold me the Trailblazer for $600 and I rebuild the transmission and now have 50K on it now. It was well worth the $900 in parts I put in for the rebuild. Transmission parts, converter, radiator, cooler lines & shifter cable.