1996 4L80e: Have 2nd and reverse only no codes

[RedVenom48]

Success!!! We have shifting! All 4 forward speeds and reverse!!! Looks like the little voice in my head that told me to replace the solenoids and pressure switches with the pan off was right.

In total I replaced the following:

1 Input shaft speed sensor (genuine GM)
1 Internal trans harness (NAPA, made by Rostra)
2 Shift Solenoids: 1-2 and 2-3 (Genuine GM)
1 Pressure switch pad (Genuine GM)
1 Torque Converter Solenoid (Carquest)
1 Trans pan gasket (Amazon China special ...will probably leak later haha)
5 quarts of ATF (Valvoline max life Dexron compatible)

Again, this was to fix a reverse and 2nd gear only condition, NO DTCs. Shift 1-2 was failed open, Shift 2-3 was below spec on resistance. TCC solenoid ohm'ed ok as well as the Pressure control solenoid. I dont have a way to adjust pressure so I rolled with the installed Pressure control solenoid.

Amazingly enough, the transmission shifts very smoothly. Much better than I anticipated it would given what its been through and having 195k on the clock. To be clear this is with just me in the Burban, ambient temps in the 70s driving on the street. Will take her on the freeway later to see how it does. Ive also got my 73 Nova hanging out at a buddies house that I need to get, so that should be a decent test for towing.

Frankly, I've got no expectations going forward. My hope is that the robustness the 4L80 is famous for translates to my specific Suburban. The Carfax did show frequent servicing, so my hope is the internals have some decent life left in them before a true rebuild will be needed. I bought this thing for $1000 bucks, and while she's.... rough inside, if she is mechanically solid thats all I can really ask for.

 

[NickTransmissions]

Success!!! We have shifting! All 4 forward speeds and reverse!!! Looks like the little voice in my head that told me to replace the solenoids and pressure switches with the pan off was right.

In total I replaced the following:

1 Input shaft speed sensor (genuine GM)
1 Internal trans harness (NAPA, made by Rostra)
2 Shift Solenoids: 1-2 and 2-3 (Genuine GM)
1 Pressure switch pad (Genuine GM)
1 Torque Converter Solenoid (Carquest)
1 Trans pan gasket (Amazon China special ...will probably leak later haha)
5 quarts of ATF (Valvoline max life Dexron compatible)

Again, this was to fix a reverse and 2nd gear only condition, NO DTCs. Shift 1-2 was failed open, Shift 2-3 was below spec on resistance. TCC solenoid ohm'ed ok as well as the Pressure control solenoid. I dont have a way to adjust pressure so I rolled with the installed Pressure control solenoid.

Amazingly enough, the transmission shifts very smoothly. Much better than I anticipated it would given what its been through and having 195k on the clock. To be clear this is with just me in the Burban, ambient temps in the 70s driving on the street. Will take her on the freeway later to see how it does. Ive also got my 73 Nova hanging out at a buddies house that I need to get, so that should be a decent test for towing.

Frankly, I've got no expectations going forward. My hope is that the robustness the 4L80 is famous for translates to my specific Suburban. The Carfax did show frequent servicing, so my hope is the internals have some decent life left in them before a true rebuild will be needed. I bought this thing for $1000 bucks, and while she's.... rough inside, if she is mechanically solid thats all I can really ask for.

Glad you got it fixed, figured it was harness and/or solenoids - they are almost always either already bad or about to go bad when a 4L80 comes in for overhaul...Now you know to always replace electrical and electronic components (all of them) and only use either Genuine GM, Borg Warner or Rostra (those are really the only three brands I've had consistent success with).

 

[RedVenom48]

@NickTransmissions I certainly did appreciate your pointers, they certainly helped!

As for the transmission, I drove it in to work today and well.... unfortunately.... we have a failure. For an all too brief weekend, the solenoids had fixed this stubborn 4L80. Great and smooth shifts, couldn't have been happier. Unfortunately, it was not to last.

On the drive home from work, dealing with some light traffic I lost overdrive. After coming to a stop at my exit, I had VERY hard 1-2 upshifts and and harder than normal 2-3 upshift. Still no overdrive. Getting home and going into reverse, I had a very hard reverse engagement as well as a harsh reverse to drive engagement. Some very brief Googling shows that I could have one of 2 failures, both of which will require a full rebuild. either the Actuator feed limit bore has been damaged and needs to be honed, or the 1-2 band servo circuit has failed internally. Again, very brief google searching.

Unfortunately Im tapping out. Will be going for sale this weekend. I do appreciate all the help and direction finding this board has given me regarding this. Thanks!

 

[NickTransmissions]

@NickTransmissions I certainly did appreciate your pointers, they certainly helped!

As for the transmission, I drove it in to work today and well.... unfortunately.... we have a failure. For an all too brief weekend, the solenoids had fixed this stubborn 4L80. Great and smooth shifts, couldn't have been happier. Unfortunately, it was not to last.

On the drive home from work, dealing with some light traffic I lost overdrive. After coming to a stop at my exit, I had VERY hard 1-2 upshifts and and harder than normal 2-3 upshift. Still no overdrive. Getting home and going into reverse, I had a very hard reverse engagement as well as a harsh reverse to drive engagement. Some very brief Googling shows that I could have one of 2 failures, both of which will require a full rebuild. either the Actuator feed limit bore has been damaged and needs to be honed, or the 1-2 band servo circuit has failed internally. Again, very brief google searching.

Unfortunately Im tapping out. Will be going for sale this weekend. I do appreciate all the help and direction finding this board has given me regarding this. Thanks!

Sucks, sorry to hear but the AFL bore is in the valve body and doesn't require transmission removal while the intermediate band in these transmissions is used only in manual 2nd (the 4L80E has an intermediate clutch pack used for 2nd gear while in D4 or D3. So something else is going on; whatever it is, it seems to be maxing the line pressure (could be a bad EPC or pressure switch manifold assembly or even a bad ECM...But yea, I hear ya - problems like this can be very frustrating and sometimes you need to cut your losses if the juice no longer seems to be worth the squeeze.

 

[RedVenom48]

Zombie thread time!

Well, since my last post I figured out what the hell was happening to my Burban. So, I lost overdrive and had HARD shifting 1-2 and 2-3. My best guess was something internal to the 4L80e. But after not driving it for a week I had to use it to take my waste oil to disposal.

I got in and to my complete surprise, the damn thing shifted like BUTTER. Smooth shifts and I had overdrive... Wtf?

Long story short I was able to get it to fail and then recover a few more times. I plugged my scanner in when running ok and then scanned for data when it started malfunctioning. When malfunctioning, I saw that my MAF data was indicating a failed MAF. Reving the engine it was only outputting .04 g/s etc. When normal, Id see a wide spread in the teens and 20s! Again, no Check engine light and no pending or current codes when the MAF failed.

My guess is that the 1996 isn't an enhanced OBD2, so it didn't know the MAF data was wildly out of range. It was making changes to everything including shifting. The A/F was checked via the MAP and O2s so it never ran absurdly poorly.

I replaced the MAF sensor and drove it a few days a row and absolutely butter shifting and the engine ran better.

The rest of the Burban is not in great shape though, so I've decided to use it as a donor and swap the 7.4 Vortech and 4L80 into my Nova project. I plan on pulling everything since I have a solid running donor and I'll do the 0411 PCM swap.

Hopefully, this will help some fellow 7.4 Vortech owners out there!!

 

[Supercharged111]

In the event of a MAF failure these trucks default to max line pressure. Good thing you didn't put it up for sale.

 

[Road Trip]

Zombie thread time!

Well, since my last post I figured out what the hell was happening to my Burban. So, I lost overdrive and had HARD shifting 1-2 and 2-3. My best guess was something internal to the 4L80e. But after not driving it for a week I had to use it to take my waste oil to disposal.

I got in and to my complete surprise, the damn thing shifted like BUTTER. Smooth shifts and I had overdrive... Wtf?

Long story short I was able to get it to fail and then recover a few more times. I plugged my scanner in when running ok and then scanned for data when it started malfunctioning. When malfunctioning, I saw that my MAF data was indicating a failed MAF. Reving the engine it was only outputting .04 g/s etc. When normal, Id see a wide spread in the teens and 20s! Again, no Check engine light and no pending or current codes when the MAF failed.

My guess is that the 1996 isn't an enhanced OBD2, so it didn't know the MAF data was wildly out of range. It was making changes to everything including shifting. The A/F was checked via the MAP and O2s so it never ran absurdly poorly.

I replaced the MAF sensor and drove it a few days a row and absolutely butter shifting and the engine ran better.

The rest of the Burban is not in great shape though, so I've decided to use it as a donor and swap the 7.4 Vortech and 4L80 into my Nova project. I plan on pulling everything since I have a solid running donor and I'll do the 0411 PCM swap.

Hopefully, this will help some fellow 7.4 Vortech owners out there!!

RedVenom48,

Good troubleshooting, and kudos on not giving up. I especially liked your
technique of gathering 'known good' data when the truck was running right
so that you could compare & contrast this data with when it was running wrong.

And I found the failing MAF not kicking a code to be very interesting. Codes are good
when they show up and also provide actionable info, but they can definitely give the
owner a false sense of security/"it can't be that" when they don't kick. (!)

Your adventure is a perfect example of why when it comes to driving old, 'live data' is your
friend.

Thanks for sharing the solution and also coming back & closing the loop.

Enjoy that big block Nova. It should be a hoot!

Safe travels --

 

[RedVenom48]

RedVenom48,

Good troubleshooting, and kudos on not giving up. I especially liked your
technique of gathering 'known good' data when the truck was running right
so that you could compare & contrast this data with when it was running wrong.

And I found the failing MAF not kicking a code to be very interesting. Codes are good
when they show up and also provide actionable info, but they can definitely give the
owner a false sense of security/"it can't be that" when they don't kick. (!)

Your adventure is a perfect example of why when it comes to driving old, 'live data' is your
friend.

Thanks for sharing the solution and also coming back & closing the loop.

Enjoy that big block Nova. It should be a hoot!

Safe travels --

Road Trip, I appreciate the reply. It was quite vexing, especially being a former professional technician. Luckily I kept my wits and remembered my diag training once I realized the symptoms and conditions were not permanent. The 2nd gear only was fairly straight forward, but the random loss of OD and harsh shifting with no DTCs was unexpected. I think my data outputs on my scanner had 25 points of info. but there are only 5-6 main inputs that go into basic drivability. Given the 1st year nature of the 1996 OBD2, I eventually figured no codes would be set as the system just wasnt advanced enough. My guess is GM did the bare minimum to comply with the OBD2 mandate: set detection parameters and standardized generic codes for basic failures (P0XXX), CANBUS for code readers and scan tools to talk to the PCM and placing the OBD2 data port in a "conspicuous location to a crouching technician". Its entirely possible these fail conditions are listed in the factory GM manual, but I didnt see anything in my Chiltons. Perhaps it IS in the Chiltons, just buried.

​

Supercharged111, that makes a lot of sense now. PCM sees the MAP changes and 02 monitoring but doesnt know how much air is really getting it with weird MAF data range. Doesnt know how to correctly modulate pressures for a smooth shift, so it slams that **** home every upshift to make sure it at least doesnt wear out the clutches. I guess Im happy for that? Good lord though, that shift is HARD. God bless the 4L80e.

 

[Road Trip]

Its entirely possible these fail conditions are listed in the factory GM manual, but I didnt see anything in my Chiltons. Perhaps it IS in the Chiltons, just buried.

Sir,

Being somewhat new to the forum, I don't know if you are already aware of the GM
GMT400 Service Manuals that can be downloaded for free OVER HERE. In the first reply
are the majority of the manuals.

However, the manuals for your '96 didn't show up until later. No problem, here's
the link to the reply where you can see where to go for that download:

'96 C/K Manuals

I think that you will find these manuals to be a serious improvement over the Chilton's.

EDIT: In order to give you a taste of just how much better, I've attached a couple of
pages from the '96 FSM about the rules surrounding whether or not to report a
MAF Performance DTC P0101. (ie: Possibly you have another DTC that doesn't set
the SES light but at the same time wasn't allowing the testing/reporting of the MAF?
Or possibly the brand new '96 implementation of the OBDII coding was alright in
real-world driving, but the diagnostic section still wasn't quite ready for prime time?

Just a thought based on reading up on the MAF error reporting criteria. Anyway, get
those books asap, for there's plenty more to enjoy at your leisure.

Cheers --