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4L80E 2nd and Rev Only

D

dalejohnson2000

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Messages
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Hey
I’m new to the site. It looks like there are some experienced folks reading some of the threads.
I have a 1994 P30 454ci 4L80E under a motor home. We are at a camp site now so there is not a lot I can do here.
Driving here, all was well. Stopped at stop light. Pulling away it my have shifted 1 to 2. But I noticed when it wouldn’t shift to 3rd. Tried to shift with column shifter. No help. Puked over and checked the fluid, good. No leaks. Temp around 150 normal.
So all I have is 2nd and reverse. I drove to the campground 20 miles at 35 mph. Temp never above 180. OBD I system, no check engine light.
Shift solenoids first thought. But both at the same time.
Saw a post that the 4L80E with no electronics will have 2nd and Reverse.
Saw a youtube post to shift a 4L80E with switches manually.

So 200 miles from home. Not many tools.
I can try the switches
I can buy a PCM
I could change shift solenoids at the campsite but not fond of that idea.

I have a multi meter. But not sure what and how to check sitting still.

Thanks in advance
 
I figured that is the limp mode.
I just checked for codes, none there. So when we make camp we hit the battery disconnect. So if there were any codes they were erased. When we hit the road tomorrow I can check.
Thinking of a limp mode home. I was mistaken earlier. It is 2 hr. Not 200 miles. So maybe 4 hr in limp mode. Worse gas mileage. Watch temps. And cruise slow…

At home I can better TS it and wait for parts as needed.
 
Unplug the main wiring harness that goes into the transmission (by the shift selector on the driver's side of the transmission. See if either side of it, the plug or socket, has transmission fluid in it. If so, there's your culprit for the no signal limp mode. If you have access to some electrical contact spray, blast out and let dry both halves and reconnect. Odds are you'll now have full transmission function.

Transmission fluid seeping past the internal harness seal and into the external connector on the transmission side and then causing electrical connectivity issues is a common problem with the '94-'96 series 4L80E's.

I'd be hesitant to use brake cleaner to clean out the plug and socket for fear that it would soften the plastic.
 
Update. Contact cleaner last night. Dried overnight.
Plugged it in. 1st gear only.
Stopped
Unplugged
2&R
Drove it home. Hope none of y’all were behind me.
At home, plugged it back in.
Test dove it.
2&R
Back home, frustrated, disconnected batteries. And then I realized I cleared the codes again (if any).
So the A solenoid works, maybe sometimes.
But it doesn’t shift.
Beat today. I’ll take it for a spin tomorrow and check for codes.
So I will be getting a new internal wiring harness and exterior pigtail. Debating the solenoids. Even if they work. 30 yrs and 94k miles. I’m thinking replace them too. Any particular brand folks like or ones to stay away from?
I don’t think these are root causes, but needed. Although cleaning changed things. We’ll see.
May have some code info tomorrow.
 
Genuine ACDELCO electronic parts only. The ONLY exception would be name brand transmission replacement/upgrade parts by Sonnax or other professional transmission rebuild suppliers.
 
Electrical gremlins can be a real PITA to hunt down and find. Other possible electrical causes can be a female (or two) bullet connector in the female harness connector may have spread open slightly and cause no/intermittent connectivity. Could also be a wire has fatigued and broken off of its female/male bullet inside the plug/socket connector. Could also be in the external transmission wire harness with a broken wire, frayed wires shorting to each other or a wire shorting to ground.

The fact that plugging/unplugging the harness changed what gears you had available does point strongly to a connection issue internally with either connector half, but don't put all your eggs into that basket.
 
The atf causes shorting- it is possible to smoke the control module as well. But always start with known bad parts imo.
This is an example of easy to start throwing a ton of parts at something without results.
Absolutely start with new harness. Then dive into the diagnostic procedures from GM to avoid tons of new parts and hours invested.

I wouldn’t just replace part’s because they are old. That reasoning says have transmission fully rebuilt and replace the entire harness with ecm/tcm.

P30- you could have almost any combination in this rig. Fill out your signature line with some specific details. Do you have a ds4 or db2 ip? Tcm or ecm? If not sure, post multiple pics so we can identify for you. If you smoked a tcm, they are getting ridiculous to find. Often cheaper and better to get a stand alone controller but you need to know the harness is perfect first and that the trans internals are functioning right or you won’t get the new Controller set up right.

New parts are not always good parts, mass production errors occur. Don’t just replace the solenoids with out testing. Everything in there needs tested before replacing because if you swap an old working part for a new defective- your troubleshooting will be a nightmare and you will then keep changing parts thinking it is something else. Eventually you change all the parts and it still doesn’t work right because the first or second part you put in is bad. Sounds far fetched- but seen it happen multiple times. I would estimate 1/75 parts comes wrong or defective.

So yes replace that proven bad internal harness. Fully clean the other connection. Then test drive. Next would be try again for codes since now hopefully everything is communicating properly then a pressure gauge while driving recording whats happening.

Seriously need the diag flow chart here.

@THEFERMANATOR any advice?
 
ReCap/Update
5-21 Driving fine. Stopped at red light. Stuck in 2nd.
Pulled over. Check fluids-ok. Only 2nd Rev
Limped to camp. Drive temperature
5-23 Found small amount of oil in connection
Contact cleaner.
5-25 Leave camp. 1st gear only. Cold Tranny.
Unplugged transmission from PCM.
Limp home in 2nd.
Arrived, plugged transmission back to PCM. 2nd Rev. Drive temp tranny.
5-26 Drove today. Plugged in from yesterday. Cold Tranny. 1st gear only.
Never has had a check eng light. Checked for codes after short drive stuck in 1st. No codes. Only code 12.

The Tranny shift solenoids have a dedicated 20amp circuit from fuse box. Fuse checks good. First gear requires Sol A to be on and needs 12v. So power and wire to tranny confirmed.
5-21 check Shift solenoids 25 ohms. TCC was…don’t remember but was in range of the post I saw.
No codes. Transmission codes added for 1994 and later. Chassis mfg 6-22-94. 95 model MotorHome. PCM is a reman unit. It may be possible that the unit is a pre 94 firmware.
Head scratch.
I have a new pigtail ordered. To make the manual shift set up. This Will check the solenoids. Hopefully this works.
Then cut out the old pigtail and use new external plug. Will test. Hopefully good.
Going to order internal harness. Debating solenoids. I think they are good. We’ll see. But they are old…I’m in there. New filter and fluid less than 2000 miles.
 
Will L, I saw your last post after my last post. Just sent pics of PCM and Veh Vel Buffer module.
Thanks for the don’t change for the sake of new. That is my normal philosophy. And I have found bad new parts…after much frustration But dumping fluid is such a pita. When I changed the fluid I added a pan fluid temp gage and now have a drain hole. And filling the tranny is a bigger pita on this MH. Used transfer pump last time.
So
Plan
New external plug. Known exposed to oil.
Test solenoid shifting with switches
Assume good
Rewire/replace external plug as original to pcm. Test
Replace internal harness, order AC Delco today. Known leaking.
May have updates this weekend.

Thanks again for great support and advice!
 
Hey, sorry. I always have 6.2/6.5 diesel on my mind here, disregard db2/ds4 comment. I forgot you have a 454.

Again, it would help to list these details in your signature line when we read the current post, as we see not only your thread but sometimes a couple dozen a day. Then also go to other forums. So your post becomes one of 3 dozen possible each day. And no one is going to reread the full thread each time to remind if you have diesel/ gas/ carburetor/ efi/ etc. So please fill out signature line.

But lets play the similar version in gasoline 454. Carburetor or throttle body with full voltage tps and converter? Efi with 0.5-5v tps? Efi? Mpfi? There are a ton of things that could be there and each one has differing control options that all input to how and when the transmission shifts.
 
dalejohnson2000 said:
Will L, I saw your last post after my last post. Just sent pics of PCM and Veh Vel Buffer module.
Thanks for the don’t change for the sake of new. That is my normal philosophy. And I have found bad new parts…after much frustration But dumping fluid is such a pita. When I changed the fluid I added a pan fluid temp gage and now have a drain hole. And filling the tranny is a bigger pita on this MH. Used transfer pump last time.
So
Plan
New external plug. Known exposed to oil.
Test solenoid shifting with switches
Assume good
Rewire/replace external plug as original to pcm. Test
Replace internal harness, order AC Delco today. Known leaking.
May have updates this weekend.

Thanks again for great support and advice!
Click to expand...
Added info
With pcm unplugged from tranny gave no fault. My pcm must be pre-94 unit.
 
The best way to check a solenoid is with a amperage test. This will test both the wiring and solenoid at the same time if you do the test at the PCM connector. This is my preferred way of diagnosing these issues at work.

1. Amp draw test the solenoids at the Powertrain Control Module (PCM) by disconnecting the PCM connector and grounding the shift solenoid wire through an ammeter.

2. Compare the 1/2 shift solenoid to the 2/3 shift solenoid. They should both take about 0.5 amps.

3. If one solenoid is low check for a wire problem by grounding it at the transmission connector.

4. If both are OK and matching, use jumper wires to ground the solenoids and unground the solenoids to see if the transmission will shift through all the gears. If not problem is in the transmission.
 
@dalejohnson2000 you said you had the transmission pan off to do a fluid change and add a drain plug a while back, right? It is quite possible (and it happens more than you think) that you got part of the internal transmission wiring harness pinched between the pan and pan rail, or filter and valve body, during reassembly. Eventually the insulation degrades and you get a direct path to ground or an open circuit in the harness.
 
It is always possible that the wires got damaged. But I will know when they are replaced next week.
But...we can scratch off the guts. They are good.
I got the external pigtail today and so I set up the switches.
SW1 to Sol A
SW2 to fake something
SW3 to Sol B
SW4 to TCC
Put it in OD on the shifter, SW1 on is First, SW1 off is Second, SW3 on is Third, SW1 & SW3 on is Fourth, SW4 is TCC lock up.
1685235335050.png
Not sure what color switch plate cover to get. :) Almond is so 90's.
So it worked great, I have never been so happy to know something else is broke.
The internals are good.
As I was driving, I was wondering how B&M or TransGo can sell a Shift Kit on these.
This set up has full pressure the revs will give and hold the gear, and it thumps into the next gear on the switch.
So internal wiring is next. That will give new wires inside and out. External pigtail will be soldered and heat shrink.
I'm betting (hoping) that this does the trick.
But if not...
we have MAP, TPS, Speed Sensors, Vehicle Speed Buffer Module, PCM (other?).
MAP and TPS have some tests I've seen posted.
Not sure how to test the others.
 
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