Transmission issues

[Kohl]

Hello, I have a 95 Chevy suburban k1500 4x4. The transmission that was in it was shot so I put in a jasper rebuilt transmission and it worked beautifully. Then a couple of months pass and now I'm getting a check engine light and it gets stuck in 3rd gear. I found information about the 96+ having exactly the same problems I was having with a transmission flare causing the issues, problem though I don't have the computer that needs to be grounded from the 96+. So now I'm frustrated and don't know what to do or even look for... Does anyone have any ideas? Does anyone know if the nv3500 will just bolt to the 5.7, I know that it's a big process but I'm thoroughly done with automatics.

 

[Scooterwrench]

All computers have to have a ground. The NV3500 was used in trucks behind 350's.

 

[JPVortex]

Swap it you won’t regret it I swapped mine a few months ago from 4L60E to 5LM60(earlier version of NV3500) had never done a manual swap or anything before this one) on my 94 k1500! It wasn’t that bad, just have patience and do your research.

 

[NickTransmissions]

Hello, I have a 95 Chevy suburban k1500 4x4. The transmission that was in it was shot so I put in a jasper rebuilt transmission and it worked beautifully. Then a couple of months pass and now I'm getting a check engine light and it gets stuck in 3rd gear. I found information about the 96+ having exactly the same problems I was having with a transmission flare causing the issues, problem though I don't have the computer that needs to be grounded from the 96+. So now I'm frustrated and don't know what to do or even look for... Does anyone have any ideas? Does anyone know if the nv3500 will just bolt to the 5.7, I know that it's a big process but I'm thoroughly done with automatics.

Try and relax, take a couple deep breaths...What codes are being set and stored?

Id find that out first before doing anything else.

The transmission is in limp mode so there's almost certainly at least one transmission DTC stored in the computer. Limp mode is caused when the PCM is no longer seeing/receiving voltage input signal from one or more electronic components in the transmission. Sometimes it's the component itself (shift solenoids, pressure switch, etc) other times there are one or more shorts the transmission internal harness or external harness or even PCM itself.

Scan the PCM, see what the code is (will be a two-digit code since you have a 1995) and let us know what you find.

 

[Scooterwrench]

Manual transmissions lack this AFAIK and so you'll have to likely swap your PCM (or reprogram it) to work with the manual transmission so it's not looking for the park/neutral signal from the MLPS.

Yeah,Nick. Manuals use the clutch switch to disable the starter until you mash the clutch pedal to the floor.

 

[AK49BWL]

MLPS: Also, since you have a 1995, you likely have a manual lever position sensor on the outside of your transmission. The MLPS works with the pressure switch manifold to communicate range position to the PCM...The MLPS communicates the position the instant you go 'key-on' then hands things off to the pressure switch manifold assembly when the engine fires up...before that engine is allowed to start, the PCM must receive the park/neutral signal on channel N from the MLPS during the key on, engine off portion of the cycle...If not, you won't be able to start your car...Manual transmissions lack this AFAIK and so you'll have to likely swap your PCM (or reprogram it) to work with the manual transmission so it's not looking for the park/neutral signal from the MLPS.

95+ automatic GMT400s do have this external range-select switch on the side of the transmission, however none of it is connected to the PCM at all, and the PCM has no control over whether the truck's starter can be engaged or not. The side-mounted switch body is there for the gear-shift indication in the cluster and Park/Neutral safety (for starter motor engagement) only.

 

[NickTransmissions]

95+ automatic GMT400s do have this external range-select switch on the side of the transmission, however none of it is connected to the PCM at all, and the PCM has no control over whether the truck's starter can be engaged or not. The side-mounted switch body is there for the gear-shift indication in the cluster and Park/Neutral safety (for starter motor engagement) only.

Ah, you're correct..It's actually the pressure switch manifold assembly that informs range position to the PCM not the MLPS, I did mix them up. Thanks for the correction.

 

[Kohl]

Swap it you won’t regret it I swapped mine a few months ago from 4L60E to 5LM60(earlier version of NV3500) had never done a manual swap or anything before this one) on my 94 k1500! It wasn’t that bad, just have patience and do your research.

So the nv3500 will... " Plug and play" right to the engine with no problem? I understand that I will have to cut a hole in the floor, pedal assembly, gear swapping, electrical deleting and possibly changing PCM. Otherwise just plug and play?

 

[Kohl]

Try and relax, take a couple deep breaths...What codes are being set and stored?

Id find that out first before doing anything else.

The transmission is in limp mode so there's almost certainly at least one transmission DTC stored in the computer. Limp mode is caused when the PCM is no longer seeing/receiving voltage input signal from one or more electronic components in the transmission. Sometimes it's the component itself (shift solenoids, pressure switch, etc) other times there are one or more shorts the transmission internal harness or external harness or even PCM itself.

Scan the PCM, see what the code is (will be a two-digit code since you have a 1995) and let us know what you find.

I don't have the computer to be able to read any codes so I went down the list. New PCM, throttle position sencer, all new and cleaned fuses/fuse inserts, all new sensors, fluid is correct and to the correct level and lastly shift position is correct. I took it to a transmission shops to see if they can figure out if it's electrical but they said that it was
the wrong transmission and trying to upsell for a
new/rebuilt transmission. It's not I made sure before I made a purchase that it was the correct transmission, also if it was a 94- I'd have a lot more problems pretty early on, not months after.

 

[NickTransmissions]

I don't have the computer to be able to read any codes so I went down the list. New PCM, throttle position sencer, all new and cleaned fuses/fuse inserts, all new sensors, fluid is correct and to the correct level and lastly shift position is correct. I took it to a transmission shops to see if they can figure out if it's electrical but they said that it was
the wrong transmission and trying to upsell for a
new/rebuilt transmission. It's not I made sure before I made a purchase that it was the correct transmission, also if it was a 94- I'd have a lot more problems pretty early on, not months after.

Hmmm, agree if that is what they told you...If you had a 93 or 94 unit that wasnt converted to work with your 95 PWM TCC apply (ie 95 pump, vb and spacer plate installed) then you'd have problems that would have materialized sooner than now.

95 is a stand alone year due to first year pwm tcc apply strat and last year of pwm 3-2 downshift design so they can be harder to find. So if you have a 1996 or 97 installed the 3-2 ctrl solenoid would stick out to your pcm and it would likely throw a code, hence why it's important to scan the pcm.

You can also use a paper clip to ascertain the codes. Search "read OBD1 codes with paper clip" or similar..