Trans not getting into 4th and 5th - what gives?

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e9999

e9999

Gotta get out there...
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Odd thing happened today, first time ever. Noticed the rpm was higher than usual and realized that the transmission appeared to be stuck in 3rd or below. Could not get it to go into 4th (or 5th, IIRC but not 100% sure). This kinda puts a damper on expected drives.
I don't know much about A/Ts.
First things to look at / do IYO? The ATF was not changed recently, I could change that easily enough. Any chance that would do something? Could it be the linkage? Dirty filter? Or -shudder- some issue in the valve body?
Thoughts on how to diagnose this and getting started on fixing this properly?
 
First, I'd check engine coolant temp (ECT). Do this through tech stream, with any OBD connecting device. ECM must read above ~120F, for A/T to shift to higher gears. If coolant level low, it can be below ECT sensor, placing sensor in air. Or if thermostat opening (weak) to soon, ECT may be low.

Second, look at A/T wire housing. Look for any damage, such at rodents chew wires. Or perhaps someone working on starter, needlessly disconnect one or more of the wire harness blocks. Those, sitting on bellhousing where it bolt to the block. The wire housing on the LH (driver side), is a locking/sealing one. If not locked, water may have gotten in. Over time can result in change in resistance. Which confuses signals to solenoid.

I'm currently exploring A750f solenoids' wire housing block and capillary action. Which is drawing ATF out of A/T into wires/wire housing. Make sure to check for fluid in housing.
2001LC

Thread 'Alert, Alert, Alert----- Transmission valve body wire housing block! --- Have you looked into yours? Capillary action drawing ATF in!'

This automatics transmission's (A/T), wire housing block on driver side (LH) of A/T. Which connects to solenoids & temp sensor(s) within A/T case on valve body. Is heavily coated inside with a gray/green GOO. What is this GOO?

Any guesses what thick appearing oil substance is?

Anyone have pictures or can comment on theirs, they care to share here?

Edited 12/14/25:

As you read through this thread. It will become apparent we've ATF capillary actuation issues with: Transmission wire, that come out of A/T case from inside transmission. It's the wire housing, that connects all valve body...
 
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No 4-5th 03LX FSM.webp
 
thanks! good to know about that coolant temp circuit. Would not have thought of that. I don't recall that the temp reading on the dash was off but will check.
 
e9999 said:
thanks! good to know about that coolant temp circuit. Would not have thought of that. I don't recall that the temp reading on the dash was off but will check.
Click to expand...
Don't trust dash water temp gauge. You need to see what ECM sees ECT at, through tech stream.
98-02 have two ECT sensors. One is for the dash gauge, they other for ECM.
 
I don't have techstream. Would one of those OBD2 readers that can see sensor readings work for that? This is an '03 if it matters.
 
No OBD code that I can see. Oddly, there are 4 incomplete monitors, though. No idea why that would be, I have driven it a good bit since the last battery disconnect.
 
That could be a give away that something isn't communicating, maybe?
 
could be indeed.
Oddly, today it drove just fine, changed gears nicely. Not a problem. And no more incomplete monitors per the OBD. So, looks like something happened with the battery / comm system / computers that created an odd situation that did some sort of reset maybe?
Does this ring a bell, somebody?
I'll gladly take this over the gears being permanently out of commission, TBH, but that's still not great. May happen again, so I'll be keeping an eye on this for a bit.
Could it be some dirt that blocked a trans body valve and got released somehow? Worth changing the fluid over you think?
 
I'm leaning toward electronic, not mechanical. Low voltage or anything lately?
 
yes, could be, those monitors not ready is what I normally see after disconnecting the battery. I'll go test it.

added: battery appears to be on the weak side (12.4V after about 30mins driving today) but is not obviously bad. Hard to believe it would have been so low to disconnect everything and even if so, why would that do something to the trans? Battery has been disconnected many times before and never seen the trans limiting gears. ATF is plentiful and nicely red. Gotta get a better OBD reader too, what the latest consensus on best DIY one?
 
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Stumbled over this going through some old threads I follow. Might be worth your time. TL;DR: wheel speed sensors caused 4th and 5th gear issues.
 
interesting, will look into that, thanks
 
98% changes, this is electrical.
I'd be checking all wires and wire housing blocks.
  • ECT
  • Harness to & on A/T.
  • Behind glove box at CPUs
Also, take note of moisture, before, during and after no shift 4 to 5th. i.e.: wet roads, rain, snow, car wash, etc.
 
^I agree.

There is no risk in changing the ATF and if you haven't done it in the last 24 months, you should. BTW, there is no filter in the transmission.

FWIW, I'd invest in a dongle for Techstream before I spent a dime on an aftermarket OBDII reader. Same price (or less) and more utility.
 
2% chance, a flush will help.
If you've been doing drain and fills, rather than full 12 qt flush. Then I would do a 12qt flush.
It would be a good idea to pull sample from mid stream, while draining pan. Sent that sample to Black Stone.

I like Mobil 1 ATF best of all, for the 98-02 100 series.
 
Thanks and, yes, it seems that the weird issue of monitors not ready is either a freaky coincidence or a strong hint that something electrical happened.

No trans filter? Weird. I had assumed there is one. ('03 here)

So far, it's driving just fine again. Good point about the moisture, but there was no rain or car wash since well before the incident so that may be a long shot.

I'd love to have techstream but it seems like quite the ordeal to get going and it would also be expensive to subscribe (more than a standalone unit?) if I work on this for more than a couple of days, from what I remember.

I'll probably focus on electrical over ATF for now, then.
 
well, astonishingly, all has been well for over a week. Trans shifts smoothly as usual in and out of 4th and 5th. No problem. No codes or incomplete monitors to be seen.
Must have been a freaky electrical glitch. Would like to know what, though.
Any guesses?
 
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