2004 AWD Suburban 1500, When in Lo range, and shifted down to lock into 1st gear, truck won’t engage the 1st gear… only 2nd gear. When descending a steep off-road mountain side I need to crawl and my truck has the same crawl speed whether locked in 1st or 2nd gear 4Lo. This first began when attempting a crawl and truck lurched in and out of the 1st gear but eventually would never re-enter 1st. Problem has persisted ever since. Otherwise, transmission works smooth as butter in all other drive modes and conditions.
[SOLVED] 4Lo 1st gear
- Thread starter BPSmith
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Marky Dissod
Full Access Member
4L60E 1st gear (times) axle ratio (times) 4Lo gear reduction
3.06 * 3.73 * 2.72 = 31.05
3.06 * 4.10 * 2.72 = 34.13
Yeah, I see why GM avoided 1st gear in Lo ...
3.06 * 3.73 * 2.72 = 31.05
3.06 * 4.10 * 2.72 = 34.13
Yeah, I see why GM avoided 1st gear in Lo ...
Are you saying my gears are performing as designed, that there really isn’t an ability to lock-in 1st gear while in 4Lo?
AWD, or 2-speed 4wd transfer case? Pic of dash switch for 4wd modes?
Marky Dissod
Full Access Member
THINK I'm saying that, without an aftermarket pcm tune, GM's OE 'tune' might be preventing you from 1st gear in 4Lo?
Just as another example,
10L80 1st gear (times) the only axle ratio I've seen w/ 10L80
4.69 * 3.27 (no gear reduction) = 15.34
Since I've never tried/needed 4Lo I can't speak from experience, but '31' or '34' is a lot of torque multiplication for any gear.
You'd be forced to shift into 2nd @ or before 17MpH.
swathdiver
Full Access Member
Look up "Traction Assist System" in your owner's manual.
Mudsport96
Full Access Member
Yeah it is probably in the tune. I know that a good portion of the SUVs (and some but not all of the trucks) have a program that doesn't allow 100% throttle in low range if equipt with the electric throttle.
So it would not surprise me that off throttle deceleration in low would have something weird too. If I remember I will see what I can find in a tune tomorrow.
So it would not surprise me that off throttle deceleration in low would have something weird too. If I remember I will see what I can find in a tune tomorrow.
Mudsport96
Full Access Member
What speeds where you trying to do this at? The 04 suburban tune i am currently looking at, does not have "manual mode allowed" enabled. Which means you can put it in 1st, but it will still shift when it thinks it is supposed to. You could get the transgo manual 1st valve and put that in. Then you can override the ecm and it is simple to do. Or get a tune and have manual mode turned on.
It looks like 18mph is the limit that will hold 1st in low range in this particular tune. I dont imagine you were going that fast though.
It looks like 18mph is the limit that will hold 1st in low range in this particular tune. I dont imagine you were going that fast though.
It’s a BorgWarner 4485 transfer case. These are my switches
I will have my shop check this out. Thank you for the additional insight and your expertise!
Thank you for the additional insight, I’ll have the shop check this out as well.
Mudsport96
Full Access Member
I forgot about this case. It was in a youtubers Yukon xl that he put a turbo on. Yeah it died because he didnt know it was awd and he did a few pulls on a 2wd dyno.
I do not have a file to check to see if it is different from a regular 4x4 case vehicle, but I would think they are the same for shift timing
You are correct, I only need to crawl down a mountain side, typically under 10mph. I thought I had experienced this capability in the past but I definitely cannot crawl anymore. Would you still recommend these add-ons you listed above to achieve the ability to crawl in 4Lo, while shifted into 1st? Remember, this is an 2004 AWD suburb With Lo Range. Not a typical 2Hi/4Hi/4Lo model.
Marky Dissod
Full Access Member
Think you need your 'Manual Mode' 1Up2 & 2Dn1 shift tables reprogrammed/tuned so that, if you're already in 1st or going slow enough to safely downshift to 1st with the shifter, then once the shifter is in 1st it won't upshift except to protect the engine or transmission.
In 1stLOW, think that'd be about 18MpH?
In 1stLOW, think that'd be about 18MpH?
Marky Dissod
Full Access Member
Unfortunately, thought of another possibility ...
If so, that'd need a repair/replacement; transmission would need to come out.
Other possibility is that you've worn out/used up your 1st gear's overrun clutches.
If so, that'd need a repair/replacement; transmission would need to come out.
Wonder how it would act in "tow mode".
Mudsport96
Full Access Member
I would always use a transgo hd2 kit if I wanted to upgrade a 60e. Depending on miles, the spacer plate may be worn and be needing replaced too. Hard to tell from the outside though. The 60e in my Silverado had 200k on it, and the 2-3 checkball had almost made its way through the plate. Luckily the band burned up first.
Here is an update to the issue: The local Aamco shop kept my suburban for about two months, made several best guess repairs, charged me over $7k and the problem still exists. Full disclosure, I did not see many of your suggestions and expert insights in time to pass them along to the shop. And, I didn’t want to be “that guy” who tries to tell the experts how to do their job.
They did not remove and inspect the transmission since they rebuilt it two years ago and their diagnostics didn’t point to anything within.
Their latest diagnosis is that there is a problem with the engine wiring harness and communication between the shifter on the steering column is not sending the correct info to the transmission (this is my best description of their thinking, not theirs).
I have also discovered that the issue persists whether in Hi or Lo range, on flat ground or descending a hill. I.e. When the vehicle is at a stand still and I put the shifter in 1st or 2nd position and then begin to accelerate the vehicle has little power, it feels as though it’s trying to start from 3rd gear. But if I put the shifter in the 3rd or Drive position the vehicle has full power upon acceleration and all gear shifting works flawlessly. There seems to be a communication glitch when the shifter is in the 1st or 2nd position.
Aamco is suggesting replacing the wiring harness but having is having a difficult time hunting down the correct harness match for my 2004 AWD Suburban. They say the harness has the same part number for different drivetrain Chev vehicles, they have already ordered-in two and they do not match my vehicle’s needs. The search continues.
Does any of this sound familiar to you experts?
They did not remove and inspect the transmission since they rebuilt it two years ago and their diagnostics didn’t point to anything within.
Their latest diagnosis is that there is a problem with the engine wiring harness and communication between the shifter on the steering column is not sending the correct info to the transmission (this is my best description of their thinking, not theirs).
I have also discovered that the issue persists whether in Hi or Lo range, on flat ground or descending a hill. I.e. When the vehicle is at a stand still and I put the shifter in 1st or 2nd position and then begin to accelerate the vehicle has little power, it feels as though it’s trying to start from 3rd gear. But if I put the shifter in the 3rd or Drive position the vehicle has full power upon acceleration and all gear shifting works flawlessly. There seems to be a communication glitch when the shifter is in the 1st or 2nd position.
Aamco is suggesting replacing the wiring harness but having is having a difficult time hunting down the correct harness match for my 2004 AWD Suburban. They say the harness has the same part number for different drivetrain Chev vehicles, they have already ordered-in two and they do not match my vehicle’s needs. The search continues.
Does any of this sound familiar to you experts?
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My first experience with AAMCO…… They did a diagnostic on my ’88 GMC C2500….. It had a vibration….. They said they needed to rebuild differential … I questioned their opinion……. I determined it was just a U joint.
That is my opinion of AAMCO.
A decent bidirectional scanner will show the "commanded" gear vs the "actual" gear. That might help with the diagnosis.
