OK, so it's not quite an LS1, but's it's GM, and has a Vortec engine. That's not the problem, though.

I'm a suspension shop, but I took a tranny job as a favor to a freind

It has a 4L60E mated to a 5.3L. It's a '99, and has the large-style converter. I replaced the transmission after the original spit out a bearing, and then started having a weird problem (at least for me). When I first put everything back together, there was nothing. Absolutely zero. When you drop it into gear, it would sound like the engine was loading up, but hitting the gas pedal resulted in nothing. No go. Revving it up to around 4500 RPM will get the speedo to show around 5 MPH, and if the back wheels are in the air they will move (just a little, and can be easily stopped just by touching them). So, you say, it's gotta be the torque converter! That's what I said, too. I'm on TC #3 right now. Same symptom. So, it must be the tranny, then. It was used, after all. We all know that sometimes you get a lemon from the auto recycler. I'm on tranny #2 right now. Same symptom.

Then the customer says that the Transfer case has been acting up for quite some time, now. OK. Brand spankin' new T-Case straight from GM. Same symptom.

So I go buy a shiny new Snap-On scan tool and hook it up to the computer to see what's going on inside.

Looks like everything is ok, except...there's a parameter called 2-3 downshift, and the reading says "YES". Also, no matter what range the lever is in, the tranny says it's in first, except when it's manually placed into second. The gear selector indicator is reading correctly, and the scan tool says the switch outputs for the selector switch are correct.

I've been messing with this thing for close to 3 weeks, now, and I need to get it out of my shop. I'm sure I'm miising something obvious, but damned if I know what it is.

Other points to note:

**It has 11+ quarts of fluid in it (That brings the dipstick to exactly normal after letting the tranny warm up for 15 minutes or so). It's had as much as 13 quarts in it, with no noticeable change in the fluid, except the dipstick reads way high.
**All of the connectors are in the right place and connected.
**It has the Automatic 4WD feature

I know I'll be smacking myself in the head when I finally get it figured out, but right now it's driving me nuts. If anyone has seen this before of knows where I might look next, that would be very helpful.

Thanks!

Pete Griffith
Owner, Professional Autoworks
Murrieta, CA

 

Do you have a pressure gauge? If you do then try monitor the pressure on the tranny. At an idle, pressure should be about 90-110 PSI. It sounds like the pressure valve is stuck.

Kevin Steele
TCI
Product Engineer

 

Hi Kevin, thanks for your reply.

I agree with your idea about the pressure valve, except...is it electronically controlled?

This is the second replacement transmission in the truck with the same exact symptom, and the third torque converter. The second tranny was certified good, and I bought the TC brand new in the box.

My instincts say it has to be electronic, but even with the scan tool I'm stepping in way over my head when I start going there. I'll be the first to admit that electronically controlled trannies scare me (that alone should have stopped me from taking this job, but noooooo.....I had to say yes...go figure).

An yway, thanks for your reply. I've been all through my AllData discs trying to get info on this, but so far no luck. I'll keep trying, tho.

 

To see if its electronic, unplug the case connector. The transmission will default to 3rd gear with the selector in any forward range.

 

First check that TC is all the way in, otherwise the pump won't go and will get broken;

Second, hook up oil pressure guage to line tap on side of case and check for pressure (about 150-230 psi); if no pressure, could be loose or broken pressure control solenoid;
to tell if you got any pressure from the pump, undo either one of the cooler lines and measure how much fluid comes out from 30 seconds of idling in Park; should be about 2 to 3 quarts in 30 seconds; if you get less than this, then the pump is not working; if you do get this amount, then problem is not in the pump;

Third, with your scan tool, display the following:
a. Turbine Speed and see if it looks anything like engine speed; if not, then TC is not all the way in and is broken;
b. Trans. Force Motor Duty Cycle (TFMDC); this is the pressure control solenoid duty cycle that the PCM is commanding; should be about 70% or something similar; should not be more than 90%;
c. Current gear; this tells you the commanded state of the two shift solenoids (I think this is what you are looking at ("in first always except when in second")); this is Not the gear lever position;
d. PRND321 signal; this tells you what position the gear selector lever is in; the PCM reads this from the fluid pressure switch module on the bottom of the valve body; this has to match the gear lever position; if not, then the wire harness may be pinched (explains your "neutral"), or the pressure module is not working;
e. TFT (trans. fluid temp); if this looks very abnormal, then you got an open or short in the harness, or the wrong trans. for this PCM and harness;

Other info:

The pressure control solenoid controls pressure as follows:
* open circuit (full off) gives maximum pressure;
* short circuit (full on) gives minimum pressure (I'm not sure how low this pressure goes, but the trans will still engage and go, but the clutches may slip under load);
* the duty cycle to the PCS is inversely proportional to the pressure required
(high duty cycle gives low pressure, and vice-versa); sharp increase engine RPMs should cause this duty cycle to go down;

The 3-2 downshift solenoid duty cycle only matters when a 3-2 downshift occurs;

I don't own a shop (my dad used to, though), but I hope you get it figured out; best of luck man;

 

Please let us know how it goes as well. I'm curious as to what is wrong. I'm sure many others would like to know as well.

 

update (still not working).

Since my last post I have checked the pump output. It was good. The cooler line output pumped out about 3 and a half quarts in a little under 30 seconds. I'll call that good. I suspected a blocked tranny cooler return line, and replaced that (and the cooler). I did this because the original reason why it was in my shop in the first place is because the tranny ate itself (and then the idiot drove it home in reverse when he lost his forward gears). Still nothing.

I went back to my trusty scan tool and went through all the parameters again.

The pressure control solenoid seems to be working properly. I am able to run the functional test and get the proper feedback response.

The TFT sensor is reading correctly.

The PRND encoder circuit seems to be working fine. It doesn't show any invalid positions, and responds to the shift lever position, correctly displaying the selected gear both in the dash and on the scan tool.

There is no "Trans Force Motor Duty Cycle" parameter available to me (Using Snap-On MTG-2500 scan tool with troubleshooter).

There is a parameter called "Park Switch" which always shows closed no matter what. This parameter only shows up when looking at the parameter list for the Automatic 4WD system. It is not available under the transmission system parameter lists. According to my handy Snap-On Domestic Vehicle Parameter Definition Manual, this should only be closed when the vehicle actually is in Park or Neutral. I'm tracking this one down next. Hopefully this will work.

Still trying!

Pete Griffith
'01 Suburban 5.3L
'00 Jeep TJ, far from stock
'87 BMW 325ic
'71 Caddy Sedan DeVille 472/TH400/funky Buick/Olds/Cadillac 9 3/4 rear end - Looks like a deformed 14-bolt
'69 Chevy Pickup (Heavy Half) 350 High Perf/TH400/12-Bolt

 

what happens when you completely unplug the transmission from the PCM like previously suggested?

 

When I disconnected the harness, the computer threw all of the expected DTCs, but still nothing. The scanner indicated that 3rd was commanded, but of course with the harness disco'd there was no feedback.

When I reconnected the harness, I had to manually clear the codes, and then there was nothing again. It is not throwing any DTC's, and there is no MIL commanded.

I dunno. I pushed it back in the corner again. I have a long block swap on a big 3/4 ton Chevy truck that I have to deal with before Monday, so I switched gears.

 

hmm.. if the trans doesn't go when you unplug the harness then I'm gonna say its something wrong with the trans. (that is if the trans defualts to third gear with no harness)

 

Yeah, that's my assumption as well. It just doesn't make sense, though. This is the second tranny and third torque converter, all demonstrating the exact same symptom. Logic says it can't be the tranny, but we all know how far that goes...lol

Thanks for all the input!

 

99yukon,

Yes, the pressure is controlled by the force motor but the pressure regulator valve feeds the force motor. So, if the valve sticks open, then the motor force has no pressure to bleed off. Does it have the same symtom in reverse? Are you sure the stator splines on the pump are good?

Kevin Steele
TCI
Product Engineer

 

"There is no "Trans Force Motor Duty Cycle" parameter available to me (Using Snap-On MTG-2500 scan tool with troubleshooter). "

TFMDC sometimes comes under various different names (something to the effect of commanded line pressure duty cycle or something), but I can't remember all of them.

Kevin Steele (TCI) is right about the press. reg. valve; do you get pressure from the line pressure tap at the side of the case...?

Collecting the facts together:
a. the PRND321 signal matches the gear lever position (TFP switch assembly is working);
b. the current gear signal says 1st always (means solenoids A and B are in 1st gear position), except when manual 2nd is selected in which current gear indicates 2nd gear (sols A and B in second gear position) which is correct (i.e. used for 2nd gear starts);
c. it neutrals no matter which gear range selected;
d. 3.5 quarts in 30 seconds;
e. TFT is in range;
f. second trans. and third TC and same problem;

As Kevin Steele (TCI) said check stator shaft splines and peek inside pump between seal and stator shaft with flashlight to see if there's metal fragments;

hummmn, [somewhat off the wall] check to see if the drive shaft yoke splines are ok and is the diff ok (no, never mind [I'm just thinking out loud] you would've heard ugly noises);

What was your customer's original complaint...?

 

Whats the latest?

 

"I am able to run the functional test and get the proper feedback response."

Is this the test where you use the scan tool to command the line pressure while viewing the oil pressure guage that you attached to the line pressure tap...?

If so, then the pressure regulator is working fine, and we're all stumped on this problem.

 

Very interesting symptoms. ...

First off, you said with 10qts or so of fluid in the trans the fluid level gauge read properly and when put in gear the engine seemed like it loaded some ... your hydraulics are working.

I'm thinking you're not connected mechanically to the T Case output shaft. ... With trans in park, does the mechanical connection from the T Case output reflect this? If yes then focus on trans. If no then focus on T Case.

Let us know ... Ron

 

Whats the latest??