4l60e acting up, it's doing the normal not shifting from 2-3 bullshit. Just revs like it's in neutral.
Instead of scanning for codes etc I just bought a used transmission. After installing it and driving 20 miles it starts doing the exact same thing which leads me to believe it's electrical.
I know these transmissions are junk but what are the odds that one of them would be doing the exact thing as the other??
Is it on the vehicle side of things or...

Truck is an 03 Sierra btw

 

The PCM controls the line pressure and if the pressure to too low under high throttle, the trans will slip.
A defective MAF or TPS can cause a trans to slip; this is very bad because the friction plates that quickly wear out.
With a scanner, scan for codes and confirm that the TPS value goes near 100% with the pedal to the floor.

 

With the electronic TB do I have to change the whole TB or can I just change that black box on the side?

 

Whats wrong with the tb?

 

With a little experience, the "nice" thing about these computer controlled cars is that with a good scanner the car basically tells you what is wrong.

So don't go replacing parts until you run a scanner.

 

I was referring to the TPS, it's all one piece with the DBW TB

 

Like mrvedit said, don't just throw parts at it.

The easiest thing to do would be to disconnect the wiring harness from the transmission. It will be stuck in third, that will sure tell you if third works or not.

I just sold a rebuilt 4L80E to a guy I work with and it did the same thing as his old one, the problem ended up being the ignition switch. Actually he said a wire on the shift lock solenoid but he already ordered the switch. So things can be weird, especially with DBW vehicles. It could be the gas pedal.

 

So regardless, a scan should tell me what's wrong?
Can I go to my local part store and have them plug it in or does it need to be a transmission shop?
I don't know if there is a difference in the scanners they use or not.

 

A parts store should be able to do it.

 

No, a scan most likely will not tell you what is wrong. But scanning it *may* provide information that is helpful with diagnosing what is going on.

As mentioned above, unplug the round electrical connector and then start the engine and put it in D4 position and try to move the vehicle. If the 3-4 clutches are not burnt, it will try and move forward albeit very sluggishly. It is important that you NOT step on the gas hard, and DO NOT try and drive it down the road this way. You are just doing a test to see if the 3rd clutches are healthy enough to engage and move the vehicle. You need to perform this test while the trans is at operating temperature. Cold testing may give false results.

There is a high probability that you purchased the transmission and the 3-4 clutch pack was already worn out. This is one of the most common failures, if not THE most common failure that we see on these units. Sonnax Smart Tech drum gives you the option of getting 10 3-4 frictions in that drum, and along with some other upgrades almost eliminates the dreaded 3-4 failure-except in high/higher horsepower applications.

 

While the OP's problem probably is a 2nd trans with a worn 3/4 clutch, I try to encourage everyone to scan for codes before replacing parts (or entire transmissions) and ideally before even posting here.

Kawabuddy, you are obviously a pro who knows how to quickly diagnose a trans problem. However most members here (me included) don't have that experience level and therefore need a simple "flowchart" to figure out common problems. I always suggest starting with a scan and then hooking up a pressure gauge.

 

I haven't unplugged this transmission but I did unplug the first one that was giving me the same problem. With the transmission unplugged it pulled itself fine which is another reason I don't believe it's the 3-4 clutches.... but I could be wrong. I still haven't done a scan because the nearest town is 20 minutes away, even longer while driving in 2nd gear.

 

it might be cheaper to buy a scanner than to keep buying trannies

 

Yeah no kiddin.... I went and had it scanned, no codes. I guess I'll get this one rebuilt rather than buying another used one

 

If you have a scanner, or have access to a scanner, there is another test that you can perform before you move forward with replacing the transmission.

Hook up a scanner (NOT a generic code reader) and access trans data. Now, jack rear wheels up off the ground and support axle on jack stands. Now, find the data stream that shows what gear the computer is commanding. Put car in gear and "drive" it this way watching the screen to see if the computer is commanding 3rd gear. If it is an EXTERNAL problem-meaning computer, or some external sensor, the computer will never command 3rd, and the trans will never try to go into 3rd or 4th gear.

The flip side of this is that if the computer is commanding 3rd gear, and the trans is not going into 3rd gear, you now know for certain the problem is inside the trans. The downside to testing this way is that the clutches may hold and accelerate the rear wheels into 3rd gear when there is no load on the drivetrain, but when attempting to actually drive the car the clutches will not hold. So, if you think it is going into 3rd, and the computer shows it is commanding 3rd, you need to punch the gas pedal really hard to see if it slips, or stand on the brake like you are power braking while still holding the gas to see if it slips while in 3rd gear. It's not scientific but if done right it is an effective way to diagnose the problem.

Mrvedit, it is rarely necessary to plug in a pressure gauge to diagnose problems like this. There is NO conclusive data to be gotten from a pressure test that would supercede the results of a good scan (data & codes), in addition to a road test, and fluid level & condition inspection. In this case if his 3/4 clutches are burned, the unit is still going to show the correct pressures, but it still will not hold in 3rd or 4th due to the surfaces of the frictions being compromised. So pressure testing in his case may only add to the confusion. Also, if his computer is not allowing the trans to shift into 3rd, he would not be able to get pressure readings for 3rd, 4th, or lock-up anyway. He already knows that 1st & 2nd work, so knowing what the pressures are in those ranges is not likely to further his diagnostic. We know the pump, torque converter, & fluid level are working to produce enough pressure & volume, to move the car in 1st & 2nd, so there *should* be enough for 3rd/4th/lock up. See what I mean about a pressure test being inconclusive? Most times a pressure test will only confirm what you already know-that there is a problem inside-and that whatever time you spent performing the pressure test could have been spent pulling the unit back out which has to happen anyway IF the compute is commanding the higher gears and the trans is just not going into them.

If the OP does not have access to a scanner, I can give him a simple way to test the signals coming out of the computer to see if it is commanding 3rd gear. Will need either a test light, of DVM, or DMM.