Yeah, it sounds like you have a short or the solenoid driver is “leaking” to ground.

@@siuautomotive Sure enough, the B solenoid wire was intermittently grounding to the chassis. The sharp edge of the spring clip that holds the ECM had worn through the bottom of the corrugated split conduit on the wiring harness and worn through the B wire’s insulation and some adjacent wires’ insulation. So my “transmission problem” was a wiring problem all along. Live and learn.

Glad you found it!

I had a rub-through on a 99 safari that drove me nuts years ago! Turned out to be under the ecu where the loom passed the PS line. Damn near rubbed through the line too! @@testmcgee9230

That code sets when the computer doesn't see the voltage that it's expecting. When the solenoid is commanded "off," the voltage on the wire going to the TCM should be at 12 volts. This is because the solenoid is fed power from a fuse and the ground is provided by the TCM. When the solenoid is off, the transistor in the TCM is open. And since no current is flowing when the TCM has that transistor open, 12 volts will be present on the wire going to the TCM. When the TCM turns the transistor ON, current will flow and voltage will then drop across the solenoid (when turned completely on, that solenoid is modulated). If there is an open in the wiring, connector, or solenoid, the TCM will see "zero" volts when the solenoid is commanded off. It knows that's a problem so it sets the DTC. It'll also set the DTC if the wire between the solenoid and TCM is grounded, but since you say the TCC never engages, it's probably not that. If I were you, I'd monitor the voltage at pin 1 of the TCM. It should be 12 volts when the TCC PWM solenoid is commanded OFF. If you see low voltage, than you have a bad connection or an open somewhere. It's always possible that you have a bad TCM. I do have a video on basic transmission electrical that explains a bit about these solenoids and their control and I give examples.

​@@siuautomotive I'll check the harness for voltage etc. I'll let you know and post my finding for others to use in case they have the same issue. Thanks for the reply!!

@@siuautomotive 98

@@siuautomotive Update: Finally got the P2764 fixed! After dropping the tranny for a Rebuild. While everything looked ok inside just over 100,000 miles no burnt clutches etc...just pistons that looked slightly dry and probably see better days, I replaced everything. Mainly clutches and I also bought a rebuilt torque converter for $140, bearings all checked ok. Valve body seemed ok. Put tranny back in...still was in limp mode! Just had 2nd, 3rd gear. So With everything replaced checked, the only thing i figured it could be was the computer. Wires at the torque converter clutch pressure control solenoid check out ok also. So Figured gotta be the computer! So got one off e-bay programed for a trailblazer, installed it followed the instructions and bam!...started, dropped it in gear and would you know 1st gear!! Then it went to 2, 3rd, 4th and then overdrive (5th). So it was the computer! Someone had worked on it before I got it and shorted wires and the valve body. I had one solenoid that was burnt, I replaced it and never thought anything of it -- that was my sign and i looked over it, A shorted computer. So all is good one year later its finally fixed! (Weird thing is, it actually shifted a few good time when I first got it but one day just stopped so I thought the computer was probably ok). Hopefully someone can use this info to help them out. Man so much research went into this and i was determined to fix it. It runs like new now. So now I have a $2,500 tranny (the cost of a rebuild one) for about $425. That's a good day for me:)

My guess is you have a short in the harness between the TCM and the trans. You already ruled out the internal harness by changing it. A TCM couldn't cause the problem, because it's on the ground side of the solenoids. You'll probably find something rubbing through your engine/trans harness somewhere causing an intermittent short. Nothing hydraulic can cause a short in your solenoids. When the trans is shifting, it's probably torquing the driveline and causing the wire to touch ground.

The current is effected by the pintle movement very slightly, but unlike an electrical motor, there’s no counter electromotive force to speak of. The current flow is really a function of its coil resistance.

Are you using a commercially available standalone system? If so, I’d suspect there’s instructions. I’ve never installed one, but I would think that they use a throttle position sensor as input to control line pressure solenoid pulse with modulation.

@@siuautomotive No, seen a lot of people using switches to turn solenoids off and on. The problem with that is it goes to full line pressure, is there anyway that I could use something external like a rheostat to control line pressure? And if so where would I hook it up at? There is a guy on Ebay selling controllers for full manual mode, stand alone system pretty cheap,$129.00 but he doesn't talk about line pressure.

I think that's the PCM to prevent overheating

It can, but I don't think a 1" change will have too much of an effect. The speedometer will be off and the shift timing will not be based on "real" vehicle speed, since it uses a speed sensor off of the transmission or transfer case. It'll probably be off only 2mph at 60mph. Randy's worldwide has some calculators on their website that might help: www.randysworldwide.com/calculators/tire-height

@@siuautomotive Thankyou

The only clutch that needs to apply for first is the forward clutch. I wonder if you have a cracked forward accumulator piston since it’s likely made out of plastic. It’s the accumulator piston located in the valve body.

@@siuautomotive i checked the accumulator piston looks good..but i couldn't remove the piston.. And when i shake it gives a metal sound i think it's coz of the small spring but not sure.. I'm thinking to put sonnax pinless piston, what r your thoughts about that?

When you pull that steel plate off, the spring should come out. Then grab the accumulator with a pair of snap ring pliers that expand large enough to grab the inside of the piston and pull out. The aftermarket accumulator work well, but many just toss the plastic one and use an aluminum one.

@@siuautomotive ok I'll remove the accumulator and see.. Mostly I'll go for pinless accumulator.. Hope it'll solve my shift problem🙂.. Because i can feel the throttle response abd rpm change when i switch from N to D.. Thank you do much for your replies.. 👍

@@siuautomotive I'm having a similar problem but my unit is rebuilt with the aluminum accumulator pistons wondering what could cause this also

The max line pressure is determined by the pressure reg spring, afl pressure. And the size of the boost valve. So tuning alone cannot increase max line pressure. You can alter pressures between min and max with tuning by changing your pressure control solenoid amperages and adjusting desired shift times.

@@siuautomotive i have 6.0l 2002 drive by cable tunned MAF deleted My 4l60e has lime pressure 60psi max on all gears and all the ways except R has 85psi 2 n 3 n 4 start to slip from 2000 rpm 1 n R verry gòod

If you unplug the trans connector you can verify that the pump can generate pressure. With the engine running in park and the connector disconnected, you should have 200+psi. If it’s still low, then there’s a problem in the trans. If it’s high, there’s a problem with the tune or computer.

I’m sorry, I don’t have any of those transmissions :(