I have a 99 k1500 suburban with a 4l60e. So i just got a rebuilt 4l60e from a tranny Guy he said he tested all the electrical in the transmission when he rebuilt it. Well after it was installed it is throwing p0740 and p0785 but tranny codes and circuthe problems. He told me to unplug the tranny and cleat the connection which I did and it still throws the codes. The 740 code will come on once I go 45 MPhil. The 785 will come on after that. It will start out in 2nd gear and sometimes shift hard. Also had it go into a limp mode while driving shut it off and restarted it and it worked fine. Don't know what you do I have seen it might be the pcm or the ingition switch. The tranny Guy is positive it's a electrical issue and not the trans

 

Did he "test" the solenoids or replace them?
After 17 years it really is time to replace the solenoids.
Its either exactly what the codes say it is - a bad TCC solenoid and a bad 3-2 downshift solenoid or else the connector to the trans has a lot of corrosion.
When you remove the trans connector you should get many more codes.
You can replace all the solenoids yourself; it will be easier to splice in a new TCC solenoid than replace the entire internal harness.

Just to be sure it is not an electrical problem in the car, locate the trans fuse and using a volt meter make sure it reads more than 12V with the engine running.

 

He checked everthing I. The trans with his tester and replaced what was bad. Like I said I pulled the wiring harness and cleaned it.

 

Every sponsor here replaces all solenoids with brand new ones, and I'm pretty sure a brand new wiring harness. IMHO that is the correct way to rebuild a trans. They can fail or at least begin to malfunction in ways that a simple ohm-meter test will not detect.
1. First make sure you have 12V+ going to the trans by checking on the fuse.
2. Search for "4l60e solenoid kit". I see complete kits with the full internal harness for around $120. You can install it yourself from underneath the car.

 

 

Pretty sure that when people have problems with the ignition switch the trans isn't getting 13.7 volts, or even 12V.

 

thanks for sharing

 

Low battery voltage poor connections or grounds can cause erratic solenoid codes .

 

Im having the same problem with a 2005 Silverado 1500 2wd it won’t shift out of 2nd replaced trany twice replaced ecm replacer torque converter and the truck is still not shifting out of 2nd I have waisted about 2200 for nothing has anyone solved this problem yet ?

 

ignition switch
happens all the time with this era gm vehicles

all the power for the trans has to run through the ignition switch. I've had them check fine with a volt meter (because a volt test has no load on the circuit)
but still not work.
Change the ignition switch...viola it works perfect again.

could also be a fuse or broken wiring...but the gist is...likely no power to trans

 

Just replaced ignition switch and truck is the same any other ideas ?

 

You should start your own thread with all of the details about your trans.