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Gorilla June 27th, 2010 9:21 PM

HELP!!! OBD II Codes Suggest Transmission/Transfercase Troubles
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<HR style="BACKGROUND-COLOR: #000000; COLOR: #000000" SIZE=1 itxtvisited="1"><!-- / icon and title --><!-- message --><!-- BEGIN TEMPLATE: ad_showthread_firstpost_start --><!-- END TEMPLATE: ad_showthread_firstpost_start -->2001 Silverado Z-71, 4 W/D, Automatic Transmission

Yesterday while pulling boat and trailer from water up ramp with my truck in 4 wheel drive high, the transmission seemed to not engage correctly. I placed transmission in 2 wheel drive and then back to 4 wheel drive high. The truck pulled boat and trailer up ramp but transmission again did not seem to engage correctly and again I returned transmission to 2 wheel drive. I let the truck run while I prepared the boat for travel. When I returned to the cab, the check engine light was on. I installed OBD II code reader and the following codes were activated.....PO 740 (TCC circuit malfunction),
PO 785 (Shift/Timing Solenoid Malfunction), P1860 (TCC PWM Solenoid Circuit).
Please advise me of troubleshooting procedures if applicable or if my transmission is about to take another crap??? Thanks In Advance for Your Assistance! Gorilla
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jeremyt August 1st, 2010 7:53 PM

1 Attachment(s)
I see this problem often. It also happened to my 1999 Suburban. On my Suburban, it was the power circuit 1020 to the shift solenoids. I had trouble codes P0740, P0753, P0758, P0785 and P1860. The tach and speedo did not work either. On the Suburban, there should be +12volts to the #20 fuse on the IP fuse box. If not, the ignition switch needs to be replaced. If so, the 1020 circuit (pink wire) needs to be traced to the tranny (4L60E). My problem was a short in the circuit.... there was 12.7 volts at the fuse box, but only 1 volt with fuse in place. It was grounded, I don't know why it didn't blow the fuse. If power is good to the IP (instrument panel) fuse box, make sure there is power to the circuit at connector 122 @ the tranny, should be a pink wire. The 20-pin connector has been known to go bad. I have attached the wiring diagram for the 4L60E on the Suburban, should be similar to the Silverado. If I can find the TSB for this problem I will post it.

weaponx1979 April 26th, 2011 7:29 PM

97 suburban with same codes/problems
RE: jeremyt....
Hey man. I have a 97 suburban with similiar problems as your 99(tach and speedo dont work when the tranny starts to slip w/codes P1860,P0740 and P0753. I tried your method of putting volt meter to the #20 fuse and got a reading of 11.71V. Do you think the -.29v would cause the ign switch not to send proper signal to the shift solenoids? Im stuck between buying a $155 part or bringing it to a tranny specialist who may not diagnose it right

jeremyt April 27th, 2011 7:51 AM

Quick Diagnostic: If you can remove the lower plastic piece on the steering column, it will reveal the ignition switch on the right hand side. With the motor running, tap the ignition switch a few times with the butt of a screwdriver and see if your gauges come alive. If they do, which they probably will, replace the ignition switch. If not, tranny specialist. Hope this helps!!

weaponx1979 April 27th, 2011 10:50 AM

After a few taps, the Tach came back on but engine light is still on. I'll try a new ignition switch..thanx

JHead84 August 21st, 2014 10:13 PM

I know this thread is old but what do you do if you have already replaced the ignition switch and you still get these codes? I have a friend that runs a transmission shop that said the same thing but now that its replaced he doesn't know. We live 1000's of miles apart so he can't inspect the vehicle. I've got the stuck in 2nd gear problem.

silverado 1500 2001 August 22nd, 2014 9:02 AM

did you dip your axel in water or run through brush ? you might have a little vacuum tube which actuates 2/4 wd at the differential/box. if leaking or loose or sucked water you might get problem. if your connectors got loose or wet you might get an issue. obviously check fluids before towing. ps. main cause of brake rotor warping is running through a puddle after allot of (or hard) braking. put water on those hot rotors and in no time you'll be having pulsation and need rotors turned

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