i have a 1999 s10 zr2 and it throwing this p0785 i have replaced the ignition switch and the soleniods in the transmission and check the wiring harness and still have the same problem i can reset the code a couple of times and it goes away but still comes back im pulling my hair out i cant figure out can someone help

 

For any other year apart from 1997, it, most of the time would be the transmission.


Read this, if you're still having problems.

98 blazer p0785 shift timing solenoid malfunction Problem Diagnosis - Car Questions, Answers, and Discussion

 

Never--almost never anyway--change parts based on a code. What you need to do is get an official Chevy service manual. (They can be had cheap on ebay.) NOT a haynes or chilton. The real manual will have a diagnostic procedure to follow to find out what is actually wrong. Unfortunately, some of the procedures--not all or even most-- require the code scanner to command a diagnostic test. If that's the case in this instance, you can hope that whatever the test tests isn't it and do the rest of the other procedure. If none of that is bad then you assume that the commanded test would have turned out negative. It's best to have a scanner that has true Bi-directional ability. Most don't even if they say they do. Most that advertise Bi-directional commands really can only command one test: the evaporative system. The only one that's half way reasonably priced that does is the AutoEnginuity program for a laptop. still looking at $400 or $500. AutoEnginuity® - OBD2 Scan Tool - Professional PC and PDA Diagnostics

BTW, the only way to bleed ABS equipped brakes is with the use of such a scan tool. Bleeding your brakes without commanding the ABS valves to open is pretty much a waste of time.

 

Searching for 'P0785' turns up the diagnostic tree in the thread below which will run through the tests that must be done to get to the root cause of the issue:
P0785 - Shift Timing Solenoid

As Nak mentions, a bi-directional scan tool is required to effectively test the systems without taking the shotgun approach to auto repair. Without a capable scantool, repairs get more time consuming & involved, but can still be done. A mutlimeter can be used to test continuity of the wiring & resistance of the solenoids to see if everything is appropriate.

 

Found out that my problem was with my wiring going down to my transmission i had to pull it out twice but you really have to look so if anyone is throwing seloniod codes down to the transmission check the wiring my truck has alot of miles on it but what had happened is through out the years the wires rubbed together causeing a shorts and unproper voltage to the transmission so before replacing anything check out the wiring harness

 

Good job finding the problem! Visual inspection of the harness is a good place to start, but often the exterior loom doesn't show signs of damage while the wires inside could have been crushed or abraded from vibration. That's where continuity testing, especially across circuits with both ends of the cable disconnected can show faults. Glad you were able to find it quickly and easily!