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Old 03-24-2008, 09:06 AM   #1
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Default PO785 on a 4L60E

Guys and Gals

I really apologize if this question has been asked before but I have searched and not found the answer. I have a 97 Chev truck (4L60E) that I got the PO785 “Shift Solenoid Malfunction” error code last week. When warm it starts in 2nd or 3rd and will not shift into 4th and the converter will not lock. I went to the Chev house and they sold me two solenoids (identical) that think control the 1-2, 3-4 shift. They are located side by side at the front of the transmission. I replaced them and I have the same problem again and same error code. Note when it is cold everything works great. Only when it is warm does it not shift correctly.

Can anyone help? Did I replace the wrong solenoid?

Thanks.
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Old 03-24-2008, 09:32 AM   #2
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PO785 Is a code for the 3-2 solenoid its located on the drivers side front. If this is the solenoid you replaced then you will need to start looking for electrical issues, Try unpluging the pluging back in the round plug over passengers side pan rail . Look at all wiring coming down from engine compartement .

Circuit Description with 4L60-E / 4L65-E Automatic Transmission
The 3-2 Shift Solenoid (SS) valve assembly is a normally-closed, 3-port, on/off device that controls the 3-2 downshift. The solenoid attaches to the control valve body within the transmission. The solenoid receives ignition voltage through circuit 239. The Powertrain Control Module (PCM) controls the solenoid by providing a ground path on circuit 687. During a 3-2 downshift, the 2-4 band applies as the 3-4 clutch releases. The PCM varies the timing between the 3-4 clutch release and the 2-4 band apply depending on the vehicle speed and the throttle position.

When the PCM detects a continuous open, short to ground or short to power in the 3-2 SS valve assembly circuit, then DTC P0785 sets. DTC P0785 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
  • The system voltage is 8-18 volts.
  • The engine speed is greater than 450 RPM for 5 seconds.
  • The engine is not in fuel cutoff.
CONDITIONS FOR SETTING THE DTC
DTC P0785 sets if one of the following conditions occurs for 5 seconds:

Condition 1
The PCM commands the solenoid ON and the voltage feedback remains high (B+).

Condition 2
The PCM commands the solenoid OFF and the voltage feedback remains low (0 volts).

ACTION TAKEN WHEN THE DTC SETS
  • The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
  • The PCM commands a soft landing to third gear.
  • The PCM commands maximum line pressure.
  • The PCM inhibits TCC engagement.
  • The PCM inhibits fourth gear if the transmission is in hot mode.
  • The PCM freezes shift adapts from being updated.
  • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
  • The PCM stores DTC P0785 in the PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met
As you can see PO785 happens when the 3-2 solenoid circuit is open or shorted. Its and elctrical code.
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Old 03-25-2008, 08:28 AM   #3
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Thanks, I replaced the 3-2 solenoid and I have driven about 40 miles and it is working great. I think that was the problem.
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Old 03-25-2008, 08:39 AM   #4
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Your welcome any time
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Old 10-24-2008, 01:36 PM   #5
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Default what is this code (shift timing solenoid)

do yall know what this is, ans what pin in the pcm, i may not have this hooked up right, bu8t keeps throwing the code, the only thing is have acutaly driven the car so dont know if the thing will even shift, i done all wireing my self,
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Old 10-24-2008, 02:19 PM   #6
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Do you happen to know the number of the code PO????
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Old 10-24-2008, 10:53 PM   #7
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Default what is this code (shift timing solenoid)

no but ill get, im working right now and didnt think about it at the time, dont know if diablo gives numbers but ill see
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Old 10-24-2008, 11:02 PM   #8
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well its the po785 code,what this whole thread is about
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Old 07-21-2009, 10:41 PM   #9
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PO785 ! ! !
Heres some helpful info dealing with the 4L60E Tranny and the PO785 Code. eRanch had the exact same problem I did, however, after I replaced the 5 solenoids,(PWM, LocK-up, 1-2 shift and the 2-3 shift,( these are identical solenoids) and the 3-2 Control Solenoid) plus the Pressure Manifold Switch, I still had the same problem. Ran fine when cold. Warmed up, and no Lo gear or 4th and over-drive. Only thing left to replace was the ECM.
It cost me $113.00 + 40.00 for programming, and problem is gone, and Tranny works just like it did when it was new.
If you have a 1997 Chevy or GMC and trouble with the Tranny and a PO785 code,
remember this info. It might save you a lot of time on your back looking at the underside of a 4L60E. I also put a drain plug on the pan to make fluid changes easier.
One more tid-bit of info.....the PWM solenoid is different from the 3-2 control solenoid but most suppliers list them as the same. The difference is the last letter of the part number.....Note: D74418e is the PWM solenoid....D74418EA is the 3-2 control solenoid.
The measured resistance on the D74418e is 5-15 ohms, on all the other solenoids the resistance is 20-25 ohms. Thats important to the computor's I/O.
I hope this info is helpful to others with the same problem, and eRanch may have trouble again with his 4L60E, so, just change the ECM.
Good luck everyone, and I hope I save you a tranny rebuild @ $2000.00.
Bob F.

Last edited by bfell281; 07-21-2009 at 10:50 PM..
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Old 03-27-2013, 05:31 PM   #10
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Hey there-
My trans failed so I bought a 4L60E from similiar vehicle that had been T-boned and I had the trans shop install it for me, because I just had surgery. This owner of the wrecked vehicle had the trans rebuilt about a month before the accident.
After the install the trans wouldn't shift from first to second. The trans shop replaced the 1-2 shift solenoid. I drove it home, no issues. I drove it the next day and it slammed from 1-2 & 2-3 after it warmed up. I plugged in my Snappy scanner and I had no codes. I drove it today and it slammed when shifting again and turned the SES light on. I scanned it and I got codes P0785 - Shift Timing Solenoid "A" & P0894 - Transmission Component Slipping. I know the PCM commands maximum line pressure when P0785 is set, so should I assume its the solenoid and replace it?
Does anyone have schematics?
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Old 03-27-2013, 08:04 PM   #11
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That is consistent with a bad 3-2 downshift solenoid. Keep in mind it could also be bad wiring inside the trans or a bad connection on the trans connector, but it usually is a bad solenoid.
This solenoid is located on the rear driver's side of the valve body, near the shift linkage. You only need a small flat screwdriver to pull out its clip to replace it.

Here is a detailed electrical schematic:

http://www.msgpio.com/manuals/mshift/wiring.html

Is that what you want?
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Old 03-29-2013, 09:19 PM   #12
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Yes, thanks!
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Old 04-05-2013, 09:58 AM   #13
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Default 3-2 shift solenoids

i have a po785 error code on my 1998 Chevy Astro van. I dropped the pan and went to replace the 3-2 solenoid and found that it has 2 very similar looking 3-2 shift solenoids....they look identical except one has a grey connection cap and the other has a red connection cap. These solenoids are different thean the square 1-2 2-3 shift solenoids. Any help?
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Old 04-05-2013, 06:49 PM   #14
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The 3-2 shift solenoid is in the rear driver-side corner, very close to the shift linkage.
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Old 04-05-2013, 11:07 PM   #15
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Thank you, replaced the 3-2 along with 3 other solenoids and the van works great! What a relief not having to rebuild the whole thing.
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Old 07-13-2013, 02:36 PM   #16
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im having similar problem,but i replaced all solenoids and still my tranny is stuck in third,heres my post Need help with my 4l60e
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Old 07-13-2013, 02:36 PM
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2nd, 4l60e, control, dtc, ground, malfunction, p0785, po785, problem, shift, solenoid, strts, timing, warms, working


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