Need help, 1800 miles from home, and getting DTC p0785!!!!
06-14-2012, 12:09 AM
#21
Well, it's back. 
After driving the car when I got back from Texas, it started doing this again. All the flow charts I've looked at end in 'replace PCM', so I did. Problem solved for a couple more weeks, but back yet again. I'm really not even sure where to look anymore. I've replaced the solenoid, PCM several times, flashed different tunes into it, and ohmed the wire between the "s" terminal on the trans connector and the PCM connector, which checked out ok. About the only thing I haven't done is replace the valve body as someone suggested earlier, but this trans only has about 64k on it, could the 3/2 valve bore really be worn that bad already? I mean I realize anything is possible, but just seems like too low of mileage for that sort of thing?
I don't think I've ever been quite this stumped on a swap before????
After driving the car when I got back from Texas, it started doing this again. All the flow charts I've looked at end in 'replace PCM', so I did. Problem solved for a couple more weeks, but back yet again. I'm really not even sure where to look anymore. I've replaced the solenoid, PCM several times, flashed different tunes into it, and ohmed the wire between the "s" terminal on the trans connector and the PCM connector, which checked out ok. About the only thing I haven't done is replace the valve body as someone suggested earlier, but this trans only has about 64k on it, could the 3/2 valve bore really be worn that bad already? I mean I realize anything is possible, but just seems like too low of mileage for that sort of thing?I don't think I've ever been quite this stumped on a swap before????
06-28-2012, 09:39 PM
#22
Fixed. Shorted trans wire to ground caused issue. Good troubleshooting Eric. Finalized tune tonight and all is good. Thx for letting me play. Let me know what your mpg is after your next trip and can't wait to help tune on the next several projects. ;-)
06-07-2015, 11:10 AM
#23
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I've got a P0785, I've pulled pan, replaced all solenoids (except TCC), harness looked good, but when the transmission is hot, I get the error code.
PCM or Wiring short is now my guess. Engine/Transmission are a swap into a 3rd gen camaro...came from a 98 Firebird.
06-07-2015, 08:38 PM
#24
I know I'm bringing this back from the past. But where did you discover the shorted wire?
I've got a P0785, I've pulled pan, replaced all solenoids (except TCC), harness looked good, but when the transmission is hot, I get the error code.
PCM or Wiring short is now my guess. Engine/Transmission are a swap into a 3rd gen camaro...came from a 98 Firebird.
I've got a P0785, I've pulled pan, replaced all solenoids (except TCC), harness looked good, but when the transmission is hot, I get the error code.
PCM or Wiring short is now my guess. Engine/Transmission are a swap into a 3rd gen camaro...came from a 98 Firebird.
06-07-2015, 09:31 PM
#25
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My short was in the engine harness. To be honest I still don't know where it was shorted at exactly. I was checking for continuity on that wire, and it had had continuity to ground at times. When I moved the harness to get a better look at it, I lost the short to ground. So, what I ended up doing was running a complete new wire from that pin on the PCM connector to that pin on the trans connector plug and it's been fine ever since. I still cant understand how the wire could randomly short to ground inside the factory loom though. Hope this helps.
I'm going to have to dig to see if I can trace where the "S" wire from the cannon plug on the transmission connects to the PCM...you wouldn't happen to know off hand would you?
06-09-2015, 09:11 PM
#26
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Ok - got to test drive the car some (obviously still broken) but I confirmed that it's "broken" the way it was before the incident (I initially wondered if it was acting different/worse) since I was getting an immediate P0785 code as opposed to the delayed code. I've been able to attribute that to the change in temperatures, and the trans reaching operating temperature sooner.
So the code is consistent, anytime the transmission is warm and the car is running the code is displayed, the shifts become firm, and the transmission will only downshift when commanded by the shifter (no kickdown obviously).
I got the car back in the air, checked the transmission harness at the transmission, seems very tight. Sadly, it's also a very tight squeeze to reach in the transmission tunnel. Tomorrow after everything is cool, I might try to wedge it out, if not I'll have to lower the transmission some to reach it.
I know I need to ID the "S" terminal on the transmission cannon plug, but does anyone have the pin-out for this wire @ the PCM? I'll plan to put the multi-meter on it to check continuity...or verify that the wire is grounding. I'd love for this to be the problem, as it involves running a new wire, as opposed to replacing the PCM or even the harness internal to the pan.
I called myself "looking" from broken wiring in the pan, but didn't see anything. But the only way I could check continuity there is to remove the pan again...correct?
So the code is consistent, anytime the transmission is warm and the car is running the code is displayed, the shifts become firm, and the transmission will only downshift when commanded by the shifter (no kickdown obviously).
I got the car back in the air, checked the transmission harness at the transmission, seems very tight. Sadly, it's also a very tight squeeze to reach in the transmission tunnel. Tomorrow after everything is cool, I might try to wedge it out, if not I'll have to lower the transmission some to reach it.
I know I need to ID the "S" terminal on the transmission cannon plug, but does anyone have the pin-out for this wire @ the PCM? I'll plan to put the multi-meter on it to check continuity...or verify that the wire is grounding. I'd love for this to be the problem, as it involves running a new wire, as opposed to replacing the PCM or even the harness internal to the pan.
I called myself "looking" from broken wiring in the pan, but didn't see anything. But the only way I could check continuity there is to remove the pan again...correct?
06-26-2015, 04:39 PM
#27
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So I had an extra 98 LS1 PCM sitting around from a spare engine I purchased recently and decided to use it to test. Sadly, that PCM hadn't been programmed for the car, and I had to purchase a LS1 VATs bypass module (tried building one before i bit the bullet and purchased it).
Well, after getting the bypass unit hooked up and finally getting the car started I was able to verify that the code I originally had P0785 (3-2 shift solenoid) was no longer storing. However, in addition to all the codes you'd expect from an untuned PCM, I received P0753 and P0758 (Shift Solenoid A/B Electrical). Wondering if this is related to the computer being in limp mode due to the EVAP system, lack of rear O2 sensors, and a misfire on cylinder # 1?
Well, after getting the bypass unit hooked up and finally getting the car started I was able to verify that the code I originally had P0785 (3-2 shift solenoid) was no longer storing. However, in addition to all the codes you'd expect from an untuned PCM, I received P0753 and P0758 (Shift Solenoid A/B Electrical). Wondering if this is related to the computer being in limp mode due to the EVAP system, lack of rear O2 sensors, and a misfire on cylinder # 1?
06-27-2015, 09:36 AM
#28
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This web site has a lot wiring info that may help.
http://www.lt1swap.com/index.htm
I found this by doing a search. Credit goes to Performabuilt.
https://ls1tech.com/forums/automatic...785-4l60e.html
PO785 Is a code for the 3-2 solenoid it’s located on the driver’s side front. If this is the solenoid you replaced then you will need to start looking for electrical issues, Try unplugging the plugging back in the round plug over passengers side pan rail. Look at all wiring coming down from engine compartment.
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 electrical code.
http://www.lt1swap.com/index.htm
I found this by doing a search. Credit goes to Performabuilt.
https://ls1tech.com/forums/automatic...785-4l60e.html
PO785 Is a code for the 3-2 solenoid it’s located on the driver’s side front. If this is the solenoid you replaced then you will need to start looking for electrical issues, Try unplugging the plugging back in the round plug over passengers side pan rail. Look at all wiring coming down from engine compartment.
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 electrical code.
07-04-2015, 11:16 PM
#29
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Thanks!
I ended up finding this article. Link
And using it, did some more troubleshooting on the transmission. Earlier in the week, the transmission was acting very strange, as if it was dragging the E-Brake when moving forward...reverse seemed to work ok, but the car had a lot of shuddering. I noticed the transmission fluid was low (even though I thought I topped it off when I replaced the filter/solenoids) so I topped it off, but the problems persisted.
Ended up following the testing procedures listed in the link above, and confirmed operation of the 1-2 Shift Solenoid, 2-3 Shift Solenoid, and 3-2 Shift Solenoid. I then swapped in my backup PCM again and fired it up. Transmission was shifting normally for the first time in a couple months, and engine was running beautifully. Took the car out for a test run, all was well...repeated later than night. And this morning I took the car for about a 30 minute drive...willing to say the problem is solved (although I still need to get the computer setup to remove the emissions codes and VATS). The only thing that makes me leery at this time, is the fan on temperature from the factory...220+ degrees is ludicrous! I plan on having that lowered to the 190° mark when I have the PCM modded...actually pulled over the other day because the temp was so high, had never seen it get there before. After some research I decided to try it again for the longer ride, and sure enough, car got to 220-225 degrees, then quickly dropped down to 210-212, then repeated several times...before I got home and shut her off. Doesn't seem to be operating poorly, just hotter than I had expected.
Thanks for all the help!
I ended up finding this article. Link
And using it, did some more troubleshooting on the transmission. Earlier in the week, the transmission was acting very strange, as if it was dragging the E-Brake when moving forward...reverse seemed to work ok, but the car had a lot of shuddering. I noticed the transmission fluid was low (even though I thought I topped it off when I replaced the filter/solenoids) so I topped it off, but the problems persisted.
Ended up following the testing procedures listed in the link above, and confirmed operation of the 1-2 Shift Solenoid, 2-3 Shift Solenoid, and 3-2 Shift Solenoid. I then swapped in my backup PCM again and fired it up. Transmission was shifting normally for the first time in a couple months, and engine was running beautifully. Took the car out for a test run, all was well...repeated later than night. And this morning I took the car for about a 30 minute drive...willing to say the problem is solved (although I still need to get the computer setup to remove the emissions codes and VATS). The only thing that makes me leery at this time, is the fan on temperature from the factory...220+ degrees is ludicrous! I plan on having that lowered to the 190° mark when I have the PCM modded...actually pulled over the other day because the temp was so high, had never seen it get there before. After some research I decided to try it again for the longer ride, and sure enough, car got to 220-225 degrees, then quickly dropped down to 210-212, then repeated several times...before I got home and shut her off. Doesn't seem to be operating poorly, just hotter than I had expected.
Thanks for all the help!
