4l60e&P0785
Thread Starter
Launching!
Joined: Jun 2009
Posts: 213
Likes: 3
From: Manitowoc wi.
4l60e&P0785 Hey guys, been a while since i posted and would like to share a little problem that I had recently with my ls swap/4l60e transplant in my 66 chevelle. Last weekend,my wife and I attended the route 66 super chevy show i Joliet Il. This trip is roughly 220 miles one way and all went smooth until the last stoplight in town near our hotel. Upon accelerating from the light I noticed that the trans was stuck in third gear,(No 1st 2nd or OD). Damm. Scanned for codes and got the dreaded P0785. Nurse the car back home 220 miles in third gear default mode which I might add was not fun with 60 mph being the top speed i was able to achieve with the 3.73 gear ratio. Pulled the pan and threw a 3/2 solenoid at it with no luck. Easy to do and figured I needed a fluid change anyway.Well now the fun starts. Decided to check the power supply to the solenoid when I had it apart to change the solenoid and had B+ voltage on the red wire. OhOh, never checked the other wire(control side) to pin 79 of pcm. Pulled PCM blue connector from pcm and checked resistance and found that wire was showing a constant grounded condition. I then removed the trans main connector from the case and the ohmeter no longer showed no continuity to ground. It appears to be shorted to ground inside of the case within the internal wiring harness.Have any of you guys with alot of experience seen this before? Have not had time to pull it apart to inspect the harness yet, but I suspect the the control side wire for the 3/2 solenoid to be rubbed through some where within the case. I will keep you all posted as to what I find.
Thread Starter
Launching!
Joined: Jun 2009
Posts: 213
Likes: 3
From: Manitowoc wi.
Ok guys I am back to report my findings.I previously reported that I had continuity to ground on pcm pin 79. I had my meter on audible alert and falsely assumed I had a dead short inside the internal wire harness in the case. With a little more testing I found that I was reading 3.7 ohms of resistance to ground on the power feed to the trans. This is with the 3/2 solenoid disconnected. Checked all the other solenoids and found the same.After many hours of electrical testing I found that the resistance was coming from the O2 sensor heater circuit which is connected to a bussed ignition activated power source. Now, this system had been operating perfectly flawless before, so why problems now? GM wired the early O2 sensor heaters to be key switched hot and grounded constantly. so I know that this should not be a problem as I followed their cue and wired mine this way. So I ignored the wiring issue and put everything back together.With the trans pan still off I decide to manually try to activate the 3/2 solenoid by grounding pin 79 of pcm connector with the key on and lo and behold the solenoid came to life.What i suspect was that the p0785 code was no longer stored in the memory as I had the power feed disconnected for a great deal of time. If I had cleared the codes after making the initial repair,I could have avoided the wild goose chase all together. After the test drive everything is back to normal. Bad case of dumb a##.
Teching In
Joined: Oct 2019
Posts: 20
Likes: 3
From: NC
I am dealing with a p0753 that wont go away after changing solenoid. I left the battery unhooked for a while and the light came back on, same code. Had it read with a better tool by a better guy and the light has now gone away but trans has not fixed itself yet (only gives me 2nd and 3rd)
Had the motor swapped today so maybe the extended period of now power will help me. Hope my issue is as simple as yours
Had the motor swapped today so maybe the extended period of now power will help me. Hope my issue is as simple as yours
TECH Junkie
Joined: Jun 2008
Posts: 3,202
Likes: 1,390
From: Nitro Alley
I am dealing with a p0753 that wont go away after changing solenoid. I left the battery unhooked for a while and the light came back on, same code. Had it read with a better tool by a better guy and the light has now gone away but trans has not fixed itself yet (only gives me 2nd and 3rd)
Had the motor swapped today so maybe the extended period of now power will help me. Hope my issue is as simple as yours
Had the motor swapped today so maybe the extended period of now power will help me. Hope my issue is as simple as yours
Even google searches bring up a bunch of results from our website...
I just was responding to another members post on this DTC within the last month...
I guess you didn't even look through the very first page of threads???
Why did you hijack a thread that is about DTC P0785?
I am going to go back one page and scroll down 26 threads... copy my questions from that thread and paste them here; since you seem incapable...
First... Which transmission are you discussing? ...4L60E Family? ...4L80E Family? What vehicle is this in?
Next are you stating:
A. That you had this DTC set; you replaced the 1-2 shift solenoid and the DTC is still set?
-OR-
B. That you replaced the 1-2 shift solenoid for some other reason and since then, the DTC is set?
Otherwise...
Do you have this DTC set current or in history?
Do you have any other DTCs set current or in history?
Do you have any drivability issues or concerns?
Do you have a proper 1-2 shift?
Do you have a proper 3-4 shift?
Have you serviced the transmission or replaced any parts recently?
Normally, when this DTC sets; I look at the solenoid and it's connection, the internal wiring harness and it's connection, the external wiring harness and it's connection, and lastly if need be the PCM and it's connections.
Next are you stating:
A. That you had this DTC set; you replaced the 1-2 shift solenoid and the DTC is still set?
-OR-
B. That you replaced the 1-2 shift solenoid for some other reason and since then, the DTC is set?
Otherwise...
Do you have this DTC set current or in history?
Do you have any other DTCs set current or in history?
Do you have any drivability issues or concerns?
Do you have a proper 1-2 shift?
Do you have a proper 3-4 shift?
Have you serviced the transmission or replaced any parts recently?
Normally, when this DTC sets; I look at the solenoid and it's connection, the internal wiring harness and it's connection, the external wiring harness and it's connection, and lastly if need be the PCM and it's connections.
Teching In
Joined: Oct 2019
Posts: 20
Likes: 3
From: NC
I just joined the site and barely know how to use it. Yes i have done all kinds of searching, i even saw the same thread you quoted. No i didnt hijack this thread because for one, he solved his problem. I was simply sharing my story and ending it by saying "i hope my problem is as simple as yours" because his solution made me laugh after a bad day. I didnt ask him for any help. So i didnt hijack anything. Get over yourself man if u want to help or give advice thats not how you are gonna speak with me, or u can not help me at all i dont care because i didnt ask you either. U assume i want help and havent searched because of my post but read again mr know it all.. not once in my post did i say i was here on that mans post looking for any help or advice
On The Tree
Joined: Sep 2018
Posts: 161
Likes: 4
From: New Zealand
I just joined the site and barely know how to use it. Yes i have done all kinds of searching, i even saw the same thread you quoted. No i didnt hijack this thread because for one, he solved his problem. I was simply sharing my story and ending it by saying "i hope my problem is as simple as yours" because his solution made me laugh after a bad day. I didnt ask him for any help. So i didnt hijack anything. Get over yourself man if u want to help or give advice thats not how you are gonna speak with me, or u can not help me at all i dont care because i didnt ask you either. U assume i want help and havent searched because of my post but read again mr know it all.. not once in my post did i say i was here on that mans post looking for any help or advice
If it does, then it must be leaking where it seals or something.
Trending Topics
Registered User
Joined: Nov 2020
Posts: 1
Likes: 0
Ok guys I am back to report my findings.I previously reported that I had continuity to ground on pcm pin 79. I had my meter on audible alert and falsely assumed I had a dead short inside the internal wire harness in the case. With a little more testing I found that I was reading 3.7 ohms of resistance to ground on the power feed to the trans. This is with the 3/2 solenoid disconnected. Checked all the other solenoids and found the same.After many hours of electrical testing I found that the resistance was coming from the O2 sensor heater circuit which is connected to a bussed ignition activated power source. Now, this system had been operating perfectly flawless before, so why problems now? GM wired the early O2 sensor heaters to be key switched hot and grounded constantly. so I know that this should not be a problem as I followed their cue and wired mine this way. So I ignored the wiring issue and put everything back together.With the trans pan still off I decide to manually try to activate the 3/2 solenoid by grounding pin 79 of pcm connector with the key on and lo and behold the solenoid came to life.What i suspect was that the p0785 code was no longer stored in the memory as I had the power feed disconnected for a great deal of time. If I had cleared the codes after making the initial repair,I could have avoided the wild goose chase all together. After the test drive everything is back to normal. Bad case of dumb a##.
I joined this forum because I just did an LM7 swap into a 98 Tahoe, using the 98 4l60e. I only have 3 codes...
p0785 - how I found this thread
p0134 - O2 sensor 1 heater
p0154 - O2 sensor 2 heater
I had no idea the two issues could be connected. Can you describe in a little more detail what you had to change in the wiring? I'm using a new aftermarket harness so something inside might not be wired correctly.
Thanks!
-Beau
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