Trans. Code P0785 (Slipping in 1st)

I noticed my trans. seems fine when I first start the truck, after a few minutes it starts to slip when I start out from a stop, I start out real slow then it seems fine when in 2nd or 3rd. Had Autozone pull the codes and the only one that came up is P0785 (Shift Timing Solenoid Malfunction) a $29.99 part there. I have read other posts about a ignition switch causing the problem, but I don't have any other codes or any dash problems. What are the chances it is the On/Off Shift solenoid (which is on the Autozone part printout) and not the ignition switch. Is the Shift solenoid mounted externally and where? I would greatly appreciate any help.

I noticed my trans. seems fine when I first start the truck, after a few minutes it starts to slip when I start out from a stop, I start out real slow then it seems fine when in 2nd or 3rd. Had Autozone pull the codes and the only one that came up is P0785 (Shift Timing Solenoid Malfunction) a $29.99 part there. I have read other posts about a ignition switch causing the problem, but I don't have any other codes or any dash problems. What are the chances it is the On/Off Shift solenoid (which is on the Autozone part printout) and not the ignition switch. Is the Shift solenoid mounted externally and where? I would greatly appreciate any help.

Probably not an ignition switch problem. Do not forget to factor in 4-5 qts of tranny fluid and a gasket and a filter (optional but a good idea) in addition to your $29.99 part. Messy job.

Have you ever changed your filter at all since 1999?

The trans was flushed about 1 year ago, it's still bright red and dosn't smell burnt. I was going to replace the shift solenoid, but I cannot find anything on the web about where this thing is located. It all started today, but I haven't even got under the truck to look yet, but any info will be very helpful.

I would say that the code that you got warrants replacing the part (P0785 (Shift Timing Solenoid Malfunction) - "malfunction" being the key word. Its a cheap enough part. I'm assuming the tranny filter was changed when it was flushed a year ago.

A Haynes or Chilton manual should tell you where the solenoid is and how to replace it.







The trans was flushed about 1 year ago, it's still bright red and dosn't smell burnt. I was going to replace the shift solenoid, but I cannot find anything on the web about where this thing is located. It all started today, but I haven't even got under the truck to look yet, but any info will be very helpful.

Has anyone replaced a shift solenoid, and where is it located? I have read about different shift solenoids (1-2, 3-4) Is there just 1, or are there different shift solenoids? My code only stated "Shift Timing Solenoid Malfunction" P0785. I ordered the part from Autozone which is listed as a "On/Off Shift Solenoid" along with a gasket, filter and 5 qts. Trans. fluid. I'm ready to do the job but just need some help. Autozone only had 3 parts avail.(Pressure Control Solenoid, On/Off Shift Timing Solenoid, Torque Converter Clutch Lock-up Solenoid.) I hope I ordered the right one. Please Help!

What kind of truck or transmission do you have? I have an ATSG manual for the 4L60-E. It says there is a 1-2 shift solenoid and a 2-3 shift solenoid (aka A and B solenoids) which are identical and work together in four combinations to shift the transmission into different gears. These solenoids look like small boxes. The book says they will bring in diagnostic trouble codes 081 and 082. There is also a round solenoid called the 3-2 control solenoid that says will bring in code 066 when it breaks. It says it is supposed to improve the 3-2 downshift.

I am not sure how to convert the tranny codes to the code you have P0785. I am not a transmission expert - but I did replace my valve body last Sunday (including all the solenoids) and I have an ATSG manual (and the truck actually still works!).

I have a 99 Blazer LS, 4.3L V6 with a 4L60E trans.

The shift solenoids look like little boxes and are held in to the valve body with small clips (one each). Be very careful not to break the electrical connectors. From looking at the book, it looks like once you remove the clip, you will be able to pull the solenoid horizontally out of the valve body and then slip your new one in.

I am not sure which one of the two you would replace. I am not even sure if I am talking about the correct solenoids. I guess that you are getting what you pay for here with me.

Does the valve body need to be removed?

Thanks for all your help.

No, I do not think so. I am pretty sure the clip is accessible from the bottom.

Well I removed the trans. pan and noticed the solenoids are accessable from underneath by just removing the pan, just pull down on the retaining clip (Looks like a wire e-clip) and the solenoids easily slide out of the side of the valve body ( Very simple), but the 1 solenoid I needed to remove (3-2 On/Off Shift Solenoid) had the clip put on from the upper side of the valve body so I had to remove the valve body and bring it in the work shop just to remove a simple clip that was put on from the wrong end when it was rebuilt 90,000 miles ago. I would suggest anyone going through all this should make sure all clips are put on from the bottom of the valve body for easy replacement in the future. Let's see if the solenoids do the trick, because the local trans. shop said it needed to be rebuilt at $1600.00.

keep us posted.

I will need to do this soon myself.

Well, I replaced the valve body gaskets, all 4 solenoids on the valve body and a fresh filter and new fluid. Still the same problem with 1 st gear on initial take off then it starts in 2nd from then on, but the funny thing is if I shut off the truck for 10 seconds then restart I have first gear for the initial take off again then it starts in 2nd again. It does this everytime I shut it off for 10 seconds. I cleared the ses light after all the work was done, when I started the truck for the first time it came back on within 20 seconds and has not went out. I haven't check the code to see it it was the same as the initial one yet.

Sounds like my issue(s), I've been searching all over the Blazer thread looking for someone with the same symptoms. I have a '97 auto 4wd. The trans feels like it start out in 2nd gear, but I can shift it manually which gets me 1-3 but no OD. I found a post that indicated it could the ignition switch, but that incorrectly installed aftermarket remote starters could also cause the problem. I yanked out the remote started which corrected the problem temporarily. I think (I need to retest) overdrive cause the issue to resurface. I normally drive in "3" in the city and only use OD for the highway. I drove for 1/2 hr to an hour in 3rd, and as soon as pushed in into OD the CE light came back on. I haven't had a chance to get the codes out yet ( idebating between buying a scanner and taking it to the garage). I'll post any progress I make, but would appreciate anyone elses thoughts.

Thanks

Take it to Autozone for a free code read.

Well, I replaced the ignition switch too. Still the same problem. I took it to Cottman to see what their diagnosis is.

Was the tranny filter replaced at all?

Filter changed little over 10,000 miles ago. Just seems electronic to me in that when I "reset" the computer by unhooking the battery that it temporarily corrected the problem. I'm 99% sure it resurfaced at the exact time I shifted it to OD. I'm going to retest the OD timing tonight. I'll keep you posted.

JCP - Any news from Cottman?

Filter changed little over 10,000 miles ago. Just seems electronic to me in that when I "reset" the computer by unhooking the battery that it temporarily corrected the problem. I'm 99% sure it resurfaced at the exact time I shifted it to OD. I'm going to retest the OD timing tonight. I'll keep you posted.

JCP - Any news from Cottman?

Since you had a shift solenoid fault code in your computer and you've replaced all the solenoids (whew!$) and this issue still occurs, I wonder if there might be a wiring issue, like a partial short to ground. The 1-2 shift solenoid is energized in 1st, overdrive, neutral, and reverse though, so if there was a fault in that circuit, it would seem like all those ranges would be affected.

Good luck.

JCP did all of the selonoid changes - I haven't dug into the codes yet (hoping to Autozone this weekend for a read). The wiring is an interesting thought though. I had a squirrel problem about a year ago. Darn thing chewed threw my main harness and I had to resplice 5 or 6 wires. GM doesn't give you much "extra" wire in the event of a squirrel attack.

Scrap that thought - it's not limited to just overdrive. I unhooked the battery and it worked through all 4 gears just fine.

I can give you my thoughts on the scanner....I also have a 97 4.3L auto with 4x4 and the CE light comes on about weekly. The scanner paid for itself for me. I am just about to the point now where I keep the thing in the glove box!

Scrap that thought - it's not limited to just overdrive. I unhooked the battery and it worked through all 4 gears just fine.

You should go and have it hooked to a Tech2 and have the computer relearn monitored.

Your main pressure solenoid could be faulty.

Cottman says I need a rebuild, So I am having it done for $1500. They claim the fluid is leaking past the valve in the valve body and some of the internal componets are pretty worn (Springs and bearings). So this includes the updated valve body and everything else.

Cottman says I need a rebuild, So I am having it done for $1500. They claim the fluid is leaking past the valve in the valve body and some of the internal componets are pretty worn (Springs and bearings). So this includes the updated valve body and everything else.

You mean the main pressure solenoid?

Cottman says I need a rebuild, So I am having it done for $1500. They claim the fluid is leaking past the valve in the valve body and some of the internal componets are pretty worn (Springs and bearings). So this includes the updated valve body and everything else.

Obviously Cottman knows more about transmissions than I do, but I just bought a new valve body with all new solenoids and valves and springs and spacer plate for just over $200. And you know what is involved with replacing the valve body as far as labor.

To many trannies being replaced for no good reason.

They don't even really know what is REALLY wrong, just a theory and a $1500-2000 pricetag.

I was reading the thread Blazee posted on common trans issues
http://www.automotiveforums.com/vbulletin/showthread.php?t=461182

Reading through the tech bulletin, I decided to check the voltage at the #24 fuse with the CEL out which read 12.87. Drove it to the end of the driveway - CEL illuminated and I lost 1st and 2nd. Checked the voltage again - it read about 3.5 w/ the truck not running. Started the truck - it was back to 12.87, and 1st and 2nd came back (CEL is still illuminated). These electronic tranny are a pain in the a$$. The 700R4's may have been crap, but atleast when they started acting up, you knew it was time for a rebuild!!

After a month I finally got my truck back. Cottman rebuilt the trans., then told me it is still doing the same thing. Then they replaced the computer under the hood and that fixed the problem, $1775.00 later. but now my key gets stuck sometimes when I turn off the truck, the Neutral or Drive dosent highlight with the gear shifter but all other gears do, and sometimes when the key is removed the gear selector stays lit until you restart the truck, move the gear selector and turn it off again. Could this be the new ign. switch I installed or could this be from the linkage from the gear selector to the trans.

So they misdiagnosed the problem and then charged to actually fix it, I'd be in small claims court with them. A thorough scan with a trans capable scanner would have probably avoided most of what went on here! Commands could have been given to the shift and pwm solenoids to confirm operation and slippage percents looked at.

I was reading the thread Blazee posted on common trans issues
http://www.automotiveforums.com/vbulletin/showthread.php?t=461182

Reading through the tech bulletin, I decided to check the voltage at the #24 fuse with the CEL out which read 12.87. Drove it to the end of the driveway - CEL illuminated and I lost 1st and 2nd. Checked the voltage again - it read about 3.5 w/ the truck not running. Started the truck - it was back to 12.87, and 1st and 2nd came back (CEL is still illuminated). These electronic tranny are a pain in the a$$. The 700R4's may have been crap, but atleast when they started acting up, you knew it was time for a rebuild!!


Finally got off by A$$ and went to autozone for the code scan. The pulled out a P0740, P0750, P0753, P1740, and a P1860. Most of which are on the tech bulletin pointing me toward the ignition switch. I'm at my wits-end. The problems are so sporadic. I drove it the whole way to autozone and back (approx 40 miles) with no problems other than the CEL staying on.

Thought I'd let everyone know that my tranny fell victim to the ole ignition switch. Replaced it last week, and put about 200 miles on this weekend. NO CEL!!!!! It really wasn't as bad to replace as I thought. Autozone tried to tell me I needed a new computer, and they never heard of the ignition switch problem. Guess it pays to do a little research, before you go swappin out parts. Well I guess atleast they good for reading the codes for free.

I'm also trying the acetone additive thing to see what happens.

Thanks everyone for your thoughts and insights.

Thought I'd let everyone know that my tranny fell victim to the ole ignition switch. Replaced it last week, and put about 200 miles on this weekend. NO CEL!!!!! It really wasn't as bad to replace as I thought. Autozone tried to tell me I needed a new computer, and they never heard of the ignition switch problem. Guess it pays to do a little research, before you go swappin out parts. Well I guess atleast they good for reading the codes for free.

I'm also trying the acetone additive thing to see what happens.

Thanks everyone for your thoughts and insights.

Glad your back on the road again and thanks for coming back to the board and letting all of us in on the fix, I never trust the monkees at the parts stores, In the old day's,(30 years ago) lots of auto parts guy's were former mechanic's, now it's a complete different story.
Happy Motoring awc109

I noticed my trans. seems fine when I first start the truck, after a few minutes it starts to slip when I start out from a stop, I start out real slow then it seems fine when in 2nd or 3rd. Had Autozone pull the codes and the only one that came up is P0785 (Shift Timing Solenoid Malfunction) a $29.99 part there. I have read other posts about a ignition switch causing the problem, but I don't have any other codes or any dash problems. What are the chances it is the On/Off Shift solenoid (which is on the Autozone part printout) and not the ignition switch. Is the Shift solenoid mounted externally and where? I would greatly appreciate any help.

My transmission is doing the exact same thing after the rebuild. I have swapped all solenoids and the valve body, with no fix! Was the ignition switch ever suspected or did cottman know it was the pcm.:banghead: