98 blazer p0785 shift timing solenoid malfunction


mb66
10-17-2006, 02:13 PM
i'm getting this code (and only this code). i've searched the forum and found many threads about multiple transmission related codes caused by a faulty ignition switch. but i have just this code. if i clear it, it comes back within an hour of driving, and sometimes i notice "slugishness" like the transmission won't shift gears.

so i assume this is a valid code. doesn't anyone know exactly what causes this? is there an actual solenoid? and if so, where is it located. if this is internal to the tranny, i'm going to the shop.

thanks for any help.

BlazerLT
10-17-2006, 02:25 PM
i'm getting this code (and only this code). i've searched the forum and found many threads about multiple transmission related codes caused by a faulty ignition switch. but i have just this code. if i clear it, it comes back within an hour of driving, and sometimes i notice "slugishness" like the transmission won't shift gears.

so i assume this is a valid code. doesn't anyone know exactly what causes this? is there an actual solenoid? and if so, where is it located. if this is internal to the tranny, i'm going to the shop.

thanks for any help.

Yes, there is a solenoid they can replace by dropping the tranny pan.

Would be a good time to have the filter and fluid changed while you are at it.

brianneves
10-17-2006, 07:25 PM
i hate to say this but i just got done replacing the solenoids on a 97 s10 blazer with the same trouble code with no change in transmission performance. it is NOT the solenoids themselves. im still trying to figure it out, but here is some other helpful info. mine drives and shifts just fine until the transmission warms up. then it slowly finds itself stuck in third gear. thats why its sluggish, because your trans is not starting in first. its starting in 3rd.

if anyone has any suggestions for us with this code, please let us know!!!

thanks!!!!

BlazerLT
10-17-2006, 07:28 PM
i hate to say this but i just got done replacing the solenoids on a 97 s10 blazer with the same trouble code with no change in transmission performance. it is NOT the solenoids themselves. im still trying to figure it out, but here is some other helpful info. mine drives and shifts just fine until the transmission warms up. then it slowly finds itself stuck in third gear. thats why its sluggish, because your trans is not starting in first. its starting in 3rd.

if anyone has any suggestions for us with this code, please let us know!!!

thanks!!!!

Yours is the ignition switch in your steering column.

For any other year other than 1997 it will be the tranny most of the time.

The ignition switch in the steering column causes numerous things including the tranny problem.

The fix is in the how to section at the top of the forum.

http://www.automotiveforums.com/vbulletin/showthread.php?t=287636

As for this 1998, if it was earlier enough in the year and they were still using the same parts bin as the 1997 ir could be the solution.

brianneves
10-17-2006, 07:37 PM
hey thanks alot man. really appreciate the help. ive heard of the same thing happening, but i hate shooting a parts cannon at my truck not knowing for sure. thanks for the lead!!!!

BlazerLT
10-18-2006, 03:34 PM
no problem, with a 1997, the switch is the first thing to replace and is never a bad thing to do.

Travisthetiger
10-18-2006, 10:24 PM
I've had to replace/fix my ignition switch a few times. After the third time I figured out that a new switch was not needed, just an adjustment to line up the teeth. If you haven't purchased a new ignition switch, I suggest trying this to save money. When looking at the gear teeth on the old switch, rotate the gear so that there is a single tooth to the left, then a gap, then the rest of the teeth to the right. The gap between the teeth should be at a 90 degree angle to the switch (straight out). Turn the key to the AUX position and reinsert the switch. This should line everything up correctly and all you have to do is put everything back together. To get the key to rotate there is a push button under the steering column that can be pushed in. This should disengage the locking mechanism (sort of like those vehicles that you have to push the button to remove the key).

If you are having problems pulling the old switch out, there are two square holes on each side that you can insert a paper clip into (one at a time while pulling the switch out) and the switch should slide right out.

I haven't done this procedure in a while, so if I missed a step, or if it's still giving you problems, I'd be willing to take mine apart again and write everything down. I might even take pictures. LOL

BlazerLT
10-18-2006, 10:38 PM
I've had to replace/fix my ignition switch a few times. After the third time I figured out that a new switch was not needed, just an adjustment to line up the teeth. If you haven't purchased a new ignition switch, I suggest trying this to save money. When looking at the gear teeth on the old switch, rotate the gear so that there is a single tooth to the left, then a gap, then the rest of the teeth to the right. The gap between the teeth should be at a 90 degree angle to the switch (straight out). Turn the key to the AUX position and reinsert the switch. This should line everything up correctly and all you have to do is put everything back together. To get the key to rotate there is a push button under the steering column that can be pushed in. This should disengage the locking mechanism (sort of like those vehicles that you have to push the button to remove the key).

If you are having problems pulling the old switch out, there are two square holes on each side that you can insert a paper clip into (one at a time while pulling the switch out) and the switch should slide right out.

I haven't done this procedure in a while, so if I missed a step, or if it's still giving you problems, I'd be willing to take mine apart again and write everything down. I might even take pictures. LOL

We are not talking about the key tumbler, we are talking about the ignition switch which is a black electronic module in the steering column.

Travisthetiger
10-19-2006, 05:41 PM
We are not talking about the key tumbler, we are talking about the ignition switch which is a black electronic module in the steering column.

I am not talking about the key tumbler either. I've never removed the tumbler. I haven't had to fix it in a while, so maybe I didn't decribe it correctly. I would tear it apart and take a look, but the truck is currently in the shop for problems stated in the problems thread for GMC Jimmy.

This is the part I'm talking about. You can see the white teeth I was refering to on top of the "black electronic module" on the right. The picture shows the teeth in the correct position when the key is in AUX.

http://198.208.187.182/internet/PartImage.jsp?mfgname=ACDELCO&prodlinecd=1&acpartnbr=D1413D

brianneves
10-20-2006, 06:28 PM
i appreciate all the help with the tranny suggestions and the ignition switch info, but swapping the ignition switch did not help. i dont have the style of ignition switch shown in the link. i have the style that has the slot in it that cant be installed on the wrong gear tooth. thanks for the help, but do you have any other suggestions? a realtime tranny diagnostic shows that the 3-2 downshift solenoid goes to the condition of "short" after the engine has been ran for a while. it was suggested to me that this may be happening when the computer goes into closed loop and that it may not actually be a short in the 3-2 solenoid. what do you guys think?

BlazerLT
10-20-2006, 08:21 PM
i appreciate all the help with the tranny suggestions and the ignition switch info, but swapping the ignition switch did not help. i dont have the style of ignition switch shown in the link. i have the style that has the slot in it that cant be installed on the wrong gear tooth. thanks for the help, but do you have any other suggestions? a realtime tranny diagnostic shows that the 3-2 downshift solenoid goes to the condition of "short" after the engine has been ran for a while. it was suggested to me that this may be happening when the computer goes into closed loop and that it may not actually be a short in the 3-2 solenoid. what do you guys think?

reset your computer and have it relearn.

blazes9395
10-21-2006, 01:04 PM
i appreciate all the help with the tranny suggestions and the ignition switch info, but swapping the ignition switch did not help. i dont have the style of ignition switch shown in the link. i have the style that has the slot in it that cant be installed on the wrong gear tooth. thanks for the help, but do you have any other suggestions? a realtime tranny diagnostic shows that the 3-2 downshift solenoid goes to the condition of "short" after the engine has been ran for a while. it was suggested to me that this may be happening when the computer goes into closed loop and that it may not actually be a short in the 3-2 solenoid. what do you guys think?

I know this thread has been hijacked, but I think the original thread starter found his problem. As with one, this could be a tricky one. Does it do it only when warm? If this is the case, when cold, does it shift properly, without any long shift patterns? You mentioned you changed the solonoids, and have a real time scanner, if its bidirectional, can you actually command a shift manually? This is where you have to see whats going on up to this point. If you can manually command a shift via scanner, I would still be looking at electrical, if not, then you could have a hanging piston in the valve body when warm, as usualy a result of wear and heat causing expansion, in which case the valve body has to be pulled.

When was the last time you serviced the tranny, does it recieve regular servicing, have you noticed anything else funny, oil leaking, how is the oil level, colour condition etc.

brianneves
10-21-2006, 02:09 PM
hey, thanks again for all the info. i at this point am leaning toward the valve body, the computer, or the 3-2 kickdown solenoid (that has not yet been replaced). the transmission works flawlessly until the truck gets to operating temp. then it gets stuck in 3rd. it will manually shift to second by using the sift selector but no other gears. unfortunately i do not have 2 way with my scanner. i cant command the solenoids. what i do know from the scanner is that the shift solenoids are working properly until the engine warms up. then they both go into the "off" position leaving the transmission stuck in third. what i also noticed was that the 3-2 downshift solenoid goes to the "on" position when the symptoms show. when i did the test drive with the scanner the downshift solenoid actually kicked on when i was at a stop light and remained on for the duration. if you shut the truck down for about one minute, it will shift through the gears properly again, but only once. then it immediately becomes symptomatic again. this leads me to think that it is heat related, but not heat related to the transmission or its fluid because one minute is not long enough at all for the fluid to cool any. the scanner shows no shorts or opens in the shift solenoids but shows a short in the downshift solenoid ONLY after the transmission warms up and becomes symptomatic. im going to change the downshift solenoid and i will update. once again any info or suggestions is greatly appreciated

the transmission was rebuilt by AAMCO transmissions 12500 miles ago. 500 miles past its warranty.........

nrecob
09-19-2008, 01:42 AM
hey, thanks again for all the info. i at this point am leaning toward the valve body, the computer, or the 3-2 kickdown solenoid (that has not yet been replaced). the transmission works flawlessly until the truck gets to operating temp. then it gets stuck in 3rd. it will manually shift to second by using the sift selector but no other gears. unfortunately i do not have 2 way with my scanner. i cant command the solenoids. what i do know from the scanner is that the shift solenoids are working properly until the engine warms up. then they both go into the "off" position leaving the transmission stuck in third. what i also noticed was that the 3-2 downshift solenoid goes to the "on" position when the symptoms show. when i did the test drive with the scanner the downshift solenoid actually kicked on when i was at a stop light and remained on for the duration. if you shut the truck down for about one minute, it will shift through the gears properly again, but only once. then it immediately becomes symptomatic again. this leads me to think that it is heat related, but not heat related to the transmission or its fluid because one minute is not long enough at all for the fluid to cool any. the scanner shows no shorts or opens in the shift solenoids but shows a short in the downshift solenoid ONLY after the transmission warms up and becomes symptomatic. im going to change the downshift solenoid and i will update. once again any info or suggestions is greatly appreciated

the transmission was rebuilt by AAMCO transmissions 12500 miles ago. 500 miles past its warranty.........

brianneves, did changing the 3-2 shift solenoid do the job? (I sure hope so because I have the EXACT same issues with my '97 Blazer) and I've already changed the other shift solenoids and replaced the AC Delco ignition switch wiring (what an expensive PITA that made NO DIFFERENCE :headshake )

mb66
10-27-2008, 11:09 AM
f.y.i., i am the original poster of this thread from two years ago. i did take
it to the shop and they replaced the 3-2 solenoid - which didn't fix the problem.

they did a lot of further diagnosis and called some experts somewhere and
concluded it was the main vehicle computer which was erroneously sending
a solenoid control signal.

after they figured it all out, they said everything made sense (the way it
happened just once - you clear the code and reset the computer and it
won't get stuck again until the vehicle sits overnight and cools down again).

i drove around with a OBD scanner in the car and reset the code everytime
it got stuck (once a day) until i sold the vehicle. so i don't know for certain
that replacing the computer would actually fix the problem. but the shop
was confident after several days of diagnostics.

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