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Pete
Pete, Mechanic
Category: Car
Satisfied Customers: 15838
Experience:  15 years automotive training and experience.
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Saab 9-5 Aero: Aisin Warner AW55-51SN in Saab 9-5, throws code

Customer Question

Aisin Warner AW55-51SN in Saab 9-5, throws code P0785 "shift/timing malfunction" which points to the SLS. replaced linear solenoids didn't cure, had valve body rebuilt and didn't cure. (VB rebuild included rebuild all solenoids and test at temp)

Symptoms: Shifts fine while car is cold, after about 30 minutes start to get rough downshifts esp 3-2 and 2-1. After P0785, clear and then very rough shifts N-D and N-R, as soon as car moves P0785 kicks again and transmission goes into limp mode.

Suggestions?
Submitted: 1 year ago.
Category: Car
Expert:  Pete replied 1 year ago.
My name is XXXXX XXXXX I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would ask to see if you still need help with this.
Customer: replied 1 year ago.

I posted the question yesterday and there have been no answers so I am still looking.


 


 

Expert:  Pete replied 1 year ago.
Were all solenoids replaced in the transmission including pressure control?

Was anything else on the transmission mechanically inspected or tested?
Customer: replied 1 year ago.

The first step was that all three linear solenoids (SLS, SLU, SLT) were replaced. That did not solve the problem.


 


The second step was a full valve body rebuild by a professional valve body rebuild company, all of the on/off solenoids were rebuilt. The VB was then tested including testing with hot AFT and everything was passed. For warranty purposes, they also rebuilt the original linear solenoids, which are what is on the VB right now. The rebuild included all of the Sonax upgrades.


 


When I re-installed the valve body I replaced the two rubber seals between the VB and the main transmission housing.


 


On the Saab 9-5 you can remove the valve body with the transmission in the car, so nothing else on the transmission was inspected.


 


The transmission fluid (AFT3309) is changed regularly, I usually do it every other oil change which would be between 10 and 15K. I use only the Mobil 3309 fluid.


 


Car has 145K on it

Expert:  Pete replied 1 year ago.
O.k.,from what you have described here as well as with what has been done already to try and correct this fault this sounds like there may possibly be mechanical damage or a mechanical fault in the transmission itself as I have seen some worn components in certain cases cause fault codes to set for other components in the transmission.This would have to be removed and inspected to see if there is a fault.

This can also sometimes be caused by wiring problems from the computer to the transmission or an internal computer fault itself causing the code and issue.

It is difficult to say for sure from here exactly what has caused this so it may be best to have a local transmission shop or dealer check into this problem to see if they can locate the fault and also repair it if needed.

I know this is not the answer you were looking for but I do hope this has helped in some way, thanks Pete.
Customer: replied 1 year ago.

Thanks, describes what is "left" in the system.


 


The issue is that the 03 is not worth a full transmission rebuild at this point. I love the car, but can't see sinking $3K+ into it if it's an internal transmission issue. Not only that, but finding Saab service these days is getting difficult. one of the two dealers in this area has already quit the Saab business.


 


Not sure what to do at this point.Do you happen to know if the Tech II has more information in it about what is happening?

Expert:  Pete replied 1 year ago.
The tech 2 is one of the best scan tools to read and delete codes as well as observe engine and transmission data and perform special functions but it may or may not help in isolating the fault here.

I hope this info has helped,if you need anything else let me know before rating my help here,thanks Pete.
Pete, Mechanic
Category: Car
Satisfied Customers: 15838
Experience: 15 years automotive training and experience.
Pete and 10 other Car Specialists are ready to help you
Customer: replied 1 year ago.

The car spent some time at the Dealer this past week, they reset the TCM and updated to the latest firmware with the Tech 2. Still throws P0785 when hot.


 


I have done a lot of reading in the WIS about this code, the description is that when the system determines that the SLS current is out of spec it throws this code. I can't see that being an internal issue on the transmission, can you? I also saw one posting on line of someone who had this issue and had the transmission replaced and was still getting it, I don't want to have that happen to me!


 


My next step is to replace the wiring harness between the transmission and the TCM or replace the TCM. Where would you start first?

Expert:  Pete replied 1 year ago.
Can you inspect the electrical connections at the transmission and computer to see if any fluid is inside them and let me know.

Thanks Pete.
Customer: replied 1 year ago.

I have done that. The connection to the solenoid is inside the valve body and is bathed in the transmission oil. That connection was removed and re-installed when I changed the SLS and when I changed the valve body


 


The transmission harness then connects to the main harness with two snap locked connectors under the battery. I took both of those off and inspected/cleaned the connections and did not find anything.


 


The TCM is in the passenger compartment behind the glove box. I took that off the other day and there was no corrosion or moisture.


 

Expert:  Pete replied 1 year ago.
O.k.,just wanted to make sure as some vehicles will have the transmission fluid work its way in the wiring all the way to the control unit and flood the control unit itself as I have seen before.

It is difficult to pinpoint this fault from here unfortunately.This does sound like it may be electrical and if the transmission side checks out o.k. and the wiring is good then this may be an internal fault in the transmission control unit itself.
Customer: replied 1 year ago.

Today I drove the car till it signaled the fault (about 30 minutes) then came home and disconnected the TCM from the car and let it sit outside of the car for about 10 minutes (it is cold, probably about 50 or so) The TCM was dead cold after that.


 


Then I put it back in the car. The engine was still operating at temp and I'm sure that the transmission fluid didn't lose a whole lot of temp either.


 


In about 2 minutes, the fault came back. Makes me believe that there are no heat related issues with the TCM. Do you concur?


 


That leaves either the transmission or the harness between the transmission and the main wiring bundle. Unfortunately that part from Saab is NLA. I'm searching for someone who has a transmission for sale that is willing to sell the harness separately.

Expert:  Pete replied 1 year ago.
I apologize for the delay.

This does sound correct with the TCM most likely not getting hot and causing this issue here and it may be an issue either with the wiring or the transmission itself.

It is difficult to say for sure from here.

Thanks Pete
Customer: replied 1 year ago.

I'm confused as to how something in the transmission (clutch, band, etc) would present as an electrical fault? The reason I ask is that I'd hate to go to all of the trouble and expense to get the transmission replaced and then find that it didn't solve the problem.


 


 


The specifics on the P0785 described in the Saab WIS says that this is a current too high, short to B+ or short to ground on the SLS.


 


I did find someone who will sell me a used transmission harness, I hopefully will get that installed next week some time after it arrives.


 

Expert:  Pete replied 1 year ago.
I apologize as above I had posted info on this possibly being the transmission itself causing this.I had this question confused with another and had to review the fault code completely again for this here.

This code will set for an electrical issue with the sls solenoid drawing to much current consumption.It does sound like this may be the transmission harness itself.Even though you did the hot/cold test the TCM is possible to have an intermittent internal electrical fault in some cases.

It is difficult to determine from here which of these would be at fault either possibly the harness or ther TCM.Usually if you do not see any wiring issues then this may be the TCM causing this here.
Customer: replied 1 year ago.

Pete


 


It appears that the harness did solve the problem. I've been driving the car for three days now and have put about 100 miles (highway and local, in traffic) on it and no gearbox fault indicator or codes. I'm cautiously optimistic that this is the issue.


 


Wanted to let you know since this may come up again with another question.


 


 

Expert:  Pete replied 1 year ago.
Thats great to hear.Let us know if you need anything else in the future.

Thanks Pete

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