Hi All,
You can add my car to the list having these kinds of problems. I imported the car into NZ at 45k and noticed an intermittent issue with the AT shortly after which would occur about every six months or so. It would generally occur when the following sequence of events had happened:
1) The vehicle was brought up to operating temperatures and run for an extended period of time at motorway speeds.
2) The vehicle was then stopped and turned off for at least 20 minutes or longer and allowed to partially cool.
3) It was then taken for another run at a minimum of 100Kp/h. If it was carrying a bit of load, that also exacerbated it.
4) More likely to happen in the summer months.
Currently the car has about 145K on it and I have had one solenoid kit go (definitely a faulty shift solenoid "A"). The symptoms of that were quite different in that every time you got to over 105Kp/h for more than about 5 minutes, you were guaranteed to see the AT light come on. As you guys have worked out, this is a separate issue.
To date the work I have had done is as follows:
1) Take the car into an auto-trans shop with the light on. Using their diagnostic computer, it spits out a fault code for Shift Solenoid "A".
2) The auto-trans shop retested the fresh solenoid pack and confirmed that this was operating normally. They then sent me to an auto-electrician
3) The auto electrician tested the wiring loom inside the auto trans (OK), retested the solenoids (OK).
4) I was able to locate a full workshop manual for the R34 on the internet and supply this to the auto-electrician. This contained a wiring diagram for the tiptronic auto-trans used in the R34. Through this they were able to work out that the only other component in the same circuit 'Shift Solenoid "A"' is a "Shift Solenoid A Pressure Detection Switch" (PN 31041-4AX01 I believe), which they figure must be the cause of the problem. It is interesting to note that there are two pressure switches in the auto-trans, but only one will generate a unique fault code clearly stating that it is a auto trans pressure switch issue. The second one, and the one that I believe we are all having problems with, trips the fault code for the Shift Solenoid A, fires up the AT light on the dash, and puts the car into "Limp Home Mode". This obviously makes diagnosing the issue a bit harder, especially when this type of code is not stored when the vehicle is turned off.
So, right now I have a new pressure switch in my glove box waiting for me to get annoyed enough with the car want to put it in. The switch cost me NZ$150 ex Japan, and the auto-electrician tells me that it is buried inside the trans somewhere, and they will need the help of a transmission specialist to get to it.
I have attached the wiring diagram and circled the component I think is the source of our problems.
Your thoughts?
InspectorGadget
R34_Wiring_Diagram.pdf