The linear solenoids on the Aisin valve bodies control line pressure, shift pressure, shift/engagement feel and lockup control. A linear solenoid that is sticking can cause all sorts of problems depending on the solenoid and the transmission type. The linear solenoids need to be rebuilt as much as the valve bodies do on these transmissions. The pintles stick and the outer shell (can or shell) can become distorted or loose.
A 2001 Volvo S60 come into or shop with a smoked AW 55-50 transmission that needed to be replaced.
The AW 55-50 transmission has a feature that Volvo calls “Neutral Control.” What is “Neutral Control” and what is its function? To tell you the truth, I wasn’t really sure, but below is what I was able to both find and figure out about it.
The 604 was the first American computer-controlled transmission with adaptive shift strategy. The relearn process was not much different from what it is for today’s transmissions. For those of you who were not in the transmission industry back then, there was no quick-learn procedure for the 604. The quick-learn feature was not available until the mid-’90s. You actually had to drive the car at different throttle openings to relearn the shift adapts, and it could take 30 minutes or more of driving time to get it right.
One of our customers rebuilt an AW55-50 and had repeat complaints of a 2-3 shift flare. Everything on the transmission side of this complaint was corrected and rechecked. Everything on the valve-body and control side of the complaint was done, checked, verified and looked at again. Resets/relearns – you name it, they tried it. Eventually another valve body was tried, but the car continued to have the 2-3 flare.
I recently received a phone call from a shop that was working on a 2001 Volvo with an AW 55-50 transmission. The vehicle would not move when shifted from Park to Reverse. If the selector was first put into Drive then moved to Reverse, engagement was normal. The manual linkage was checked, confirming that the manual valve was in the reverse position.
Last month we explained the variety of operating modes the different manufacturers use to control AW55-50 units in their vehicles. Knowing the modes and when they are activated is the first step in making an accurate diagnosis. A symptom reported by a customer may be normal, intended operation for one brand of vehicle and a legitimate problem in another. As part of your diagnosis, you also should be aware that every manufacturer has at least one transmission-control-module (TCM) reflash or replacement bulletin to address various transmission concerns.
As you can see, there are a lot of these transmissions on the street. It is important that you understand what a normal operating condition is and what is not normal for the vehicle that you are working on. Not all AW55-50 transmissions have the same operating features.