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The Transmission Shop, Transmissions - Automobile, Garland, TX
Rebuild Or Not
One of the most problematic transmissions on the road today is AW55-50SN Transmission. This transmission can be fitted to different vehicles from different manufactures including General Motors, Volvo, Saturn, Nissan, Saab, Opel and Renault. These are not interchangeable as they have different operational differences.
The AW55-50SN is a 5 Speed electronically controlled Transmission. The TCM (transmission control module) sends signals to the Solenoids to achieve the best possible ratio. The TCM also controls the line pressure as well as the Apply and release pressure for the Torque Converter Clutch, by commanding this, the vehicle can obtain the maximum fuel efficiency.

At “The “Transmission Shop, our modern diagnostic equipment and certified technicians take pride in our ability to diagnose and repair these transmissions, in some cases saving you as much as 70% of a major overhaul.
The Component known as the “Valve Body” has been a major issue in these transmissions, and by knowing these and what corrective procedures need to done we have saved our customers not only time but a fair amount of monetary expenses.
In this article we will touch on some of electronic sensors,Valves and what they do.
One of the issues we have seen is that some owners with vehicles that have this type of transmission think that by adding fluid, this will correct their problem or condition. The main problem with this is not knowing how to check and fill this transmission. This transmission has a 22mm ‘Plug” which looks as like it may be where to fill it, but this “plug” is actually a band anchor. Loosing this plug will release the band causing a no 3rd condition, and in some vehicles, it may require removing the transmission to reapply the band correctly.  Removing the turbine sensor and using this opening to top off the fluid will eliminate the possibility of disengaging the band.
Having low or high fluid can create erratic pressure or poor linear solenoid control that can cause TCM (transmission control module) to produce high pressure. The Linear Solenoids (SLT, SLS and SLU) read this high pressure reading and react accordingly as they work at variable states dependent on gear and load that’s required from the transmission.
The linear Solenoids determine the engagement by adjusting hydraulic pressure.
The shift Solenoids (S1, S2, S3, S4, and S5) determine the basic parameters for different shift points, by accelerator pedal and vehicle speed. The quality of the shift is decided by control of the torque through the transmission.
This transmission allows for two shifting patterns, your Normal driving and Winter Mode.
In your normal mode, shifting and Lock-up occur at lower speeds to increase fuel efficiency or reduce fuel consumption. Under rapid acceleration, the TCM detects this and changes to what is called a third mode, or Sport mode.
Now, back to our Linear Solenoids, The first one will be the SLT Solenoid, this is the line pressure solenoid and is normally open 3 port type.
The TCM controls this transmission using 300 Hz, commanding current from 0.0 to1.1 amps. The TCM uses this current to measure the amount of pressure. Under an electronic failure, the solenoid is designed to go into maximum line pressure.
The SLS is a shift pressure solenoid. Like the SLT, it is a 3 port type and runs at the same frequency and currents. This Solenoid is to “Buffer” the shift and is adjusted depending on load or even driving conditions.
The SLU Solenoid is the Torque Converter lock-up pressure control solenoid, this solenoid however is normally “closed” not 3 port type.
Any of the above solenoids that fail can cause multiple symptoms on your transmission.
The TFT (transmission fluid sensor) sensor is a thermister and part of the internal wiring harness assembly. The sensor has 5 volts feed and because of different temperatures in the fluid it sends a signal back to the TCM which then calculates temperature and modifies shift quality and TCC (torque converter Clutch) operation.
The Output Shaft Speed Sensor is actually a Hall Effect sensor. This sensor calculates vehicle road speed. It is mounted in the case by the park gear and front differential transfer gear assembly. The sensor needs 0.6 volts to activate it. As your vehicle moves, the toothed gear passes by the sensor and emits a frequency or square wave. The TCM then uses this signal to determine vehicle road speed.
The Input Shaft sensor, like our output sensor is basically the same, however this sensor “reads” from the teeth on the forward/direct clutch housing. The “output” from this sensor determines the shift patterns, line pressure and gear ratios. It also determines torque converter clutch slippage.
Both, the output and input sensors should have a reading of > than 10M Ohms at 68 F (20C.)
The Pressure Relief valve and spring prevent line pressure from exceeding 360PSI.  Higher pressure moves the valve against the spring opening and exhaust. Having a broken spring or a “stuck” valve can cause high or low line pressure.
Solenoid modulator Valve, the SLT, SLS and SLU solenoids we discussed earlier are only able to work within a set pressure, any pressure that exceeds that will overload the valve and can cause damage. The Modulator Valve spring produces the force that regulates the pressure so that it equals line pressure.
The Forward Clutch Valve. This Valve responds to your throttle signal, and depending on the gear selected, this valve regulates drive fluid at the forward clutch oil circuit that applies the pressure to the forward clutch.
Having this valve “stuck” will give you a harsh or very firm engagement from neutral to drive.
The Neutral Relay Valve, works on the valve spring force and controls the route of fluid into the forward clutch circuit. Having a “stuck” neutral  relay valve will cause a no drive or slip condition.
Torque Converter Clutch Valve and spring is to prevent the cooler fluid from revering direction.
Cooler by-pass Valve, prevent the cooler and Lube pressure from exceeding 3- PSI.
Having a stuck Cooler Valve or broken spring will cause cooler or lube pressure to be too high.
The Components discussed above are only a few as we did not get into the internal moving parts or hard parts of the transmission.
Knowing how these transmissions work, and proper diagnosis allows us to offer repairs that you would normally not expect to hear from most shops.
With the Valve Body having all these solenoids and valves, the chances are that the problem originated from this componenet,or is causing the problem. Our equipment is state of the art, and our certified technicians performing a proper diagnostic procedure can help us determine the best repair that suits your vehicle.
  As you can see the Valve Body Components are a major issue that affects these types of transmissions and by replacing these solenoids and/or rebuilding the valve body can reduce the expenditures that most consumers pay to have their transmissions overhauled. We have had vehicles with severe symptoms, yet a minor repair was all it took to get back in proper operating condition. Not all transmissions can be repaired with a minor repair as some vehicles will require more repairs then others. Having your transmission checked and repaired at the first signs that your transmission is not working properly will prevent further damage and the costs will be considerably lower.