One of the most problematic transmissions on the road today is an AW55-50SN Transmission. This transmission can be fitted to various vehicles from different manufacturers, including General Motors, Volvo, Saturn, Nissan, Saab, Opel, and Renault. However, these are not really 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 applyand release pressure for the torque converter clutch. By doing 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% off a major overhaul.

The component known as the “valve body” has been a major issue in these transmissions, and by knowing what corrective procedures need to be done, we have saved our customers not only time but a fair amount of monetary expenses.

In this article we will touch on some electronic sensors and valves and what they do.

One of the issues we have seen is that some people with vehicles that have this type of transmission think that adding fluid will correct their problem. The main problem with this is not knowing how to check and fill this transmission. This transmission has a 22mm “plug”which looks like the place where you should add fluids, but this “plug” is actually a band anchor. Loosening 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. It is best to let a certified and experienced transmission mechanic do this to avoid any potential mistakes or problems.

Having low or high fluid can create erratic pressure or poor linear solenoid control that can cause the TCM (transmission control module) to produce high pressure. The linear solenoids (SLT, SLS and SLU) see this high pressure reading and react accordingly, as they work at variable states dependent on the 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, based on the accelerator pedal and vehicle speed. The quality of the shift is decided by the 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 and 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, which 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” not 3 the shift and is adjusted depending on load or driving conditions.

The SLU solenoid is the torque converter lock-up pressure control solenoid. This solenoid 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 thermistor and part of the internal wiring harness assembly. The sensor has 5 volts 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 effectsensor. 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 (20 C).

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 a high or low line pressure.

Solenoid modulator valve, the SLT, the SLS, and the SLU solenoids we discussed earlier are only able to work within a set pressure. Any pressure that exceeds this amount 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 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 controls the route of fluid into the forward clutch circuit. Having a “stuck” neutral relay valve will cause a no drive or slip condition.

The torque converter clutch valve and spring prevents the cooler fluid from reversing direction.

The cooler by-pass valve prevents 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 of the complete transmission, as we did not get into the internal moving parts or hard parts of the transmission. Knowing how this transmissions works allows us at The Transmission Shop to properly diagnosis the problem and offer repairs that you would not normally hear from most shops.

With the valve body having all these solenoids and valves, chances are that the problem originated from one of those components. Our equipment is state of the art at The Transmission Shop, and you can trust our certified technicians to perform a thorough diagnostic evaluation and determine the best repair that suits your vehicle.

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, we can reduce the expenditures that most consumers pay to have their transmissions overhauled. Your entire transmission may not need to be rebuilt or even replaced, even if that’s what another mechanic told you. Before you pay another shop for this extensive work, let us check out your transmission at one of four The Transmission Shop locations in Lewisville, Garland, McKinney, or Plano.

Don’t trust just anyone with your transmission—trust only the transmission experts. Even if someone else told you that you needed an entirely new transmission, itmay only needan adjusted or replaced sensor. We have had vehicles with severe symptoms, yet a minor repair was all it took to get the vehicle back in proper operating condition. Of course, not all transmissions can be repaired with a minor procedure, as some vehicles actually will require more repairs than others, including possible transmission rebuilds or replacements. But by having your vehicle inspected and diagnosed by the experts at The Transmission Shop, you will get an honest answer as to whether or not you REALLY need to have your transmission rebuilt or replaced.

Also, you can save on out of pocket expenses by having your transmission checked and repaired at the first signs of trouble. At The Transmission Shop, we are standing by ready to serve you. Stop in today or fill out the form to the right!

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