auto diagnostic a sound pump will spray fluid under a fairly high pressure.

How to Diagnose Automatic Transmission Problems 1First you need to know the fundamental operation of an automatic transmission GM MDI, along with the significant elements it consists of. You also should know a few of the terms and definitions linked it. To begin with, there's the Torque Converter. It is a mechanical and fluid coupling that connects the engine for the transmission. It acts like a clutch pedal inside a standard shift vehicle. Because the speed ramps up, the converter spins, multiplying the torque by a turbine style inside the unit. Early names for automatic transmissions played on this reality, employing the name "Jet" somewhere in their advertising, such as Turbojet, Hydradrive, Fluid Drive, , or Jetaway. What is important to know is that a One Way Clutch, or Sprag Clutch is used inside a torque converter. As the converter spins, it is actually allowed to overspin, or spin faster than the engine turns. This increases the output and efficiency. Because the converter slows down as the engine speed decreases, it must, at some point "catch" or stop so the engine can drive it again. This sprag clutch style lets this happen.

The converter can race away in one direction only, and catch against the one way clutch in the other.A defective sprag clutch in the converter will not allow the car to go into low or reverse. Assuming the transmission is full of clean fluid, if going into gear is very slow, or not at all, a good place to start looking for a problem would be the converter. Remove the converter by removing the transmission. Inside the converter are engagement tabs and a spline. Utilizing a couple of long screwdrivers, wedge the spline so it will hold. Try and turn the tab with the other screwdriver. It should really free spin in one direction and hold firmly in the other. If it doesn't, the converter is faulty.2Another good place to look is definitely the pump pressure if the transmission will not move at all. Although this is rare, since most pumps are very reliable diagnostics car tool, a quick check is to loosen a transmission cooling line and start the engine. Most cooling lines are at the radiator. While this is not an exacting test since a pressure gauge must be installed, a sound pump will spray fluid under a fairly high pressure. (Wrap a rag around the fitting to prevent the fluid from going everywhere). If you don't see a gusher of fluid, you have a pump problem. Only run the engine a few seconds to prevent running the transmission dry. Before you condemn the pump though, check the transmission filter. This requires removing the service pan, but it's worth the effort. A plugged or dirty filter can cause low pressure complications.It's worth noting that not all filters are serviceable. While rare, some filters are buried deep within the transmission. Check your service manual to be sure.3Another common problem is delayed shifting or harsh shifting. You can eliminate the converter and pump as being the problem. You have fluid pressure so that means the converter and pump are working. More than likely you have sticking valves in the valve body or shift solenoids. New design transmissions have computer controlled transmissions. These use electro magnets to engage or disengage shift valves.

Older transmissions used a valve body. In the older designs, it was a balancing act to determine the time to shift. A throttle valve was connected for the throttle linkage to tell the transmission where the throttle pedal was. This throttle valve was balanced against the speed from the engine via a transmission governor. The higher the speed, the greater the governor pressure. In some really old transmissions, a modulator valve took the place in the throttle valve. This relied on engine vacuum to determine load values. These load values were balanced against speed, or governor values to determine shift points. All of this went away with computers. These electromagnetic valves engage and disengage based on engine values that are computed, and these values simply determine precise shift points.If shifting is erratic, slow, or harsh, if your car is fuel injected, you probably have shift solenoids. The valves in these solenoids may be sticking. A good place to start is to service the transmission, and add a good shift conditioner. If it doesn't solve the problem, you may need to replace the shift solenoids. The same holds true for older transmissions. The valves may be sticking in the valve body or governor. If so, it's service, and/or replace the valve body and governor. It's also worth mentioning that built into the transmission, to help cushion the shifts are accumulators.

These are spring loaded dampeners. If they fail, the transmission will likely "slam" into gear. It will be a quick, neck-breaking shift, not harsh or delayed.4If you can feel your transmission shift, but then "spin out", you have challenges. This means your clutch pack or shift band has burned out. It's not good news, because this does mean an overhaul. Inside the transmission are several clutch packs and bands. There are also several more sprag, or one way clutches. The clutch packs consist of pistons that apply pressure against a "pack of friction and steel plates" that drive a sun gear, planet gear, or ring gear. (Planetary gear sets are the basis of automatic transmissions). A sure way to tell is to remove the dipstick, or drop the transmission pan and smell and inspect the fluid. If it is burnt smelling, dark and discolored, it's not a good sign.5The last failure to consider is mechanical. Sometimes a gear strips. A good way to tell is to drop the pan and look for metal shavings, metal chips, or bushing material. Bushing material is usually bronze colored. If you find this, it's time for an overhaul.