"Transmission Troubleshooting"

Transmission repair can be quite expensive. Give this Transmission Troubleshooting guide a read.

You might just find a quick answer and solution to your transmission problems.

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Over Filling Transmission Fluid

Overfilling transmission fluid can cause the transmission fluid to foam up, the term for this is called cavitation. Transmission fluid cavitation happens when the transmission fluid level is too high, this causes the fluid pressure to change creating cavitation bubbles. Symptoms of a transmission cavitating are erratic shifting, internal transmission damage and oil starvation.

Low Transmission Fluid
When a transmission has low transmission fluid, this cause the transmission oil pump to run dry. Once that happens, the torque converter that creates the pressure runs dry and there is no more hydraulic pressure to the solenoids which will cause missed shifting and also erratic shifting. This causes the friction plates and clutch bands to prematurely wear at a very fast rate. You'll know this by dropping the transmission pan and feeling for any grit at the bottom. You'll feel a bunch of fibers fibrous materials. This means that you're friction plates have been destroyed. One of the most common signs with low transmission fluid is, your transmission will make a whining noise in all gears including Park and neutral. Other signs of low transmission fluid can be slipping when you push the throttle down, or while you're holding a steady RPM your transmission shifts up and down erratically on it's own. With some automatic transmissions you are able to check the transmission fluid with a transmission dipstick. Other automatic transmissions do not have dipsticks, they have a fill hole level. You fill the transmission until it begins to pour out of the hole.

Dirty Transmission Fluid
There can be a few things wrong with transmission fluid. The transmission fluid can be contaminated with metal flakes, this will cause the internals of the transmission to wear l prematurely. If the transmission fluid has a burnt smell to it or is dark black, this it can prevent the transmission from shifting properly. Now this happens because transmission hydrolic system can't build up enough hydraulic pressure to shifting the gears.

Doing a proper automatic transmission flush along with a new filter and new transmission fluid can have the transmission shifting like new again.

"Automatic Transmission Slipping When Accelerating"

Dirty Or Clogged Transmission Filter
When your transmission filter is clogged or dirty it can no longer pull the required transmission fluid consistently through the transmission oil pump to keep the solenoids operating properly. This will cause slipping,erratic shifting or not shifting at all. In some cases the vehicle won't move when you push the accelerator pedal.

Sometimes a transmission filter change can resolve this issue.
 

Bad Transmission Solenoids
Transmission solenoids are located inside the transmission. A transmission solenoids job is to direct the hydraulic fluid into the valve body to engage the correct gear. The common signs of bad transmission solenoids are erratic shifting, shift slippage and a transmission that will not shift at all. Basically when you have a bad transmission solenoid the transmission solenoid is unable to send the hydraulic pressure into the transmission valve body to select the proper gear.

Electronic Throttle Body
Now not every vehicle has an electronic throttle body, some throttle bodies are engaged by cables. For the ones that do have an electronic throttle body that's driven by a sensor in the throttle pedal, this can also be a factor. What what happens is the communication gets disrupted from the electronic throttle body to the (TCM) transmission control module causing a miss shift or no shift at all. This happens from a worn or broken dial inside the electronic throttle body. Once the dial is worn out or broken it can no longer communicate properly with the transmission control module. Now the signs of a faulty electronic throttle body can be, shifting up a gear and the back down to a lower gear or completely skipping a gear all together. Example: Going from 2nd gear to 4th gear without ever engaging 3rd gear.
 

Transmission Control Module (TCM)
Having a bad transmission control module is like having a faulty communication between your brain and the movements of your body. If the brain doesn't tell the body to do certain things the body won't react, or, it will act the wrong way. The same goes for the transmission control module, if the transmission control module isn't communicating properly to the transmission solenoids, then you will have erratic shifting, no shifting at all, or even shifting up and down erratically on its own. In some cases the transmission control module pin-out can get a little corrosive and cleaning it may resolve the issue. In rare cases a installation of the transmission control module electrical connectors can bend the pins inside, this will most definitely cause a transmission communication error. When you've exhausted all other sources, the last to do is replace the transmission control module.