How to Repair Automatic Transmission Problems

An automatic transmission can have issues related to fluid leaks, shifting and operational errors, this guide will help sift through the easy problems and then transfer onto the more difficult issues.

What Goes Wrong?

The automatic transmission is a complex series of planetary gears, hydraulic pressure and oil control, lock up torque converter, solenoids and sensors contained inside a cast transmission case. As parts and fluid wear it can cause operational issues which could be a minor repair.

What Does it Cost?

When troubleshooting transmission problems it greatly depends on the experience of the mechanic working on the vehicle, too many times the wrong information can lead you down the incorrect path which becomes expensive. We hope to help you understand which way to go when a particular problem arises.

Lets Jump In!

Fluid Leaks are a huge issue, this repair will greatly depend on the location of the leak. If it is not clear where the leak is coming from, clean the transmission off using a degreaser such as 409 cleaner and hose off, then take the vehicle for a short drive and inspect for a leak which is done best by lifting the vehicle on jack stands. Common leak areas are the transmission pan gasket which can be fixed by performing a simple transmission service. Additional leaks can be caused by a faulty rear driveshaft seal which can be repaired by removing the driveshaft and replacing the seal which is relatively easy to do. More difficult leaks come into play when the converter seal or front pump seal are leaking because this requires the removal of the transmission. More obscure leak areas include the cooler lines, sensors or sensor O rings or the fluid cooler, which again are relativity easy to replace or repair. If the fluid level is low with no visible leaks check the radiator for fluid in the coolant, the cooler inside the radiator may be leaking and cross-contaminating the radiator coolant, the coolant will be milky pink, this will warrant a radiator replacement, cooling system service and transmission service.
transmission filter

Not Shifting, for this problem we recommend using a code scanner to see if there is a code issued for a shift control solenoid, fluid pressure sensor, input or output shaft speed sensor, P0715, P0720, P0750 or P0847. To repair sensor issues simply remove the fluid pressure sensor and replace it with a new one. A shift solenoid problem is a little more difficult because the transmission pan will need to be removed. The shift solenoid is attached to the transmission valve body and is easily changed, held on by one small screw or bolt and a wiring connector. An input/output shaft speeds sensor can be replaced externally or internally depending on the manufacturer's design.
transmission fluid pressure sensor

Won't Go Into Gear - Forward or Reverse, for this problem you must determine if the shift cable is working, in other words does the shifter feel like it is not doing anything, no detent? If so the shifter cable needs replacement. If the transmission fluid is low the hydraulic pump cannot build pressure, simply check the transmission fluid level and add as needed, if the transmission is operated for an extended amount of time with low fluid it can fail prematurely. If the fluid level is okay and there are no codes unfortunately this may be a larger problem, the unit could have failed internally such as a fluid pump or input or output shaft failure which will warrant a replacement or rebuild.
adding transmission fluid

Stuck in Park, All vehicles have a safety device called a Shift Lock Control that holds the transmissions in park gear while the key is off, and the brake pedal is not depressed. This device uses a control solenoid located near the shifter. Nine times out of then the problem will be a fuse, control solenoid or brake light switch.

Slips out of gear around a corner, this problem is easy to fix and is caused by low fluid level, with the engine warm check the transmission fluid level which should be in the safe zone of the dipstick or fill hole level.

Automatic transmissions make specific noises when a malfunction occurs, for example if the transmission filter becomes clogged due to debris, it can make a whirring noise which means the unit needs to be serviced. If the fluid level is low, you might hear a bubbling sound which is caused by the pump scavenging fluid inside the transmission pan. When a transmission has a major failure you might hear a loud "pop" which could mean a drive component inside the transmission has failed.

Transmission is slipping which is an indication or low internal fluid pressure or worn clutch discs or bands, check the condition of the fluid, some discoloration and darkening is normal as the fluid ages, but if the fluid is brown or has a burnt smell it is badly overused and a transmission service is needed which can help. If this condition is too severe the transmission will need to be removed and rebuilt or replaced.


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