Major automatic transmission components include the torque converter (a fluid coupling located between the engine and transmission), pump (creates hydraulic pressure inside the transmission for shifting and engagement), clutch packs, gear sets, valve body, shift solenoids, Transmission Control Module (TCM) (unless this function is integrated into the Powertrain Control Module or PCM), ATF fluid (different transmission require different types of ATF), fluid filter (usually located inside the transmission pan under the valve body) and external fluid cooler (often located in the radiator).
Automatic transmissions are mostly used with Rear-Wheel Drive (RWD) while automatic transaxles are used with Front-Wheel Drive (FWD). All-Wheel Drive (AWD) and Four-Wheel Drive (4WD) vehicles may use either a transmission or transaxle depending on the configuration of the drivetrain.
Electronic automatic transmissions in newer vehicles use various sensor inputs (engine RPM, throttle position, load, vehicle speed, etc.) to control gear changes.
The torque converter transfers engine torque to the transmission and multiplies torque like a set of reduction gears. Most torque converters have a “lockup clutch” that physically couples the engine and transmission in higher gears to eliminate slippage for improved fuel economy. The torque converter holds approximately one-third of the total fluid required by the transmission. A bad torque converter will prevent the engine from accelerating normally, and may cause the engine to stall when the vehicle comes to a halt.
Troubleshooting automatic transmission problems requires a scan tool to access diagnostic trouble codes, and a pressure gauge to monitor internal line pressure. If a transmission has an internal problem, it usually requires rebuilding or replacing the transmission. Fluid leaks can usually be repaired by replacing the pan gasket, or output shaft and/or input shaft seals.
Maintenance requirements are minimal, but periodic fluid and filter changes are recommended to prolong the life of the transmission.
Vehicle manufacturers have specific ATF requirements that vary by year, make and model. Using the wrong type of ATF can cause shift problems and may lead to transmission failure. Always use the type of ATF specified for the application. If using a “universal” fluid, make sure it meets the specific requirements of the vehicle manufacturer.
Required to pass this section of the P2 test:
1. Identify major automatic transmission components.
2. Identify component function and common reasons for replacement.
3 .Identify related items, including ATF fluids.
4. Provide basic use, maintenance, installation and warranty information.
