Q:

What is an automatic transmission valve body?

A:

Quick Answer

An automatic transmission valve body is a major component of a vehicle's automatic transmission system and directs pressurized transmission fluid to a network of valves that engage appropriate clutch packs for smooth gear shifting. These valves use pressure as hydraulic signals to determine which gear set, also called band servo, to select when the vehicle changes speed.

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Full Answer

The valves inside the transmission valve body receive pressurized hydraulic fluid from the hydraulic pump, called the governor, to drive clutch and brake actuators for optimal band servo ratio. The most important of these valves is the manual valve. It is directly connected to the gear stick handle and instructs which passages should allow hydraulic fluid to pass through.

Modern automatic transmission systems incorporate sensors that monitor car speed, throttle position, brake pedal position and engine load to control how soft or firm the gear shift must be. The sensors send vital data to the onboard engine management computer, which directs electrically controlled solenoids that redirect hydraulic fluid to the correct clutch pack.

The incorporation of these sensors has made self-diagnostics possible on modern transmission systems. A malfunctioning transmission part is detected early by the engine management computer which, in turn, alerts drivers by activating a warning light on the vehicle's dashboard.

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Related Questions

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    How do you diagnose problems with an automatic transmission?

    A:

    To diagnose automatic transmission problems, check for a low transmission fluid level, which leads to poor shifting of a vehicle and gradually causes damage to the transmission, and check for leaks in the filler tube base, the drain hole below the transmission, and the area between the engine and transmission. Also check for a clogged filter, and replace the filter if necessary.

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  • Q:

    What happens if the transmission fluid does not get refilled?

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    If a vehicle's transmission system runs out of fluid and it is not replaced, the moving parts within the transmission and engine can grind against each other and cause irreparable damage to the system. Transmission fluid should also be changed on a regular basis to ensure proper working conditions.

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    What is a shift solenoid B malfunction?

    A:

    A shift solenoid B malfunction is the failure of shift solenoid B in an automatic transmission to reroute the transmission fluid's flow that changes the shift valves' positions in the valve body. The failure prevents the transmission shift from second to third gear. A powertrain computer displays OBD II trouble code P0755 when the number of revolutions per minute does not change because the transmission did not shift, and the vehicle's speed sensor does not show a road speed increase.

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  • Q:

    What happens if you overfill transmission fluid?

    A:

    Overfilling an automatic transmission causes the fluid to foam, leading to erratic gear shifting, oil starvation and transmission damage. Overfilling a manual transmission causes the fluid to leak from the vent and the gear trains to slow down when the clutch is depressed, leading to gear shifting problems.

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