lta

its function and symptoms

Accordian47

They are electro-mechanical devies meaning they are electronically controlled, switchable, mechanical devices that typically operate valves in the hydraulic system of an automatic transmission.
The activation or deactivation of a solenoid is used to change the flow rate or flow path of fluid in the transmission. This means they are used to initiate the shifting of gears because all shifting of gears in an automatic transmission is hydraulically controlled using fluid, a pump, a valvebody and valves to control clutches and the mechanical movement of other components.
The solenoids are controlled and monitored by the "PCM" or Powertrain Control Module (also referred to as the "TCM" or Transmission Control Module)
Most solenoids are mounted externally on the transmission for ease of access and are either a plastic or metal construction.
The # of terminals and wiring varies depending on the type of solenoid but they will typically have at least one power terminal (.1-12volts) and a ground terminal with some having a third terminal that is used for reference of position or validation of function by the control computer.
The PCM will detect out of range voltage or current as a problem and will store a special code in its memory.
The PCM will then also turn on a indicator light on the dash to alert you of this failure. On most Hondas this is typically seen as a flashing "D" transmission gear indicator light. Codes stored in the PCM can be read by some aftermarket scan tools or by dealer scan tools. Codes on some older models (pre-'96 I believe) can be retrieved manually be shorting two wires or terminals together and noting the # and pattern of flashes the "D" light makes.
Codes are stored for a failure of a circuit for a solenoid that is either shorted or open but can also lead to us to finding another failed component or system problem. For example, if there is a P0740 code stored in memory by the PCM than we know the PCM is seeing a problem with the Torque Converter Lock-Up Clutch Solenoid. It is seeing out of range electrical resistance, voltage or current in the circuit. Yes this means the solenoid itself could be internally or externally damaged OR it could mean the actual lock-up clutch portion of the torque converter itself has failed.

Typical Automatic Transmission Solenoids:

• Shift Solenoid (Typically 1 solenoid is responsible for 2 gears, for example there is a 1st gear-to-2nd gear shift solenoid and a 3rd gear-to-4th gear solenoid)
• Torque Converter Clutch Solenoid (Responsible for locking the torque converter clutch when certain drive parameters are met)
• Pressure Switches/Sensors

Types of Automatic Transmission Solenoids:

• Variable Force
• ON-OFF
• Pulse-Width Modulated
• Low-Leak Variable Bleed

Typical Automatic Transmission Faults Caused by Solenoids:

• Will not shift up (stays in one gear)
• Will not shift down (stays in gear)
• Will not go into gear
• Incorrect shift timing (delay in shift)