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Poor lockup action can be the result of:
electrical problems,
a malfunctioning lockup clutch assembly,
an engine problem, or
a problem in the torque converter itself.
To properly diagnose lockup converter problems, you must understand their normal operation and the controls involved with the system.
Although the actual controls of the lockup clutch assembly vary with
the different manufacturers and models of transmissions, they all will
have certain operating conditions that must be met before the lockup clutch
can be engaged.
The vehicle must be travelling at a certain speed before lockup will occur.The vehicle speed sensor sends this speed information to the computer.
The converter clutch should not be able to engage when the engine is cold, therefore a coolant temperature sensor provides the computer with information regarding temperature.
During sudden deceleration or acceleration, the lockup clutch should be disengaged.
One of the sensors used to tell the control computer when these driving modes are present is the TP sensor.
Some transmissions use a third or fourth gear switch to signal to the computer when the transmission is in that gear and to allow for converter lockup.
A brake switch is also used in some lockup circuits to disengage the clutch when the brakes are applied.
All the switches and sensors must be visually inspected. If the elcectrical system is functioning normally, then the torque coverter itself may be the problem.