Transmission Control Unit (TCU)
The TCU determines shift points and torque converter lock-up based on input signals received from throttle, position sensor, neutral safety switch, speed sensor and brake switch. The TCU controls transmission shift points and torque converter lock-up by operating electric solenoids mounted on the valve body.
The TCU contains an electronic self-diagnostic system used for determining an electronic component failure. The electronic self-diagnostic system stores a fault code if certain electronic faults exist. If fault goes away, fault code will be erased after ignition has been cycled approximately 75 times.
The TCU is located above steering column or on top left side of instrument panel (near steering column) on Grand Cherokee, or behind right side of instrument panel on other models. See Fig 1 .
Fault codes can be retrieved using a Diagnostic Readout Box (DRB-II). After repairing an electrical system problem, stored fault code must be cleared from TCU memory.