Transmission Control Relay

The instant the ignition is turned "ON," the TCM performs a self-test to determine if its internal electronic circuits are all working properly. If the self-test results are good, then the TCM sends battery voltage to the Transmission Relay control circuit. The relay closes its internal contacts, which then supply battery voltage to the TCM, the four solenoids and the three pressure switches in the solenoid assembly. If the TCM "sees" a problem in the system, it turns off the power feed to the Transmission Control Relay, causing the contacts to open. A diagnostic trouble code is then stored in memory. The Transmission Control Relay is located in various places depending on the vehicle model.