DTC P1518: TAC Module Serial Data Fault: Description
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
The Throttle Actuator Control (TAC) module and the Powertrain Control Module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity, but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.