Can be a common data chatter problem where the TAC is fine but data to or from it gets wacked on the data bus so it is wrongly assumed TAC is failing.

Common when flashing like the PCM that hogs the Starbus while TAC tries to send out a keepalive frame but bus is too busy with all the flash data frames and falsely trips a P1518 and why GM content says at times this P1518 DRC can be ignored.

If clearly the DTC a few times does not clear the error then issue has to be looked into with more depth.