This paper presents a new design of a simultaneous bidirectional PAM-4 wired transmission system that uses built-in self-test (BIST) to adjust the level of pre-emaphsis that is applied. The BIST circuitry consists of a pattern generator and detector, a signal comparator and a high-pass filter. It outputs an error indicator that is used as a control signal in the adaptive pre-emphasis block. The feedback loop inherent in a simultaneous bidirectional link provides a natural opportunity to carry information about the channel characteristics without the need for an extra dedicated wire. The design has been verified using the Cadence SpectreRF and Verilog-A simulators and the channel loss characteristics are based on an FR-4 material model extracted from the Cadence Transmission Line Model Generator.