In aftermarket setups, what component is located between the production PCM and the control device or sensor?

• A. Tuning software
• B. Piggyback controller
• C. Hand-held controller
• D. EMS

Answer: (B)

In aftermarket setups the device that sits between the factory PCM and the sensors or actuators is a piggyback controller. It intercepts signals from sensors or the outputs from the PCM and modifies them before they reach the PCM or the actuators, then passes the altered signals along. This lets you tweak fuel, timing, or other parameters without rewiring or replacing the stock ECU. The stock PCM still runs the show, but it sees adjusted inputs or sends modified outputs thanks to the piggyback.

Tuning software operates on a computer to adjust ECU maps, not a physical component in the signal path. A hand-held controller is mainly an interface used to change settings, not the intermediary signal device. An EMS is a full engine management system that can replace the factory ECU, not sit between it and the sensors.