Which statement about piggyback controllers is true?

• A. They replace the stock PCM
• B. They support only monitoring
• C. They ignore control strategies
• D. They can alter PCM input and output signals

Answer: (D)

Piggyback controllers work by sitting between the stock PCM and the engine sensors/actuators, intercepting and then altering the signals that the PCM reads or the commands it sends. This lets you tweak how the engine behaves—adjusting fueling, timing, boost, and other parameters—without removing or replacing the stock PCM. Because they integrate with the OEM system rather than replacing it, they can modify both input signals (what the PCM sees from sensors) and output signals (what the PCM commands to actuators). They’re not just monitors, and they don’t abandon the PCM’s control logic; they influence it by reshaping the signals to achieve the desired behavior.