You would most likely want to use a piggyback controller when __________.

• A. You want to monitor data with a logger
• B. You want to alter the PCM input and output signals
• C. You want to change the PCM
• D. You want to use a handheld programmer

Answer: (B)

Piggyback controllers are added devices that sit between the PCM and the engine’s sensors and actuators, allowing you to modify what the PCM sees or commands. They work by intercepting and changing the input signals the PCM reads and/or the output signals it sends to actuators, so you can adjust fueling, timing, or other parameters without rewriting the PCM’s software. That’s why they’re best described as altering the PCM input and output signals. They aren’t primarily for data logging, which is the role of a logger, nor do they rewrite or replace the PCM software (that would be reflashing or swapping the ECU), and they’re not simply a handheld programmer used to reprogram the PCM.