Why do I need a power supply when programming modules?
Short answer: Programming can take a long time with the ignition on and fans, lights and modules drawing current; a dedicated power supply holds voltage steady so the flash does not fail.
During programming, the vehicle is usually in ignition-on or service mode with many modules awake. Cooling fans may run, and lights and displays stay on. Current draw can be tens of amps. A battery alone sags over a long session, and if voltage drops below what the module needs, the flash can fail and leave the module unresponsive.
A battery charger is not the same as a programming power supply. Many chargers vary their output as they move through charging stages, which can cause voltage swings. A proper power supply holds a steady voltage, often adjustable around 13 to 14 volts, and supplies enough current for the vehicle's demand.
Check the vehicle maker's requirements, since many specify voltage range and current capacity. Connect to the battery or jump terminals per the service procedure, turn off unnecessary loads, and monitor voltage throughout. Keep connections tight and clear of moving parts, and follow the supply maker's safety instructions.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.