PassThru is the working name for the J2534-defined technique where a generic interface device “passes through” communication between OEM diagnostic software on a PC and the vehicle.
The pass-thru device does no diagnosis itself — it’s a translator. Capability depends on which protocols the device implements (CAN, CAN FD, DoIP and others) and how faithfully; cheap devices fail exactly when a programming session matters most.
Why it matters
Interrupted module programming can leave a control unit unusable, so pass-thru hardware quality and a stable power supply are risk decisions, not accessories.
Related terms: J2534, VCI · Related reading: Vetting a diagnostic tool manufacturer