What P0500 usually means
P0500 means the control system has lost trust in the vehicle-speed signal it uses for shift timing, cruise control, idle strategy, and plausibility checks. On many platforms that speed value may come from a transmission output sensor, an ABS module, or a dedicated vehicle-speed sensor rather than one simple part screwed into the case. That is why P0500 can show up as a speedometer complaint on one vehicle and as harsh shifting, no upshift, or limp behavior on another.