A PID is a Parameter IDentifier. The number following PID on the dash display defines what circuit has an issue.
Three part dash coding 101
#1) SID System Identifier - Which computer has a problem #2) PID Parameter Identifier - Which circuit on that computor has an issue #3) FMI Failure Mode Indicator - What looks wrong with the identified Parameter on the identified Computer.
MBE Engines have 2 computeres a CPC and an MCM. The MCM(aka PLD) is the Control Module is the Controler on the side of the engine. The VCU (aka CPC) is the Chassis controller.
Edit: VVVVV Thanks for setting me straight Bassman. VVVVVV
I may not know the answer but I can usually find who does.
PLD is German engineering terminology that stands for pumps, lines, and drozzles. It really refers to what we would call the individual cam driven pump units, the line and the injector nozzle which deliver fuel to each cylinder. But what I bet you are looking for is that on the older MBE906 pre-2007, they refer to what we would call the engine control unit and what they later call the MCM as a "PLD-MR." Also, instead of using a CPC as the electronic unit inside the vehicle, they called it a VCU (Vehicle Control Unit). So, normally when you hear the term PLD, it refers to the electronic control unit located on the side of the engine block. Engineers love to throw us curve balls. Hope this helps.