PID (Parameter ID)
Workshop glossary › Diagnostics & protocols · UpdatedA numeric identifier for a single live data value the ECU exposes — engine RPM, coolant temperature, MAF reading. Defined by SAE J1979 mode 01.
PID stands for Parameter ID. It is the one-byte (sometimes two-byte) number a scan tool sends to ask the ECU for a specific sensor value. SAE J1979 defines around 200 standard PIDs covering everything from engine RPM (PID 0C) to oxygen sensor readings to barometric pressure.
A PID request goes out under OBD-II service 01 ("show current data") and the ECU replies with the raw value plus a conversion formula defined in the spec — for coolant temperature (PID 05) the formula is °C = A - 40, so a raw value of 0x5A (90) means 50 °C.
Manufacturer-specific PIDs live in the 0xA0+ range or behind UDS service 0x22 and require either the manufacturer's database or a tool that includes one (Autel, Launch, Texa, OEM-level).