P-codes, or OBD-II PIDsOn Board Diagnostics "Parameter IDs", are codes used to request data from a vehicle, used as a diagnostic tool. These codes are part of SAE standard J/1979, required to be implemented in all cars sold in North America since 1996.
Typically, an automotive technician will use PIDs with a scan tool connected to the vehicle's OBD-II connector.
The technician enters the PID
The scan tool sends it to the vehicle's bus (CAN, VPW, PWM, ISO, KWP. After 2008, CAN only)
A device on the bus recognizes the PID as one it is responsible for, and reports the value for that PID to the bus
The scan tool reads the response, and shows it to the technician
There are ten modes of operation described in the latest OBD-II standard SAE J1979. They are as follows (the 0x prefix indicates a hexadecimal radix):<br />0x01. Show current data<br />0x02. Show freeze frame data<br />0x03. Show stored Diagnostic Trouble Codes<br />0x04. Clear Diagnostic Trouble Codes and stored values<br />0x05. Test results, oxygen sensor monitoring (non CAN only)<br />0x06. Test results, other component/system monitoring (Test results, oxygen sensor monitoring for CAN only)<br />0x07. Show pending Diagnostic Trouble Codes (detected during current or last driving cycle)<br />0x08. Control operation of on-board component/system<br />0x09. Request vehicle information<br />0x0A. Permanent DTC's (Cleared DTC's)<br... Read More