Data Output With A Scan Tool: Overview

DATA OUTPUT WITH A SCAN TOOL:
The output of data relevant to OBD by control units is required by US legislation for the USA and described in SAE J 1979.

Data output is subdivided into several modes:

Mode 1
Output of:
- input signals
- output signals
- system status information
- values calculated by control unit

Mode 2
Output of freeze frames if a fault is stored, Description and Operation

Mode 3
Output of stored faults.

Mode 4
Erase fault memory.

Mode 5
Output of oxygen sensor data.

The data blocks of the modes are referred to as parameter identification (PID).

After polling by a system tester, all systems relevant to OBD respond with their addresses. In the case of the Boxster, this is the DME/ECM with address $17. In the case of Tiptronic vehicles, this is the transmission control with address $1A.

If the control module outputs data, it also indicates the mode, the PID number and its address.

For example:

Mode 41Pid$01 Adr$17
Engine control
Number of faults: 0
MIL commanded OFF.

The data are outputted with mode 41 in mode 1, mode 42 in mode 2, mode 43 in mode 3, etc.