Data Output With A Scan Tool: Overview

Data Output With A Scan Tool

The output of data relevant to OBD from the control modules was stipulated by law for the USA. It is described in SAE J 1979.

Data output is subdivided into different modes.

Mode 1
Output of:
- Input signals
- Output signals
- System status information
- Values calculated by the control module

Mode 2
Output of operating conditions (freeze frame) when a fault is stored in the memory also.

Mode 3
Output of stored faults.

Mode 4
Erase the fault memory.

Mode 5
Output of oxygen sensor data.

Mode 6
Output of test results of non-continuous tests.

Mode 7
Output of test results of continuous tests. (Output of suspected faults)

The data sets in the modes are referred to as Parameter Identification (PID).

After being stimulated by a generic scan tool, all systems relevant to OBD log on with their address. In vehicles with ME 7.2 this is the DME with the address $11 and in Tiptronic vehicles it is the transmission control module with the address $1A.

NOTE: The $ symbol means that a hexadecimal number is involved.

When the control module provides data, it also states the mode, the PID number and the address of the control module.

Example
Mode 41Pid$01 Adr$11
Engine control
No. of faults: 0
MIL commanded OFF

Data output takes place
with Mode 41 in Mode 1,
with Mode 42 in Mode 2,
with Mode 43 in Mode 3 etc.