Operation Manual

2.7 OBD II Modes of Operation

Here is a basic introduction to the OBD II communication protocol.

Mode byte: The first byte in the stream is the mode number. There are 9 modes

for diagnostic requests, so this first byte is from 1 to 9. The first byte in the

response data bytes is this same number plus 64. For example, a mode 1 request

would have the first data byte = 1, and the response would have the first data byte

= 65. Here is a brief description of the modes:

Mode $01 - Identifies the Powertrain information and shows current data

available to the scan tool. This data includes: DTCs set, status of on-board tests,

and vehicle data such as engine RPM, temperatures, ignition advance, speed, air

flow rates, and closed loop status for fuel system.

Mode $02 - Displays Freeze Frame data. Same data as in mode 1, but it was

captured and stored when a malfunction occurred and a DTC was set. Some of the

PIDs for mode one are not implemented in this mode.

Mode $03 - Displays the type of powertrain or emission related DTCs stored

by a 5 digit code identifying the faults. There may be more than one response

message if there are more trouble codes than will fit in the data bytes of the

response message, or if there are more than one ECU computer responding.

Mode $04 - Used to clear DTCs and Freeze Frame data. This clears all

diagnostic trouble codes that may be set including freeze frame data and readiness

monitors.

Mode $05 - Oxygen Sensor Test Results. This mode displays the oxygen sensor

monitor screen and the test results gathered about the oxygen sensor.

There are ten numbers available for diagnostics:

1. $01 Rich-to-Lean O2 sensor threshold voltage

2. $02 Lean-to-Rich O2 sensor threshold voltage

3. $03 Low sensor voltage threshold for switch time measurement

4. $04 High sensor voltage threshold for switch time measurement

5. $05 Rich-to-Lean switch time in ms

6. $06 Lean-to Rich switch time in ms

7. $07 Minimum voltage for test

8. $08 Maximum voltage for test

9. $09 Time between voltage transitions in ms

MS309 Manual_V1.01.fm Page 8 Wednesday, January 7, 2009 2:42 PM