TXD - Bus (diagnosis bus) System Operation - Voltage Waveforms

TXD bus IPO diagram

The following diagram shows components on TXD bus. Note DSC, KOM

TXD Bus

TXD bus is a single wire communication protocol used to communicate between vehicle modules and scan tools.
It operates from 0 vdc to 12 vdc.

TXD Bus Voltage Waveforms

Use the following waveforms to aid diagnosis of TXD bus
Waveforms were captured using a 16 pin OBD II breakout box connected to the DLC. A BMW GT1 scan tool was used during waveform capture.
Lapscope was connected to PIN 8 TXD bus

Click on thumbnail for larger image.

Ignition key OFF, no scan tool plugged into DLC

Ignition key OFF, with scan tool plugged into DLC

Ignition key ON, no scan tool plugged in

Ignition key ON, with scan tool plugged in

Ignition key ON, Scan tool performing Short Test

Ignition key ON, Scan tool communicating with KOM (instrument cluster)