FASTECU

Docs › Connecting to the car

Bus monitor

The Bus monitor shows what is on a car's K-Line or CAN bus and lets you send messages by hand. It is mostly for reverse engineering and diagnosis.

The Bus monitor page
The Bus monitor: settings on top, the trace in the middle, the Send panel at the bottom.

Start and stop

Pick your adapter in the toolbar, choose the Interface (CAN, ISO 15765 or K-Line), set the speed and identifier size for CAN, and press Start. The adapter is connected at Start and released at Stop. Datalogging and ECU operations cannot use it while the monitor is running.

Modes

ModeWhat you see
CAN (raw frames)Every frame on the bus, any bit rate, 11 or 29-bit ids. "Put ISO-TP messages together" adds the ISO 15765 messages it finds in the frames, passively.
ISO 15765One conversation between a tester id and an ECU id (7E0 / 7E8 for SSM over CAN). The adapter takes part and answers flow control, so whole messages are seen and sent.
K-LineThe bytes on the line, cut into messages at pauses and at every SSM or KWP frame with a good checksum. Works through a J2534 or FastECU adapter, or a plain USB K-Line cable.
Listen only

With the FastECU adapter, Listen only never acknowledges and never sends, so a CAN sniffer cannot disturb the car, not even with a wrong bit rate. Use it when you are not sure of the bus.

The trace

  • Columns: time, direction, id, data, text, and a decoded info column (SSM commands and answers, UDS and KWP services, negative responses, ISO-TP frames).
  • It follows the newest row. You can pause the display without stopping the capture.
  • It keeps the last 100000 events and can be saved as CSV.
  • The id filter takes lists and ranges, and ! excludes: 7E0, 7E8-7EF, !7DF. The RX / TX / frames / messages switches narrow it too.

By id (CAN)

One row per id with its count, period and latest data. A byte that has just changed lights up, which is the fastest way to find a signal: operate something in the car and watch what changes. Click an id to show only it in the trace; shift-click to hide it.

Send

You can send:

  • K-Line bytes: as typed, wrapped in an SSM frame to the ECU or TCU, or with a checksum added.
  • A raw CAN frame, padded to 8 bytes or not.
  • An ISO 15765 message.

There are presets, a list of recent messages and a repeat interval. The preview shows the exact bytes before they go out.

Sending to a live car

Messages you send reach real control units. Do not send anything you do not understand, and never while the car is being driven.