Circuit Description
Regulations and agreements among the automobile manufacturers have resulted
in the data link connector (DLC). This connector must be used for the scan tool and
programming access to all communications systems used for those purposes on the vehicle.
The connector must have the following:
| • | A 16-pin connector configuration to which all scan tools connect |
| • | Scan tool battery power always available at pin 16 |
| • | Scan tool ground always available at pin 4 |
| • | A clean signal ground always available at pin 5 |
The rest of the pins are available for serial data communications to the vehicle
system.
The serial data circuits are the means by which the microprocessor-controlled
modules in the vehicle communicate with each other and the scan tool. There are 3
different types of protocols on this vehicle:
| • | The Universal Asynchronous Receiver Transmitter (UART) |
The scan tool accesses the following module data lines:
| • | The electronic brake control module (EBCM) (Keyword 2000) |
| • | The engine control module (ECM) (Keyword 2000) |
| • | The transmission control module (TCM) (Keyword 2000) |
| • | The inflatable restraint sensing and diagnostic module (SDM) (UART) |
| • | The intelligent switching unit (ISU) (Keyword 2000) |
| • | The speed sensitive power steering (SSPS) module (Keyword 82) |
UART DATA LINE
UART-based communication systems have a master of the serial data line and remote
transceivers. The master controls the message traffic on the serial data line by polling
all of the remotes (control modules). The master then waits for the proper response.
The UART serial data line:
| • | The UART serial data line allows the following components to communicate
data with a scan tool: |
| | The inflatable restraint sensing and diagnostic
module (SDM) |
| • | The UART serial data line allows a scan tool to communicate with these
modules for diagnosis and testing. |
Keyword 2000 Data Line
The Keyword protocols utilize a single wire bi-directional data line between
the module and the scan tool. The message structure is a request and response arrangement.
Keyword 2000 is used for scan tool diagnostics only. The modules do not exchange data
on these systems.
The Keyword 2000 serial data line:
| • | The Keyword 2000 serial data line allows the following components to communicate
data with the scan tool: |
| - | The engine control module (ECM) |
| - | The transmission control module (TCM) |
| - | The intelligent switching unit (ISU) |
| - | The electronic brake control module (EBCM) |
| • | The Keyword 2000 serial data line allows a scan tool to communicate with
these modules for diagnosis and testing. |
Keyword 82 Data Line
The Keyword protocols utilize a single wire bi-directional data line between
the module and the scan tool. The message structure is a request and response arrangement.
Keyword 2000 is used for scan tool diagnostics only. The modules do not exchange data
on these systems.
The Keyword 82 serial data line:
| • | The Keyword 2000 serial data line allows the speed sensitive power steering
(SSPS) module to communicate data with the scan tool. |
| • | The Keyword 2000 serial data line allows a scan tool to communicate with
these modules for diagnosis and testing. |
