LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2006 >> STS V >> Repair and Diagnosis >> External Pages >> Different car >> Section 17 (Data Communication System) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Keyword Data Line >> Circuit Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit Description

WARNING: This page is about a different car, the 2007 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.

The Keyword protocol utilizes a single wire bi-directional data line between the modules and the scan tool. The message structure is a request and response arrangement. Keyword serial data is used for scan tool diagnostics only. The modules do not exchange data on this circuit.

The following modules are connected to the Keyword serial data circuit:

Scan Tool Does Not Communicate with Keyword Data Line

Step Action Yes No
Schematic Reference:  LINK
Connector End View Reference:  Master Electrical Component List  and  Inline Harness Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2
  1. Connect the scan tool to the data link connector (DLC).
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with each module on the keyword serial data circuit:
    • The headlamp - left
    • The headlamp - right
Does the scan tool communicate with all the modules on the keyword serial data circuit?		 Go to Testing for Intermittent Conditions and Poor Connections Go to Step 3 
3
  1. Disconnect the scan tool from the DLC.
  2. Disconnect all non-communicating modules on the keyword serial data circuit.
  3. Test the keyword serial data circuit between the DLC and all the modules on the keyword serial data circuit, for the following conditions:
    • An open
    • A short to ground
    • A short to voltage
Refer to the following:Did you find and correct the condition?		 Go to Step 7  Go to Step 4 
4 Test the following circuits of the module that is not communicating for an open or high resistance:
  • The battery positive voltage input circuits
  • The battery positive voltage output circuits
  • The ignition voltage input circuits
  • The ignition voltage output circuits
  • The switched battery positive voltage supply circuits
  • The ground circuits

Refer to the following:
Did you find and correct the condition?		 Go to Step 7  Go to Step 5 
5 Inspect for poor connections and terminal tension at the following harness connector circuits, of the module that is not communicating :
  • The battery positive voltage input circuits
  • The battery positive voltage output circuits
  • The ignition voltage input circuits
  • The ignition voltage output circuits
  • The switched battery positive voltage supply circuits
  • The ground circuits
  • The Keyword serial data circuits

Refer to the following:
Did you find and correct the condition?		 Go to Step 7  Go to Step 6 
6 Replace the module that is not communicating on the Keyword serial data circuit. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 7  -
7
  1. Connect all modules and connectors.
  2. Connect the scan tool to the DLC.
  3. Turn ON the ignition, with the engine OFF.
  4. Retrieve the DTCs.
Did you record any current DTCs?		 Go to Diagnostic Trouble Code (DTC) List - Vehicle Clear all history DTCs
System OK
scientia non olet · About LEMON Manuals