Circuit Description

WARNING: This page is about a different car, the 2004 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:

Engine Control Module (ECM)
Transmission Control Module (TCM) w/M82
Headlamp Assembly-LF w/export
Headlamp Assembly-RF w/export

Scan Tool Does Not Communicate with Keyword Data Line

Step	Action	Yes	No
Schematic Reference: Data Link Connector (DLC) Schematics Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems
1	Did you perform the Diagnostic System Check for the system exhibiting symptom?	Go to Step 2	Go to Control Module References in Body Control System for the applicable Diagnostic System Check
2	Connect the scan tool to the DLC. Turn ON the ignition, with the engine OFF. Attempt to communicate with each module on the keyword serial data circuit: The engine control module (ECM) The transmission control module (TCM) The headlamp assembly - LF w/export The headlamp assembly - RF w/export Does the scan tool communicate with all the modules on the keyword serial data circuit?	Go to Testing for Intermittent Conditions and Poor Connections In Wiring Systems	Go to Step 3
3	Disconnect the scan tool from the DLC. Disconnect all non-communicating modules on the keyword serial data circuit. 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: Control Module References in Body Control System for the applicable schematic Circuit Testing in Wiring Systems Wiring Repairs in Wiring Systems. 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: Control Module References in Body Control System for the applicable schematic Circuit Testing in Wiring Systems Wiring Repairs in Wiring Systems 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: Control Module References in Body Control System for the applicable schematic Testing for Intermittent Conditions and Poor Connections in Wiring Systems Connector Repairs in Wiring Systems Did you find and correct the condition?	Go to Step 7	Go to Step 6
6	IMPORTANT: Perform the programming or set up procedure for the module if required, after it is replaced. Replace the module that is not communicating on the Keyword serial data circuit. Refer to Control Module References in Body Control System for the applicable replacement procedure.Did you complete the replacement?	Go to Step 7	-
7	Connect all modules and connectors. Connect the scan tool to the DLC. Turn ON the ignition, with the engine OFF. Perform the Diagnostic System Check for the system exhibiting symptoms. Refer to Control Module References in Body Control System. Did you complete the operation?	System OK	Go to Step 2