For 1990-2009 cars

### Circuit Description

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:

• | Electronic brake control module (EBCM)

• | Engine control module (ECM)

• | Transmission control module (TCM)

### Diagnostic Aids

• | If the malfunction is intermittent, check for poor connections at the suspect module. Wiggling the harness wiring may help in locating the fault.

• | Diagnostic trouble codes (DTCs) may be set do to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List 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 |

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 engine control module (ECM)

• | The transmission control module (TCM)

• | The electronic brake control module (EBCM)

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 |

1. Disconnect the scan tool from the DLC.
2. Turn OFF the ignition.
3. Disconnect all non-communicating modules on the keyword serial data circuit.
4. Turn the ignition ON, with the engine OFF.
5. 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 replaced control module if required. 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 |

1. Connect all modules and connectors.
2. Connect the scan tool to the DLC.
3. Turn ON the ignition, with the engine OFF.
4. 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