Install a scan tool.

Does the scan tool turn ON?

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Go to Step 2

Go to Scan Tool Inoperative

Using a scan tool, attempt to establish communications with the following systems (The Tech 2 Diagnostic Circuit Check/Class 2 Message Monitor may be used to display communication status with all systems):

Can the scan tool communicate with ALL of these systems?

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Go to Step 5

Go to Step 3

Is the scan tool able to communicate with any system?

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Go to Step 4

Go to Scan Tool Does Not Communicate with Components

Using a scan tool, attempt to establish communications with the BCM.

Important: The BCM is responsible for sending ignition position status to all systems on the serial data line. Some systems rely on ignition position status to be able to communicate. The BCM must be able to communicate properly before diagnosing any other system communication malfunction.

Can the scan tool communicate with the BCM?

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Go to Step 7

Go to Diagnostic System Check - Body Control System

Using a scan tool, check for communication DTCs. (Communication DTCs are prefixed with the letter U.)

Important: Communication DTCs do not necessarily indicate a malfunction. These DTCs are only intended to aid in diagnosing an intermittent communication malfunction that is accompanied by a symptom. If the vehicle does not experience a symptom related to a communication malfunction, these DTCs can be disregarded.

Does any system have any of the specified communication DTCs stored as current or history?

U1255

U1300

U1301

Go to Applicable DTC Table

Go to Step 6

Does any system have any communication DTCs stored as current or history?

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Go to Applicable DTC Table

System OK

Refer to the applicable Diagnostic System Check for the system unable to communicate with the scan tool.

Is the repair compete?

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Go to Step 8

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1. Turn OFF the ignition switch.
2. Reconnect or install any connector or components that were disconnected or removed.
3. Clear all communication DTCs that are set due to the communication malfunction.

Is repair complete?

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Go to Step 2

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