Envoy 2WD V8-5.3L VIN P (2004)
Horn: Initial Inspection and Diagnostic Overview
Diagnostic Starting Point - Horns
DIAGNOSTIC STARTING POINT
Begin the system diagnosis with the Diagnostic System Check - Horns. The Diagnostic System Check will provide the following information:
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The identification of the control module(s) which command the system.
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The ability of the control module(s) to communicate through the serial data circuit.
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The identification of any stored diagnostic trouble codes (DTCs) and their status.
The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.
Diagnostic System Check - Horns
DIAGNOSTIC SYSTEM CHECK
TEST DESCRIPTION
Steps 1-5
The number(s) below refer to the step number(s) on the diagnostic table.
2. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data
circuit. The specified procedure will determine the particular condition.
3. The symptoms list in Symptoms will determine the correct diagnostic procedure to use.
4. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the
available information before tests are performed. At this point you have determined all DTCs applicable to the horn system. Refer to Symptoms -
Horns for further horn system diagnosis. Any other codes displayed from the listed modules do not apply to horns and should be diagnosed in the
applicable section. See: Symptom Related Diagnostic Procedures/A Symptoms - Horns
