Important Preliminary Checks Before Starting: Perform
Diagnostic System Check - Horns
before using the symptom tables in order to verify that all
of the following are true:
| • | The body control module (BCM) can communicate via the serial data
link. |
Visual/Physical Inspection
Several of the symptom procedures ask for a careful visual/physical
check. This step is extremely important-it could lead to correcting a problem
without further checks and can save valuable time. These checks include
the following:
| • | Inspect the easily accessible or visible system components and
harness connectors for obvious damage or conditions which could cause the
symptom. |
| • | Perform the following If the horn buzzes or has a harsh tone: |
| • | Inspect for debris in the joint where the horn fastens to the
vehicle. |
| • | Test the torque of the horn mounting hardware. The horn mounting
hardware should be tightened to a torque of 10 N·m (7 lb-ft). |
Intermittents
Important: Check for proper installation of electrical components if an intermittent
condition exists. Inspect for aftermarket theft deterrent devices, lights
and cellular phones. Ensure that no aftermarket equipment is connected
to the class 2 circuit. If you can not locate an intermittent condition,
a cellular phone signal may cause the condition. Faulty electrical connections
or wiring may also be the cause of intermittent conditions. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems.
Important: The problem may or may not turn on the SERVICE VEHICLE SOON indicator
or store a DTC. Do not use the symptom tables to diagnose intermittent conditions.
The malfunction must be present in order to locate the problem.
Poor electrical connections or wiring cause most intermittent conditions.
Perform a careful visual/physical check for the following conditions:
| • | Poor mating of the connector halves or a terminal not fully seated
in the connector body (backed out). |
| • | An improperly formed or damaged terminal. |
| • | Reform or replace connector terminals in the problem circuit in
order to insure proper contact tension. |
| • | Poor terminal to wire connection requires removing the terminal
from the connector body in order to perform the check. |
Road test the vehicle with a J 39200
digital multimeter (DMM) connected to the suspected circuit.
An abnormal voltage when the malfunction occurs is a good indication that
there is a malfunction in the circuit being monitored.
Use a Scan Tool
in
order to help detect intermittent conditions. The scan tool has several features
that can be used to locate an intermittent condition. The snapshot feature
can capture and store data parameters within the scan tool when the malfunction
occurs. This information can then be reviewed in order to see what caused
the malfunction.
Symptom List
Refer to a symptom diagnostic procedure from the following list in order
to diagnose a symptom that does not set a DTC:
