Inducing Intermittent Fault Conditions
Special Tools
J-25070 Heat Gun
For equivalent regional tools, refer to
Special Tools .
Many intermittent open or shorted circuits are affected by
harness/connector movement that is caused by vibration, engine
torque, bumps/rough pavement, etc. In order to duplicate the
customer's concern, it may be necessary to manipulate the wiring
harness if the malfunction appears to be vibration related.
Manipulation of a circuit can consist of a wide variety of actions,
including:
• |
Disconnecting a connector and
reconnecting |
• |
Stressing the mechanical
connection of a connector |
• |
Pulling on the harness or wire
in order to identify a separation/break inside the
insulation |
• |
Relocating a harness or
wires |
All these actions should be performed with some goal in mind.
For instance, with a scan tool connected, wiggling the wires may
uncover a faulty input to the control module. The snapshot option
would be appropriate here. Refer to
Scan Tool Snapshot Procedure . Another option is, with the
component commanded ON and OFF by the scan tool, to move related
connectors and wiring and observe the component operation. With the
engine running, move related connectors and wiring while monitoring
engine operation. If harness or connector movement affects the data
displayed, component/system operation, or engine operation, inspect
and repair the harness/connections as necessary.
You may need to load the vehicle in order to duplicate the
concern. This may require the use of weights, floor jacks,
jackstands, frame machines, etc. In these cases you are attempting
to duplicate the concern by manipulating the suspension or frame.
This method is useful in finding harnesses that are too short and
their connectors pull apart enough to cause a poor connection. A
DMM set to the Min/Max mode and connected to the suspect circuit
while testing can yield desirable results. Refer to
Testing for Electrical Intermittents .
Certainly, using the senses of sight, smell, and hearing while
manipulating the circuit can provide good results as well.
There may be instances where circuit manipulation alone will not
meet the required criteria for the fault condition to appear. In
such cases it may be necessary to expose the suspect circuit to
other conditions while manipulating the harness. Such conditions
would include high moisture conditions, along with exceptionally
high or low temperatures. The following discusses how to expose the
circuit to these kinds of conditions.
High Temperature Conditions
If the complaint tends to be heat related, you can simulate the
condition using the J-25070 heat gun.
Using the heat gun, you can heat up the suspected area or
component. Manipulate the harnesses under high temperature
conditions while monitoring the scan tool or DMM to locate the
fault condition.
The high temperature condition may be achieved simply by test
driving the vehicle at normal operating temperature. If a heat gun
is unavailable, consider this option to enhance your diagnosis.
This option does not allow for the same control, however.
Low Temperature Conditions
Depending on the nature of the fault condition, placing a fan in
front of the vehicle while the vehicle is in the shade can have the
desired effect.
If this is unsuccessful, use local cooling treatments such as
ice or a venturi type nozzle (one that provides hot or cold air).
This type of tool is capable of producing air stream temperatures
down to −18°C (0°F) from one end and +71°C
(160°F) from the other. This is ideally suited for localized
cooling needs. In addition, circuit cooling spray can be used to
cool down a component or circuit.
Once the vehicle, component, or harness has been sufficiently
cooled, manipulate the harness or components in an effort to
duplicate the concern.
Duplicating Failure Conditions
• |
If none of the previous tests
are successful, attempt to duplicate and/or capture the failure
conditions. |
• |
Freeze Frame/Failure Records
data, where applicable, contains the conditions that were present
when the DTC set. |
|
0.1 |
Review and record Freeze
Frame/Failure Records data. |
|
0.2 |
Clear the DTCs using the scan
tool. |
|
0.3 |
Turn the key to OFF and wait
15 seconds. |
|
0.4 |
Operate the vehicle under the
same conditions that were noted in Freeze Frame/Failure Records
data, as closely as possible. The vehicle must also be operating
within the Conditions for Running the DTC. Refer to Conditions for
Running the DTC in the supporting text if a DTC is being
diagnosed. |
|
0.5 |
Monitor DTC Status for the DTC
being tested. The scan tool will indicate Ran, when the enabling
conditions have been satisfied long enough for the DTC to run. The
scan tool will also indicate whether the DTC passed or
failed. |
• |
An alternate method is to
drive the vehicle with the DMM connected to a suspected circuit. An
abnormal reading on the DMM when the concern occurs, may help you
locate the concern. |
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