Inducing Intermittent Fault Conditions: Notes

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:

• Wiggling the harness.
• 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. See SCAN TOOL USAGE for advanced intermittent diagnosis. 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 Digital Multi-Meter (DMM) set to Peak Min/Max mode and connected to the suspect circuit while testing can yield desirable results. See 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.