When a condition is not currently present, but is indicated in DTC history, the cause may be intermittent. An intermittent may also be the cause when a symptom cannot be duplicated. Most intermittent conditions are caused by faulty electrical connections or wiring. Inspect for the following items:
Wiring broken inside the insulation
Poor connection between the male and female terminal at a connector
Poor terminal to wire connection--Some conditions which fall under this description are poor crimps, poor solder joints, crimping over the wire insulation rather than the wire itself, and corrosion in the wire to terminal contact area, etc.
Pierced or damaged insulation can allow moisture to enter the wiring causing corrosion. The conductor can corrode inside the insulation, with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits.
Wiring which has been pinched, cut, or its insulation rubbed through may cause an intermittent open or short as the bare area touches other wiring or parts of the vehicle.
Wiring that comes in contact with hot or exhaust components
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 consists of performing the following actions:
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.