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Intermittent Incident
 
 
DESCRIPTION
Sometimes the symptom is not present when the vehicle is brought in for service. If possible, re-create the conditions present at the time of the incident. Doing so may help avoid a No Trouble Found Diagnosis. The following section illustrates ways to simulate the conditions/environment under which the owner experiences an electrical incident.
The section is broken into the six following topics:
  • Vehicle vibration
  • Heat sensitive
  • Freezing
  • Water intrusion
  • Electrical load
  • Cold or hot start up
Get a thorough description of the incident from the customer. It is important for simulating the conditions of the problem.
 
 
VEHICLE VIBRATION
The problem may occur or become worse while driving on a rough road or when engine is vibrating (idle with A/C on). In such a case, you will want to check for a vibration related condition. Refer to the following illustration.
 
 
Connector & Harness
Determine which connectors and wiring harness would affect the electrical system you are inspecting. Gently shake each connector and harness while monitoring the system for the incident you are trying to duplicate. This test may indicate a loose or poor electrical connection.
 
 
Hint
Connectors can be exposed to moisture. It is possible to get a thin film of corrosion on the connector terminals. A visual inspection may not reveal this without disconnecting the connector. If the problem occurs intermittently, perhaps the problem is caused by corrosion. It is a good idea to disconnect, inspect and clean the terminals on related connectors in the system.
 
 
Sensor & Relay
Gently apply a slight vibration to sensors and relays in the system you are inspecting.
This test may indicate a loose or poorly mounted sensor or relay.
 
 
Engine Compartment
There are several reasons a vehicle or engine vibration could cause an electrical complaint. Some of the things to check for are:
  • Connectors not fully seated.
  • Wiring harness not long enough and is being stressed due to engine vibrations or rocking.
  • Wires laying across brackets or moving components.
  • Loose, dirty or corroded ground wires.
  • Wires routed too close to hot components.
To inspect components under the hood, start by verifying the integrity of ground connections. (Refer to Ground Inspection described later.) First check that the system is properly grounded. Then check for loose connection by gently shaking the wiring or components as previously explained. Using the wiring diagrams inspect the wiring for continuity.
 
 
Behind the Instrument Panel
An improperly routed or improperly clamped harness can become pinched during accessory installation. Vehicle vibration can aggravate a harness which is routed along a bracket or near a screw.
 
 
Under Seating Areas
An unclamped or loose harness can cause wiring to be pinched by seat components (such as slide guides) during vehicle vibration. If the wiring runs under seating areas, inspect wire routing for possible damage or pinching.
 
 
HEAT SENSITIVE
  • The customer's concern may occur during hot weather or after car has sat for a short time. In such cases you will want to check for a heat sensitive condition.
  • To determine if an electrical component is heat sensitive, heat the component with a heat gun or equivalent.
    cautionNever heat components above 60°C (140°F).
  • If incident occurs while heating the unit, either replace or properly insulate the component.
 
 
FREEZING
  • The customer may indicate the incident goes away after the car warms up (winter time). The cause could be related to water freezing somewhere in the wiring/electrical system.
  • There are two methods to check for this. The first is to arrange for the owner to leave his car overnight. Check it will get cold enough to demonstrate his complaint. Leave the car parked outside overnight. In the morning, do a quick and thorough diagnosis of those electrical components which could be affected.
  • The second method is to put the suspect component into a freezer long enough for any water to freeze. Reinstall the part into the car and check for the reoccurrence of the incident. If it occurs, repair or replace the component.
 
 
WATER INTRUSION
The incident may occur only during high humidity or in rainy/snowy weather. In such cases the incident could be caused by water intrusion on an electrical part. This can be simulated by soaking the car or running it through a car wash.
cautionNever spray water directly on any electrical components.
 
 
ELECTRICAL LOAD
The incident may be electrical load sensitive. Perform diagnosis with all accessories (including A/C, rear window defogger, radio, fog light) turned on.
 
 
COLD OR HOT START UP
On some occasions an electrical incident may occur only when the car is started cold, or it may occur when the car is restarted hot shortly after being turned off. In these cases you may have to keep the car overnight to make a proper diagnosis.