Incident Simulation Tests

If the symptom is not present when the vehicle is brought in for service, it may be necessary for you to simulate the conditions and environment under which the incident occurred. Proceeding with a diagnosis when the vehicle is not displaying the symptom may lead the technician to a No Trouble Found Diagnosis. The following section illustrates ways to simulate the conditions/environments under which the owner experiences an electrical incident.

The section is broken into one of the six following topics:

1. Vehicle Vibration
2. Heat Sensitive
3. Freezing
4. Water Intrusion
5. Electrical Load
6. Cold or Hot Start Up

To properly simulate the condition under which the owner experiences the problem, it is important that you get a thorough description of the incident from the customer.

1. Vehicle Vibration

If the owner indicates the problem occurs or becomes worse while driving on a rough road or during periods when the engine is vibrating (idle with A/C on), you will want to check for a vibration related condition. Refer to the illustration below.

Connectors & 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. On intermittent incidents it is a good idea to disconnect, inspect and clean the terminals on related connectors in the system.

Sensors & Relays

Gently apply a slight vibration to sensors and relays in the system your inspecting. This test may indicate a loose or poorly mounted sensor or relay.








When probing a connector it is possible to enlarge the contact spring opening. Refer to figure. If this occurs it may create an intermittent signal in the circuit. When probing a connector, use care not to enlarge the opening. If the probe of the Digital Multimeter (DMM) you are using will not fit into the connector cavity, you can back probe the connector with a "T" pin to create an extension. Most DMM's have accessory alligator clips which slide over the probe to allow clipping the "T" pin for a better contact. Refer to figure. If you have any difficulty probing a terminal, inspect the terminal to ensure you have not accidentally opened the contact spring or pulled a wire loose.

Behind The Instrument Panel





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 behind or below the dash.

Engine Compartment

There are several reasons a vehicle or engine vibration could cause an electrical complaint. Some of the things to check for are:

A. Connectors which are inaccessible for diagnosis probing.
B. Connectors which may not fully be seated.
C. Wiring harness which are not long enough and are being stressed during engine vibrations or rocking.
D. Wires laying across brackets or moving components.
E. Loose dirty or corroded ground wires.
F. Wires routed too close to hot components.





To inspect components underhood, start by verifying the integrity of ground connections. (Refer to the GROUND INSPECTION described later.) Once you have assured the system is properly grounded check for loose connections by gently shaking the wiring or component as previously explained. Using the wiring diagrams in the service manual, inspect the wiring for continuity.

Under Seating Area's

If a harness is not clamped properly or has too much slack, vehicle vibration could cause the wiring to become pinched by seat components such as slide guides. If the wiring runs under seating areas inspect wiring routing for possible damage or pinching.

2. Heat Sensitive





If owner indicates the problem occurs during hot weather or after the car has sat for a short period of time, 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. Do not heat components above 60 degrees Celsius (140 Fahrenheit). If the incident occurs while heating the unit you will need to replace the component or make sure it is properly insulated from the heat source.

3. Freezing





If the customer indicates the incident goes away after the car warms up (wintertime) 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 over night. Make sure it will get cold enough to demonstrate his complaint. Leave the car parked outside overnight. In the morning, be prepared to do a quick and thorough diagnosis of those electrical components which could be affected.

The second method to diagnose for a freezing component is to put the suspect component into a freezer long enough for any water to freeze. If reinstalling the part into the car results in the incident reoccurring you will need to repair or replace that component.

4. Water Intrusion





If the incident only occurs during high humidity or rainy/snowy periods, it 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. Do not spray water directly on any electrical components.

5. Electrical Load





If the incident appears to be electrical load sensitive, perform diagnosis while all accessories are turned on including, A/C, rear defog, radio, fog lamps, etc.

6. Cold or Hot Start Up

On some occasions an electrical incident may only occur when the car is started cold or 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.