Ford Crown Victoria, Mercury Grand Marquis, Marauder, Lincoln Town Car 1999-2005

Intermittent Fault Tests


Many trouble code repair charts end with a result that reads "Fault Not Present at this Time." What this expression means is that the conditions that were present when a code set or drivability symptom occurred are no longer there or were not met. In effect, the problem was present at least once, but is not present at this time. However, it is likely to return in the future, so it should be diagnosed and repaired if at all possible.

One way to find an intermittent problem is to gather the information that was present when the problem occurred. In the case of a Code Fault, this can be done in two ways: by capturing the data in Snapshot or Movie mode or by driver observations.

The PCM has to detect the fault for a specific period of time before a trouble code will set. While intermittent problems may appear to be occasional in nature, they usually occur under specific conditions. Therefore, you should identify and duplicate these conditions. Since intermittent faults are difficult to duplicate, a logical routine (checklist) must be followed when attempting to find the faulty component, system or circuit. The tests on the next page can be used to help find the cause of an intermittent fault. Some intermittent faults occur due to a loose connection, wiring problem or warped circuit board. An intermittent fault can also be caused by poor test techniques that cause damage to the male or female ends of a connector.

Test For Loose Connectors

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To test for a loose or damaged connection, take the male end of a connector from another wiring harness and carefully push it into the "suspect" female terminal to verify that the opening is tight. There should be some resistance felt as the male connector is inserted in the terminal connection.

The Wiggle Test

A wiggle test can be used to locate the cause of some intermittent faults. The sensor, switch or the PCM wiring can be back-probed, as shown, while the test is done.

During testing, move or wiggle the suspect device, connector or wiring while watching for a change. If the DVOM has a Min/Max record mode, use this mode during the test.

Click image to see an enlarged view

Fig. Back-Probing Connector Wiggle Test Example

Diagnosis And Testing - Vehicle Does Not Fill

Pre-Mature Nozzle Shut-OffDefective fuel tank assembly components.Fill tube improperly installed (sump)
Fill tube hose pinched.
Check valve stuck shut.
Control valve stuck shut.
Defective vapor/vent components.Vent line from control valve to canister pinched.
Vent line from canister to vent filter pinched.
Canister vent valve failure (requires double failure, plugged to NVLD and atmosphere).
Leak detection pump failed closed.
Leak detection pump filter plugged.
On-Board diagnostics evaporative system leak test just conducted.Canister vent valve vent plugged to atmosphere.
Engine still running when attempting to fill (System designed not to fill).
Defective fill nozzle.Try another nozzle.
Fuel Spits Out Of Filler Tube.During fill.See Pre-Mature Shut-Off.
  At conclusion of fill.Defective fuel handling component. (Check valve stuck open).
Defective vapor/vent handling component.
Defective fill nozzle.