Intermittent Problem Diagnosis

Use intermittent test procedures to locate intermittent driveability problems that do not occur when the vehicle is being tested. These problems may cause a noticeable driveability problem or cause the CHECK ENGINE or SERVICE ENGINE SOON warning light to illuminate on some vehicles.

Intermittent fault testing requires the duplication of circuit or component failure in order to identify the fault. These procedures may lead to the computer recording a fault code (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, it will be necessary to monitor voltage or resistance values using a Digital Volt Ohmmeter (DVOM) while attempting to reproduce conditions that will create an intermittent fault. A change in status on the DVOM will indicate a fault has been located.

When using a DVOM or Scan tool to pinpoint faults, monitor voltage reading with ignition on or vehicle running. A change in status on the voltmeter while performing intermittent test procedures will indicate area of fault.

When using an ohmmeter to detect problems in the circuit, monitor circuit resistance (ohms) with ignition off or with battery disconnected. A change in ohmmeter reading while performing test procedures will indicate area of fault.