Intermittent failures in electronic systems may be very
difficult to detect and accurately diagnose. The DCM tests for different malfunctions
under different vehicle conditions. For this reason, a thorough test
drive is often needed in order to repeat a fault condition. If the system
malfunction is not repeated during the test drive, a good description
of the complaint may be useful in locating an intermittent malfunction.
Faulty wires or connections cause most intermitting problems. When an
intermitting condition is suspected, inspect the suspected circuits
for the following conditions:
| • | Poor mating of connector halves of backed out terminals |
| • | Improperly formed or damaged terminals |
| • | Poor wire to terminal connections |
| • | Dirty or corroded terminals |
The DCMs has the ability to store DTCs as history codes only. Therefore,
when a DTC is stored , the DCMs will display all DTCs as history even thought
the malfunction maybe current. Always diagnose history DCM DTCs the same
way as current DTCs by performing the applicable DTC table. History DTCs
are those indicating that the DCM is currently detecting or has previously
detected a malfunction. The reason could be either that the malfunction
is intermittent or that the system for which the DTC is set for is not
currently being operated. For example, the DCMs cannot detect a malfunction
in the power window motor circuit until the window is operated. For this
reason, if the DCM displays a history DTCs associated with the window motor
circuit and the malfunction cannot be found easily, try clearing the DTCs
and manually operating the system that the DTC applies to using a scan
tool. Operating the system with a scan tool while moving wiring or connector
may recreate the conditions required to set the DTC. Read the Diagnostic
Aids and Conditions for Setting the DTC in each DTC table for more specific
information.
History DTCs help in diagnosing intermittent fault conditions but do
not necessarily indicate a faulty DCM. The DCM is a reliable component, and
is not the likely cause of the malfunction. Most system complaints are
linked to faulty wiring and connectors, and occasionally to a component.
Perform a thorough inspection of all related wiring and connectors pertaining
to the history DTC that is stored.
The following conditions may result in intermittent DCM operation with
no DTC stored:
| • | Any condition which results in the interruption of power to the
DCM |
| • | The battery or ignition voltage is out of range (below 9.0 volts
or above 16.0 volts). |
| • | A loose or damaged ground |
| • | An open or a short on the serial data line |
