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 |
