Intermittent failures in electronic systems may be very difficult
to detect and accurately diagnose. 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 |
History DTCs are those indicating that the heater and A/C control system
has previously detected a malfunction. The reason could be either that the
malfunction is intermittent or that the conditions for setting the DTC are
not met. Try clearing the DTCs and manually operate the system that the DTC
applies to. 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 heater and A/C control unit. The control
unit 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 heater and A/C control
operation with no DTC stored:
| • | Any condition which results in the interruption of power to the
heater and A/C control. |
| • | 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. |
