Intermittents and Poor Connections

Intermittent failures in electronic Systems may be very difficult to detect and accurately diagnose. The heater A/C control tests for different malfunctions under different vehicle conditions. A through test drive is often needed in order to repeat a fault condition. If the system malfunction is not repeated during the drive test, a good description of the complaint may be useful in locating an intermittent fault condition. Faulty wires or connections cause most intermittent problems. When an intermittent 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
^ Wire chafing
^ Poor wire-to-terminal connections
^ Dirty or corroded terminals
^ Connector body damage

History Diagnostic Trouble Codes (DTCs) indicate that the heater-A/C control has previously detected a malfunction. The reason may be that the malfunction is intermittent and cannot be found easily. Try clearing the DTCs and operate the component that the DTC applies to by using a scan tool. 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-A/C control. 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 are stored.

The following conditions may result in the intermittent heater-A/C control operation with no DTCs stored:
^ Any condition which results in the interruption of power to the heater A/C control
^ The battery or ignition voltage is out of range (below 9 V or above 16 V).
^ A loose or damaged ground
^ An open or short in the Class 2 serial data link