Possible Causes
REAR FAN SENSE SUPPLY CIRCUIT SHORTED TO GROUND
REAR FAN SENSE SUPPLY CIRCUIT SHORTED TO REAR FAN SENSE RETURN CIRCUIT
REAR FAN SENSE SUPPLY CIRCUIT OPEN
REAR FAN SENSE CIRCUIT SHORTED TO GROUND
REAR FAN SENSE CIRCUIT SHORTED TO REAR FAN SENSE RETURN CIRCUIT
REAR BOOSTER FAN REAR CONTROL SWITCH
AUTOMATIC TEMPERATURE CONTROL (ATC)