Code B440 - A/C-Heater Air Mix Door Circuit Problem: Notes

Code B440 is set by BCM if it is unable to move air mix door. The BCM requests door to move over data circuit to programmer. The programmer then supplies 5 volts from circuit No. 705 to DC motor which drives air mix door. The BCM monitors a feedback pot on DC motor which varies between 0-5 volts, depending on its position.

If door is requested to move, but feedback voltage does not change, BCM stores code B440 to indicate that door is not responding to command. If air mix door is near its hot or cold extreme, the code will not set if door is commanded to move to that extreme. Operation of air mix door can be evaluated in BCM data display by observing actual air mix door position (BCM data code BD23) while changing program number (override value BS01) "PROGRAM NO.".

1. BCM data value BD23 displays actual air mix door position. Normal range is between 1-99 percent. BCM override value BS01 is for program number.
2. Checks to see if fault could be due to 5-volt reference and ground circuit or sensor circuit.
3. Checks to see if fault is due to programmer or sensor circuit.
4. Checks to see if fault is due to circuit or BCM.