B440

Code B440 is set by the BCM if it is unable to move the air mix valve (door). The BCM requests the valve (door) to move over the data CKT 800 to the programmer. With the ignition on, the programmer supplies 5V from BCM CKT 705, to a motor which drives the air mix valve (door). The BCM monitors a feedback pot on the dc motor which varies between 0 and 5 volts depending on its position. If the valve (door) is requested to move but the feedback voltage does not change, BCM stores code B440 to indicate that the valve (door) is not responding to its command. If the air mix valve (door) feedback indicates it is near the hot or cold extreme, the code will not set if it is commanded to move to that extreme.

Operation of the air mix valve (door) can be evaluated in BCM data display by observing actual air mix valve (door) position (BD23 "ACT MIX DR") while changing the program number (override BS01 "PROGRAM NO").
1. BCM data value BD23 displays actual air mix valve (door) position. The normal range is between 1% and 99%. BCM override value BS01 is for the program number.
2. Checks to see if the fault could be due to the 5 volt reference and ground circuit or the sensor circuit.
3. Checks to see if the fault is due to the programmer or the sensor circuit.
4. Checks to see if the fault is due to the circuit or the BCM.
5. This step checks to see if the open circuit reading is due to CKT 736 or CKT 705.

Note on Intermittents
If an intermittent code B440 is being set, manipulate the related wiring while observing actual air mix door position (BD23) movement. If the failure is induced, the valve (door position will either stop or jump to an extreme value 0% or 100%). This will help in isolating the location of the malfunction.

Exit diagnostics. Select "max heat (900) and "max cool" (600) using normal HVAC controls, waiting a minimum of two minutes in each mode to see if code sets.