B440

Code B440 - HVAC - Air Mix Door Circuit:

Wiring Diagram for Code B440 - Air Mix Door Circuit Problem:

CODE B440 - AIR MIX DOOR CIRCUIT PROBLEM

Circuit Description:

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


Test Description:

1. BCM data value BD23 displays actual air mix door position. The normal range is between 1% and 99%. BCM override value BS01 is for the program number. As the program number is changed from 0 (max A/C) to 99 (max heat), the door position should vary between its mechanical limits of travel.

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.



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 door position will either stop or jump to an extreme value (0% or 99%). This will help in isolating the location of the malfunction.

Exit diagnostics. Select "MAX HEAT" and "MAX COOL" using normal HVAC controls, waiting a minimum of two minutes in each mode to see if code sets.