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Home >> Cadillac >> 1991 >> DeVille Base, 2D Coupe >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> BCM Flow Charts Codes F10 To F48 >> BCM Code F40, Air-Mix Door Problem >> Test Procedures

Test Procedures

NOTE: Test numbers 1 and 2 refer to test numbers on diagnostic Flow Chart (1 of 2).
  1. If Code F40 is stored and compressor clutch does not operate, then BCM's output requests are not being received by programmer over circuit No. 720, or programmer is unable to process the data. If clutch does not operate, then data is being received since both commands are sent by BCM over circuit No. 720.
  2. Operation of air-mix door can be evaluated in BCM data display by observing parameter P.2.3 while changing ECCP program number. As program number is changed from zero (maximum A/C) to 100 (maximum heat), door position should vary between its mechanical limits of travel (less than 20 percent and greater than 97 percent). Readings of 0 percent or 100 percent indicate malfunction in feedback circuit (circuit No. 733) back to BCM, while fixed or restricted readings within range of travel indicate improper door movement.
    NOTE: Test numbers 3 and 4 refer to test numbers on diagnostic Flow Chart (2 of 2).
  3. Checks circuits No. 707, 713 and 751 for a fault between BCM and programmer.
  4. Verifies programmer is receiving data from BCM. If programmer is receiving data from BCM commanding it to reposition air-mix door and does not do so, programmer is faulty. If it is not receiving data, circuit No. 720 is open or shorted, or BCM is faulty.
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