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Note On Intermittents

If an intermittent DTC B120 is being set, manipulate the related wiring while observing BCM data value BD43. If the failure is induced, the reading will jump from its normal value to a reading outside the range of 5 to 95%.

NOTE: The following numbered steps refer to circled numbers on diagnostic chart. See Fig 1 . For circuit identification, see Fig 2 .
  1. BCM data value BD43 displays twilight delay time. The normal range is 5 to 95%.
  2. Check to see if the open or grounded circuit reading is due to the circuit or the switch assembly. If the open or grounded circuit reading changes to a short to voltage reading after jumpering the switch assembly terminals, the BCM and wiring are OK.
  3. Measuring the voltage between CKTs 70 (5 volts) and 271 will determine if CKT 271 is open or shorted to ground.
  4. Check to see if the short to voltage circuit reading is due to the circuit or the switch assembly. If a short to voltage reading changes to an open circuit reading after disconnecting the switch assembly, the BCM and wiring are OK.
Fig 1: DTC B120: Twilight Delay Switch Pot Circuit
G00103581Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC B120: Twilight Delay Pot Circuit Flow Chart Circuit
G00103580Courtesy of GENERAL MOTORS CORP.