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Home >> Buick >> 1986 >> Riviera Base >> Repair and Diagnosis >> Engine Performance >> System >> BCM System, Part II >> ECM Trouble Code Charts - Trouble Shooting >> Code B121, Twilight Enable Switch Circuit (Riviera Only) >> Note On INTERMITTENTS:
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Note On INTERMITTENTS:

If an intermittent Code B121 is being set, manipulate circuit 304. When BCM BI82 input change-of-state indicator displays an "X", check circuit for an intermittent open.

Cycle twilight control between off and maximum delay. If BCM data (BD43) does not read 6-94%, then replace left switch assembly.