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Home › Cadillac › 1987 › Seville › Repair and Diagnosis › Engine Performance › System › DFI ECM Tests W/Codes › Diagnosis & Testing › Hard Code E023 - Est Circuit Problem › Failure Conditions:

Failure Conditions:

EST pulses are seen by ECM before by-pass circuit is turned on (5 volts).
EST signal remains grounded after by-pass circuit is turned on (5 volts).