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Chart B4, Main Relay Circuit

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1990 Pontiac Bonneville, 1990 Oldsmobile Ninety-Eight, 1990 Oldsmobile Eighty-Eight, 1990 Cadillac Fleetwood, and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
  1. Main relay provides battery voltage to EBCM to power main valve, solenoid valves, logic circuit and some self-diagnostic checks. Main relay coil receives power from EBCM pin No. 8.
  2. EBCM does not apply power to main relay coil until after EBCM receives ignition enable circuit information. Relay is grounded at left front fender. Power for main relay is through fusible link from battery junction box.
  3. Any electrical failure that prevents main relay from functioning and providing switched battery power to EBCM pins 3 and 20 will prevent EBCM from powering up. The "ANTI-LOCK" lamp remains on. The "BRAKE" lamp is not affected by this circuit.
Fig 1: Flow Chart B-4, Main Relay Circuit
G109720Courtesy of GENERAL MOTOR CO.
Fig 2: Chart B-4, Main Relay Circuit
GB0020623
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