Normal Operation and Fault Conditions

Through the use of the brake booster vacuum sensor, the ABS module monitors the vacuum in the brake booster. When the vacuum reaches the low side of a predetermined threshold, the ABS module provides a ground for the vacuum pump relay coil to activate the brake vacuum pump. Once the vacuum in the brake booster reaches the high side of a predetermined threshold, the ABS module removes the ground connection for the vacuum pump relay coil, deactivating the brake vacuum pump. 

If the sensor on the brake booster suffers an internal failure, the vacuum pump may operate continuously and one or more DTCs sets in the ABS module. If a large vacuum leak exists in the brake booster or vacuum hoses, the brake vacuum pump runs continuously. Areas of high elevation can also cause the brake vacuum pump to run continuously. Altitude affects vacuum readings, subtract 3.3863 kPa (1 in-Hg) from the reading for every 304.8 m (1, 000 ft) of elevation above sea level