Theory Of Operation

This diagnostic checks the amount of the accumulator's precharge pressure. Inside the accumulator there is a small bag filled with inert gas that ensures a certain amount of pressure (precharge pressure) to the hydraulic circuit. Due to normal wear of the bag, the level of precharge pressure can decrease, forcing the Electro Pump (EP) to increase its duty cycle. An excessive duty cycle will damage the EP. This diagnostic monitors the recharging time required by the EP to recharge the accumulator. If the recharging rate (change in pressure over time) is greater than a calibratable threshold and if this fault occurs for a number of times greater than a calibratable threshold in a trip, a hydraulic pressure unit accumulator fault is detected.