I had this failure and the pumps are in series, it runs fine on one pump and no performance limitations. The dual pumps could be to provide reliability but they both tend to fail at the same time as mine did within days of each other. Either pump will reach full pressure with a strong battery. So there is no indication its needed to achieve high enough pressure. Old thread but I had to comment having gone through all the troubleshooting and repairs..95, 124 wagon.