The master cylinder reservoir top cap should be removed at every service interval for fluid inspection and fluid level inspection. Between services, you can simply make a quick inspection through the sight glass of the master cylinder to verify correct Harley brake fluid level.
Most importantly, the Harley brake fluid flush must be completely done and fluid replenished every two years without exception. If the DOT 4 brake fluid is not replaced every two years, the ABS control unit is prone to premature failure. DOT 4 brake fluid is very susceptible to moisture. In fact, it attracts it. For this reason, it is also very important to replace your master cylinder top cover seal if it shows signs of damage or if it has become distorted.
In this video, Mike walks you through the process of Harley brake fluid flush in the ABS system without the use of the Digital Tech or like software.
If you are not comfortable doing this service, bring the motorcycle to a professional shop or invest in the correct tools and software. Never gamble with putting your safety at risk.
If moisture is introduced into the ABS control unit, it can be an expensive repair. The valves that open and close inside of the unit can easily become stuck. If this happens, the ABS hydraulic control assembly will have to be replaced. The cost for one of these units is over $700.
The manual states that computer software is needed to correctly bleed the new module after installation. It, however, does not necessarily need to be the dealer’s Digital Technician. There are other options out there that a privately owned shop may have. However, the software is very expensive which means that you will have to pay somebody else to make this repair. The cost of the part, plus labor, is a hefty bill and nobody wants to spend $1000 and not end up with a new component or some type of a performance upgrade!
That being said, it is highly recommend that all Harley Davidson models with ABS be flushed and bled with a Digital Technician, a Centurion Super Pro, or any other software that will correctly bleed the ABS module. A lot of us hate to pay for labor when we are used to maintaining and repairing our bikes ourselves but paying for a mechanic to perform a Harley brake fluid flush once every two years is much cheaper than replacing an ABS unit.