Hydro-Max™ Brake System Inspection

Check the fluid level in the hydraulic brake fluid reservoir. If needed, fill the reservoir up to the bottom of the fill-neck. See Fig.. Use only heavy-duty brake fluid, DOT 3.

Open caps and check fluid level.

Fill to this level.

Fig. 1, Hydraulic Brake Fluid Reservoir (Bosch reservoir shown, Bendix reservoir similar)

Check all hydraulic lines and fittings for damage, leakage, or looseness.

Replace damaged or leaking components, and tighten loose fittings.

Check the brake module for leaks. If leaks are found, repair or replace the brake module. See of the Business Class M2 Plus Workshop Manual for replacement instructions, or take the vehicle to an authorized Freightliner dealer.

Check the electrical connections and harnesses. Make sure the connectors are fully seated and the harnesses are not chafed or cut. Repair or replace any damaged harness. Disconnect any loose connectors and inspect the terminals for corrosion. If corrosion is present, replace the terminals. If corrosion is not present, reconnect the connector.

Check the fuse for the hydraulic brake booster pump, as follows.

Open the cover to the main power distribution module (PDM).
Pull the fuse in position F6 for the Hydro-Max relay.
Inspect the relay to make sure the fuse is not damaged. If the fuse is damaged, install a new fuse. If the fuse is not damaged, install the fuse in position F6.
Close the PDM cover.

Check the operation of the Hydro-Max brake booster, as follows.

With the engine off, depress the brake pedal; the warning light and buzzer should come on, and the electric motor should run.
Start the engine and allow the gauges to sweep. Depress the brake pedal; no warning lights, buzzer, or electric motor should come on.

Business Class M2 Plus Maintenance Manual

Fig. 1, Hydraulic Brake Fluid Reservoir (Bosch reservoir shown, Bendix reservoir similar)