802122 | Genuine Bendix® Air Brake Dash Control Valve MV-3

1. Control the Parking Brakes

• The yellow parking brake valve applies or releases the spring brakes.

• Pull knob = applies parking brakes

• Push knob = releases parking brakes (if system air pressure is sufficient)

2. Control the Trailer Air Supply

• The red dash valve supplies or cuts off air to the trailer’s brake system.

• Pull = shuts off trailer air / applies trailer emergency brakes

• Push = supplies air to the trailer

3. Operate Air-Powered Accessories

Depending on the truck, dash valves may also control:

• Lift axles

• Suspension dump

• Differential lock

• PTO (Power Take-Off)

• Auxiliary air circuits

These valves act as switches to send air pressure where it's needed.

4. Provide Safety Control

• Prevents brake release if air pressure is too low

• Ensures the trailer brakes apply automatically if air is lost

• Allows the driver to quickly apply brakes using the dash knobs in emergencies

1. Parking Brakes Won’t Apply or Release Properly

• Yellow parking brake knob doesn’t release the spring brakes

• Brakes stay applied even when the knob is pushed in

• Brakes release slowly or unevenly

2. Air Leaks at the Dash Valve

• Hissing from the back or sides of the valve

• Air escaping when knob is pulled or pushed

• Pressure loss in the primary or secondary air system

3. Trailer Brakes Don’t Respond Correctly

(For the red trailer air supply valve)

• Trailer doesn’t get air when knob is pushed

• Trailer spring brakes apply unexpectedly

• Trailer air dumps when it shouldn’t

4. Knob Pops Out Incorrectly

• Knob pops out even when air pressure is normal

• Knob will not stay pushed in
  This usually indicates an internal valve failure or weak internal spring.

5. Hard or Sticky Knob Operation

• Knob is hard to push or pull

• Feels gritty or doesn’t “click” into position
  Often caused by internal mechanical wear.

6. Truck Loses Air Pressure While Driving

• Faulty valve may bleed air from the system

• Can trigger low-air warnings or cause automatic brake application

7. Auxiliary Systems Don’t Work

(If the valve controls diff lock, PTO, suspension dump, lift axle, etc.)

• System doesn’t activate when knob is operated

• System activates intermittently

• Air pressure does not reach the component