SD-13-4958
Bendix® M-40QR™ & M-40HF™ Pressure Modulator Valves
Bendix® M-40QR™
Modulator
(Height = 3.75”)

Bendix® M-40HF™
Modulator
(Height = 4.75”)

Delivery Port
(Casting has
“2, DEL”)

Supply Port
(Casting has
“1, SUP”)

Supply Port
(Casting has
“1, SUP”)

Alternate Push-toConnect Version,
Showing Optional
Packard Connector

Electrical
Connector
Electrical
Connector

Exhaust Port
(Body has
“3, EXH”)

Mounting Holes
(.33" Diameter
Through Body)

Exhaust Port
(Body has
“3, EXH”)

OE and Service New Bendix® M-40QR™
and M-40HF™ modulator valves
manufactured after February 2014,
contain two parallel ribs on each side of
the Supply and Delivery ports as shown
here. These ribs identify these modulators
as a genuine Bendix® product. If the OE
or Service New valve was manufactured
after this date and does not contain these
ribs, it is not a genuine Bendix® product.

Figure 1 - M-40QR™ & M-40HF™ Pressure Modulator Valves

DESCRIPTION
The Bendix® M-40QR™ (quick release) and M-40HF™ (high
flow) pressure modulator valves (PMVs) are high-capacity,
on/off air valves that incorporate a pair of electrical
solenoids for control. See Figure 1. The solenoids provide
the electro-pneumatic interface between the vehicle’s
electronic control system and the air brake system. For
example, the PMV is used to control the braking function
of service actuators during antilock activity.

Bendix® M-32QR™
Modulator

Bendix® M-32™
Modulator

Figure 2 - Previous Bendix® M-32™ Modulators

1

GENERAL SAFETY GUIDELINES

WARNING! PLEASE READ AND
FOLLOW THESE INSTRUCTIONS
TO AVOID PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following
guidelines should be observed AT ALL TIMES:
▲Park the vehicle on a level surface, apply the parking
brakes and always block the wheels. Always wear personal
protection equipment.
▲Stop the engine and remove the ignition key when working
under or around the vehicle. When working in the engine
compartment, the engine should be shut off and the ignition
key should be removed. Where circumstances require that
the engine be in operation, EXTREME CAUTION should be
used to prevent personal injury resulting from contact with
moving, rotating, leaking, heated or electrically-charged
components.
▲Do not attempt to install, remove, disassemble or
assemble a component until you have read, and thoroughly
understand, the recommended procedures. Use only the
proper tools and observe all precautions pertaining to use
of those tools.
▲If the work is being performed on the vehicle’s air brake
system, or any auxiliary pressurized air systems, make
certain to drain the air pressure from all reservoirs before
beginning ANY work on the vehicle. If the vehicle is
equipped with a Bendix® AD-IS® air dryer system, a Bendix®
DRM™ dryer reservoir module, or a Bendix ® AD-9si ® air
dryer, be sure to drain the purge reservoir.
▲Following the vehicle manufacturer’s recommended
procedures, deactivate the electrical system in a manner
that safely removes all electrical power from the vehicle.
▲Never exceed manufacturer’s recommended pressures.
▲Never connect or disconnect a hose or line containing
pressure; it may whip and/or cause hazardous airborne
dust and dirt particles. Wear eye protection. Slowly open
connections with care, and verify that no pressure is
present. Never remove a component or plug unless you are
certain all system pressure has been depleted.
▲Use only genuine Bendix ® brand replacement parts,
components and kits. Replacement hardware, tubing, hose,
fittings, wiring, etc. must be of equivalent size, type and
strength as original equipment and be designed specifically
for such applications and systems.
▲Components with stripped threads or damaged parts should
be replaced rather than repaired. Do not attempt repairs
requiring machining or welding unless specifically stated
and approved by the vehicle and component manufacturer.
▲Prior to returning the vehicle to service, make certain all
components and systems are restored to their proper
operating condition.
▲For vehicles with Automatic Traction Control (ATC), the ATC
function must be disabled (ATC indicator lamp should be
ON) prior to performing any vehicle maintenance where
one or more wheels on a drive axle are lifted off the ground
and moving.
▲The power MUST be temporarily disconnected from the
radar sensor whenever any tests USING A DYNAMOMETER
are conducted on a vehicle equipped with a Bendix ®
Wingman ® system.
▲You should consult the vehicle manufacturer's operating
and service manuals, and any related literature, in
conjunction with the Guidelines above.
2

The modulator consists of a die cast metal and plastic body
that houses one normally-open solenoid, one normallyclosed solenoid, and an inlet and exhaust diaphragm
valve. A three-pin weather-resistant electrical connector
is an integral part of the modulator solenoid assembly
and delivers the vehicle controller’s commands to the
modulator. Two mounting holes are provided for frame or
crossmember mounting of the valve.
The Bendix® M-40QR™ modulator is the direct replacement
for the Bendix® M-32QR™ modulator (See Figure 2). The
Bendix M-40QR modulator has a bias valve to provide an
internal quick-release function.
The supply, delivery, and exhaust ports on the Bendix M-40
modulators have embossed identification codes.
Air Hose
Port ID Connection

Function

1, SUP

Supply

Air enters from a valve (typically
foot, relay, or quick release).

2, DEL

Delivery

Air is delivered to the service
actuators.

3, EXH

Exhaust

Air is vented to the atmosphere.

Figure 3 - Port Designation and Function

APPLICATIONS
Bendix M-40™ modulators may be used for various purposes
on a vehicle, including ABS and stability interventions. In
applications using these PMVs, an external quick release
valve may also be required, depending on the system
design. Where the modulator is used for individual wheel
control applications, it is typically the last control valve
through which air passes on its way to the service brake
actuator. See Figure 4 for a typical system schematic.

PRESSURE MODULATOR VALVE (PMV) AND
TRACTION CONTROL VALVE (TCV) CHUFF TEST
A wiring harness connects the vehicle modulators to the
controller. The ABS controller is able to simultaneously,
and independently, control the individual modulators.
Bendix® Electronic Control Units (ECUs) perform a Bendixpatented PMV and TCV Chuff Test. The Chuff Test is
an electrical and pneumatic PMV test that can assist
maintenance personnel in verifying proper PMV wiring and
installation. This test is performed only when the vehicle
is stationary (if the vehicle moves, the Chuff Test will not
be performed).
NOTE: If there are any active Diagnostic Trouble Codes
(DTCs), the stop lamp cross-check portion of the Chuff Test
will not be carried out until all DTCs are fully diagnosed and
corresponding repairs are successfully conducted. The
ESP/ATC dash indicator lamp ATC/ESP Lamp – a lamp that
indicates when stability functions, including traction control,

SL-4™ Stop Light Switch
TP-5™ Tractor
Protection Valve
Wheel Speed
Sensor

TCS-9000
Trailer
Control
Valve

Air Disc
Brake

™

Pressure
Modulator
Valve

C
S

Antilock
Controller

Primary
Brake
Circuit
Brake
Valve

Pressure
Modulator
Valve

Secondary
Brake
Circuit

Pressure Modulator Valve
Antilock Relay Valve

Yaw Rate
Sensor

Pressure Modulator Valve
Wheel Speed
Sensor

Spring
Brake
Chamber

Slack Adjuster
Service Brake
Chamber
Foundation Drum
Brakes

Trailer
(Supply)

Service &
Spring Brake
Chamber

Steering
Angle Sensor

Antilock
Traction
Relay
Valve

Trailer
(Control)

Wheel Speed
Sensor

Air Disc
Brakes

Service
Brake
Chamber
Pressure
Modulator
Valve

Glad Hands

Foundation
Drum Brakes
Primary
Brake Circuit

Secondary
Brake Circuit

For Illustration Purposes Only, Both
Air Disc Brakes And Foundation
Drum Brakes Are Shown At Either
Side Of The Axles.

Figure 4 - Typical System Diagram (4S-4M System Shown)
roll stability program, or yaw control are operating – will also
be illuminated when there are active ABS, ATC, or ESP
DTCs. (See the Glossary on page 8 for more information
on these terms.)
See Figure 5. When ignition power is applied, each
modulator solenoid is briefly energized. If the air system
is fully charged – and the service brake pedal is depressed
during ignition – the modulator creates a single, sharp
audible “chuff” of air pressure. Bendix ECUs will perform
a PMV Chuff Test on all installed modulators in the order
shown in Figure 5. The pattern will then repeat itself.

Right Steer
1
2

Right Drive

Right
Additional

3

5

4

6

Left Drive

Left
Additional

7

Driver

Left Steer
1. Steer Axle Right PMV
2. Steer Axle Left PMV
3. Drive Axle Right PMV
4. Drive Axle Left PMV

5. Additional Axle Right PMV
6. Additional Axle Left PMV
7. Trailer PMV

Figure 5 - Typical Vehicle Orientation and Chuff
Sequence
3

If equipped with a Bendix® EC-60™ (or later) advanced
controller, following the completion of the second round
of PMV & TCV Chuff Tests, the controller (if configured to
do so) will perform a test to cross-check the trailer PMV
operation with the vehicle stop lamps. If the trailer
PMV circuit is mis‑wired (including the steer axle TCV),
the PMV will exhaust a large amount of air, or none at all.

GENERAL
See Figure 6.
The first four rows of this table show normal vehicle braking
where the PMV does not intervene. In the case of a
rapid, non-antilock release of the brakes (e.g. if the driver
releases the brakes after a severe brake application), the
Bendix® M-40QR™ PMV assists the quick release of the
brakes by being the point at which the air is exhausted.
The final four rows of the table show the actions taken
during an antilock braking event.

OPERATION
Mode

ANTILOCK OPERATION

Modulator
Type

Hold
Solenoid
State

Exhaust
Solenoid
State

Description

Antilock Braking

Normal Braking

Normal,
Air pressure supplied to the modulator exits
Non-Antilock,
HF and QR De-energized De-energized the modulator delivery port and flows to the
Brake Application
service brake chambers.
Non-Antilock
Hold

When the desired air pressure is attained in
HF and QR De-energized De-energized the service brake chambers, the air pressure
in the system levels off.

Normal,
Non-Antilock,
Relatively “slow”
Brake Release

Air from the brake chambers moves back
through the modulator in the reverse
direction as it flowed during application.
HF and QR De-energized De-energized
Simultaneously, a small amount of air will
generally be expelled from the modulator
exhaust port.

Rapid,
Non-Antilock,
Exhaust
(e.g., the driver
releases the
brakes after a
severe brake
application)

QR

The internal bias piston blocks air from the
brake chamber from moving back through the
De-energized De-energized
modulator. Instead, all the air is exhausted
out the modulator exhaust port.

HF

Air from the brake chambers moves back
through the modulator in the reverse
De-energized De-energized direction as it flowed during application.
Simultaneously, air will be expelled from the
modulator exhaust port.

Antilock Apply

Air pressure supplied to the modulator exits