Dodge 2000 DURANGO Service Manual page 162

5 - 8 BRAKES
DIAGNOSIS AND TESTING (Continued)
steering, suspension, or engine components. However,
calipers that bind on the slide surfaces can generate
a thump or clunk noise. In addition, worn out,
improperly adjusted, or improperly assembled rear
brake shoes can also produce a thump noise.
BRAKE LAMP SWITCH
The brake lamp switch can be tested with an ohm-
meter. The ohmmeter is used to check continuity
between the pin terminals (Fig. 4).
SWITCH CIRCUIT IDENTIFICATION
• Terminals 1 and 2: brake lamp circuit
• Terminals 3 and 4: RWAL/ABS module and Pow-
ertrain Control Module (PCM) circuit
• Terminals 5 and 6: speed control circuit
Fig. 4 Brake Lamp Switch Terminal Identification
1 – TERMINAL PINS
2 – PLUNGER TEST POSITIONS
SWITCH CONTINUITY TEST
NOTE: Disconnect switch harness before testing
switch continuity.
With switch plunger extended, attach test leads to
pins 1 and 2. Replace switch if meter indicates no
continuity.
With switch plunger retracted, attach test leads to
pins 3 and 4. Replace switch if meter indicates no
continuity.
With switch plunger retracted, attach test leads to
pins 5 and 6. Replace switch if meter indicates no
continuity.
RED BRAKE WARNING LAMP
The red warning lamp is in circuit with the park-
ing brake switch and pressure differential switch in
the combination valve.
The red lamp illuminates when the parking brakes
are applied, or when a pressure drop occurs in the
front or rear brake hydraulic circuit.
The lamp illuminates for approximately 2-4 sec-
onds at every engine start up. This is a self test fea-
ture designed to check bulb and circuit operation.
A pressure drop in the front or rear brake hydrau-
lic circuit activates the pressure differential valve
inside the combination valve. A pressure decrease
moves the valve toward the low pressure side. As the
valve moves, it pushes the pressure differential
switch contact plunger upward. This closes the
switch internal contacts and completes the circuit to
the red warning lamp. The lamp will remain on until
repairs are made and normal fluid pressure restored.
MASTER CYLINDER/POWER BOOSTER
(1) Start engine and check booster vacuum hose
connections. A hissing noise indicates vacuum leak.
Correct any vacuum leak before proceeding.
(2) Stop engine and shift transmission into Neu-
tral.
(3) Pump brake pedal until all vacuum reserve in
booster is depleted.
(4) Press and hold brake pedal under light foot
pressure. The pedal should hold firm, if the pedal
falls away master cylinder is faulty (internal leak-
age).
(5) Start engine and note pedal action. It should
fall away slightly under light foot pressure then hold
firm. If no pedal action is discernible, power booster,
vacuum supply, or vacuum check valve is faulty. Pro-
ceed to the POWER BOOSTER VACUUM TEST.
(6) If the POWER BOOSTER VACUUM TEST
passes, rebuild booster vacuum reserve as follows:
Release brake pedal. Increase engine speed to 1500
rpm, close the throttle and immediately turn off igni-
tion to stop engine.
(7) Wait a minimum of 90 seconds and try brake
action again. Booster should provide two or more vac-
uum assisted pedal applications. If vacuum assist is
not provided, booster is faulty.
POWER BOOSTER VACUUM TEST
(1) Connect vacuum gauge to booster check valve
with short length of hose and T-fitting (Fig. 5).
(2) Start and run engine at curb idle speed for one
minute.
(3) Observe the vacuum supply. If vacuum supply
is not adequate, repair vacuum supply.
(4) Clamp hose shut between vacuum source and
check valve.
(5) Stop engine and observe vacuum gauge.
(6) If vacuum drops more than one inch HG (33
millibars) within 15 seconds, booster diaphragm or
check valve is faulty.
POWER BOOSTER CHECK VALVE TEST
(1) Disconnect vacuum hose from check valve.
DN