Chrysler 1991 Service Manual Supplement page 9

5 - 2 BRAKES •
Fig. 2 Vacuum Switch Location
The vacuum chamber is connected to the booster
check valve by a vacuum supply hose. A wire har-
ness connects the switch sensor to the brake warning
light. If booster vacuum falls below 8.5 inches for
8-10 seconds or more, the switch sensor completes
the circuit to the warning light causing it to illumi-
nate.
VACUUM PUMP DIAGNOSIS
Vacuum pump diagnosis involves checking pump
output with a vacuum gauge. The low vacuum warn-
ing switch can also be checked with a vacuum gauge.
Refer to the diagnosis procedure in this section.
A standard vacuum gauge can be used to check
pump output when necessary. Simply disconnect the
pump supply hose and connect a vacuum gauge to
the outlet port for testing purposes. Vacuum should
hold steady in a range of approximately 8.5 to 25
inches at various engine speeds.
DIAGNOSING LOW VACUUM OUTPUT
CONDITION
A low booster vacuum condition or a faulty low
vacuum warning switch will cause the brake warn-
ing light to illuminate. If the light does go on and in-
dicates the existence of a low vacuum condition,
check the vacuum pump, booster and warning switch
as follows:
(1) Check vacuum pump oil feed line. Verify that
line connections are secure and not leaking. If leak-
age is noted and pump is noisy, replace pump.
(2) Check vacuum pump output with a standard
vacuum gauge. Disconnect the supply hose to the
booster. Connect the gauge to this hose and run the
engine at various throttle openings. Output should
range from 8.5 to 25 inches vacuum. If vacuum is
consistently below 8.5 inches, the problem is with the
vacuum hoses or a vacuum pump component. If out-
put is within specified limits, continue testing.
(3) Check booster operation as described in the di-
agnosis section. Replace the check valve, vacuum
hoses, or booster if necessary. However, if booster op-
eration is correct but the warning light is still on,
continue testing.
(4) Disconnect the vacuum hose from the warning
switch, plug the hose and connect a hand vacuum
pump to the switch.
(5) Start and run the engine.
(6) Apply 8.5 to 9 inches of vacuum to the warning
switch and observe the warning light. If the light
goes out, the switch vacuum hose is either loose or
leaking. If the light remains on, leave the engine
running and continue testing.
(7) Apply 20-25 inches vacuum to the switch and
observe warning light operation. If the light now
goes out, the switch is at fault and should be re-
placed. If the light remains on, continue testing.
(8) Reconnect the vacuum hoses and replace the
original warning switch with a known good switch.
Run the engine and observe warning light operation.
If the light is now off, the old switch is faulty. If the
light remains on, the problem is in the wiring be-
tween the switch and warning light.
REMOVING VACUUM-STEERING PUMP
ASSEMBLY
(1) Disconnect battery negative cable.
(2) Position drain pan under power steering pump.
(3) Disconnect vacuum and steering pump hoses
from respective pumps (Fig. 3).
Fig. 3 Vacuum And Steering Pump Hose
Connections
(4) Disconnect oil pressure sender wires at sender
(Fig. 4).