Express 1/2 Ton Van V8-305 5.0L VIN M SFI (1998)
Brake Warning Indicator: Description and Operation
Brake Warning System Operation
The brake indicator in the instrument cluster serves to alert the operator to problems in the vehicle's braking system. With the ignition switch in the RUN
or the START position, voltage flows to the Instrument Cluster from the PNK (39) wire from GAUGES Fuse 4. The BRAKE indicator lamp is
illuminated whenever the TAN/WHT (33) wire from the instrument cluster is grounded.
The BRAKE indicator lamp is tested whenever the vehicle's engine starts. Placing the ignition switch in the START position connects a ground path
from the ignition switch to ground G201 through the BLK (150) wire. With this ground connection, current flows through the TAN/WHT (33) wire to
the Daytime Running Lamp (DRL) Control Module. The DRL Control Module logic allows the current to complete the circuit, and the brake indicator
lamp is illuminated. Placing the ignition switch in the RUN position breaks the connection and the lamp goes out.
The BRAKE indicator also illuminates if you apply the parking brake while the ignition switch is in the RUN or the START position. This alerts the
operator to release the parking brake. The parking brake warning switch is mechanically grounded. The switch contacts close when you apply the
parking brake, grounding the TAN/WHT (33) wire through the Daytime Running Lamp Control Module. The DRL Control Module logic prevents the
operation of the Daytime Running Lamps while the parking brake is engaged. The Daytime Running Lamps also will not operate if either of the
following conditions is present:
^
Lamp operation by the brake pressure differential switch
^
Lamp operation by the Electronic Brake Control Module
Additionally, in vehicles equipped with the Audible Brake Warning, the Daytime Running Lamps will not operate if a low power brake booster fluid
flow and a low power brake booster pressure alarm condition is present.
The brake pressure differential switch closes its contacts when conditions in the hydraulic brake system are abnormal. This grounds the TAN/WHT (33)
wire through the BLK (150) wire to ground G103. See Antilock Brake System for detailed information about the function of this switch.
The Electronic Brake Control Module also grounds the TAN/WHT (33) circuit if there are abnormal conditions in the Antilock Brake System (ABS).
The BRAKE indicator lamp and the antilock brakes warning indicator lamp both light for ABS failures. See Section Antilock Brake System for detailed
information about the operation and grounding of the Antilock Brake System.
Vehicles with the UJ1 option code are equipped with additional brake warning equipment. On these vehicles, the P/B Booster Fluid Flow Alarm will
sound and the BRAKE indicator lamp will light if both of the following conditions are present:
^
The power brake booster fluid flow is low.
^
The brake fluid pressure is low.
Voltage is available to the P/B Booster Fluid Flow and Pressure Alarm Delay Module through the following sources:
^
The YEL (43) wire through the in-line resistor R208
^
The P/B Booster Fluid Flow Alarm YEL/BLK (965) wire
This voltage is only available when the Ignition Switch is in the ACC or the RUN position. The P/B Booster Fluid Flow Alarm does not operate unless
there is sufficient current flow through in-line resistor R208. With current flow, the voltage drop across the resistor provides the operating voltage to
drive the audible alarm. The P/B Booster Fluid Flow and Pressure Alarm Delay Module is grounded through the LT GRN (966) wire to the P/B booster
fluid pressure alarm switch. The P/B Booster Fluid Pressure Alarm Switch contacts close when fluid pressure is low. The P/B Booster Fluid Flow Alarm
Switch contacts close when fluid flow is low. Both switches will close and ground through the BLK (150) wire to Ground G112 causing the alarm to
sound.
Under normal operating conditions, in-line diode D202 prevents the park brake warning switch from providing a ground path that would cause the P/B
Booster Fluid Flow Alarm to operate. However, if the brake fluid pressure and the fluid flow are low, the diode allows the ground path to light the
BRAKE indicator lamp on the instrument cluster.
When fluid pressure and fluid flow are both low, the normally open contacts in the P/B booster fluid pressure alarm switch and the P/B booster fluid flow
alarm switch will close. The closing of these contacts provides a ground path for the P/B Fluid Flow Alarm Delay Module. The P/B Fluid Flow Alarm
Delay Module is needed because the normal start and stop operation of the brakes causes momentary low pressure conditions. The module has an
internal time delay function that prevents these short-term conditions from driving the alarm. With the P/B Fluid Flow Alarm Delay Module, low
pressure/low fluid flow conditions must exceed the normal operating limits of the system before the alarm will sound.
The alarm may occasionally sound on start-up due to low pressure and lack of fluid in the system. When the power steering pump starts operating,
pressure and flow increases to normal. This deactivates the alarm.
