TM 5-4210-230-14&P-1 GAUGES AND INSTRUMENTS BRAKES-AIR AIR     GAUGE,     LOW     AIR     PRESSURE     BUZZER     AND INDICATOR LIGHT Should  air  pressure  in  either  section  of  the  dual  air brake  system  be  reduced  to  483      41  kPa  (70 6  psi)  the warning buzzer will sound and a light on the instrument panel will  glow.    Also,  the  air  gauge/gauges  will  indicate  low  air pressure in at least one of the independent systems. The  warning  buzzer  and  light  will  automatically  shut off   when   the   air   pressure   in   both   systems   is   sufficient, approximately 483 kPa (70 psi) to operate the vehicle. Should  the  light  and  buzzer  not  shut  off  soon  after start-up,  the  air  pressure  gauge  should  indicate  at  least  one section of the dual system has low air pressure.  If the light, buzzer and gauge indicate a loss of pressure while driving, the vehicle still has a portion of the braking capability. Under no circumstances should the vehicle continue to be operated when a failure is indicated, since air pressure cannot be built up in the system until the air leak is corrected, even  though  air  for  emergency  stopping  is  retained  in  the portion of dual air system not having a failure. ANTILOCK MONITOR (Warning) LIGHT This  light  indicates  condition  of  the  antilock  system. Refer to "Brakes Air" under Vehicle Operation. BRAKES-HYDRAULIC The  vehicle  may  be  equipped  with  either  a  single hydraulic   brake   system   (codes   04011   or   04058)   or   split hydraulic  system  (codes  04044,  04055  or  04059)  depending upon the front axle gross weight rating. There   are   two   (2)   brake   indicator   lights   (except vehicles with single system less vacuum reservoir) located on the instrument panel to determine the general condition of the hydraulic   brake   system.      They   are   "PARK   BRAKE"   and "BRAKE PRESSURE". PARK BRAKE INDICATOR (Bus chassis only) The     "PARK     BRAKE"     indicator     is     operated     in conjunction  with  the  parking  brake.    During  engine  cranking period  the  "PARK  BRAKE"  indicator  should  illuminate.    This light  will  go  out  after  engine  is  started  providing  the  parking brake is not applied.  If parking brake is applied, this light will remain on after engine has started. If light does not illuminate during cranking period the light bulb may be defective. BRAKE  PRESSURE  INDICATOR  (For  Brake  Codes  04011 and 04058 with Vacuum Reservoir Code 04510) The  BRAKE  PRESSURE  INDICATOR  in  the  single hydraulic  system  indicates  only  vacuum  supply  available  in vacuum reservoir. When  the  ignition  switch  is  turned  to  "ON"  position with engine off and no vacuum reservoir supply, the "BRAKE PRESSURE"  light  should  illuminate  indicating  that  the  light bulb is functioning.  If vehicle has a vacuum supply, pump the brake    pedal    to.        deplete    the    vacuum    supply.        BRAKE PRESSURE  INDICATOR  should  then  illuminate  with  engine off and ignition switch "ON".  After the engine has started the "BRAKE  PRESSURE"  light  should  go  off  indicating  that  the hydraulic brake system has a vacuum supply. BRAKE PRESSURE INDICATOR (For Brake Code 04044,04055,04059) When  the  ignition  switch  is  turned  to  "ON"  position with    engine    off,    the    "BRAKE    PRESSURE"    light    should illuminate indicating that the light bulb is functioning.  After the engine  has  started  the  "BRAKE  PRESSURE"  light  should  go off  indicating  that  the  hydraulic  brake  system  is  functioning properly.  Continued illumination of the "BRAKE PRESSURE" indicator  could  be  caused  by  either  a  loss  of  power  booster assist, low vacuum or a faulty condition in one side of the split hydraulic system. Should   the   "BRAKE   PRESSURE"   light   come   on during vehicle operation when the brakes are not applied, the problem is in the booster system.  If the light should come on during brake application, the problem could be either in one of the split hydraulic systems, or booster system. Should the "BRAKE PRESSURE" light illuminate, the vehicle should be operated only with the extreme caution to a repair facility due to reduced braking capability. Even if a failure should result in both the primary and backup boosters, the master cylinder alone will provide a very limited means of stopping the vehicle. CAUTION Hydraulic   brake   systems   used   on   S-Series models are power assisted. Braking capabilities   will   be   greatly   reduced   without engine   assist.      DO   NOT   MOVE   VEHICLE WITH DEAD ENGINE. 1