1993 GMC Sonoma Owner's Manual - Page 170
1993 GMC Sonoma Manual
Page 170 highlights
Your Driving and the Road Brake System Warning Light Standard Cluster Digital Cluster PO159 Thislightappears on yourinstrumentcluster to warnyouifyourregular brakingsystemneedsservice. Ifyourvehiclehasrearwheelantilockbrakes, thislightwillalsowarnyouabouttroubleinthatsystem.Itwillalso light if yourparkingbrake is notfullydisengaged.SeetheIndexunder"Brake SystemWarningLight." Disc Brake Wear Indicators Yourvehiclehasfrontdiscbrakesandreardrumbrakes.Discbrakepads havebuilt-inwearindicatorsthatmakeahigh-pitchedwarningsoundwhen thebrakepadsarewornandnewpadsareneeded.Thesoundmaycome and go or be heardallthetimeyourvehicleismoving(exceptwhenyouare pushingonthebrakepedalfirmly). I The brake wearwarningsoundmeans that sooneror later your A brakes won't workwell. That could lead to an accident. When you hear the brake wear warning sound, have your vehicle serviced. A 4-1 6