Trouble Shooting
No Brake Light Under Any Condition (Check With Ignition in "START", Cadillac, or "ON", Oldsmobile) - Burned out bulb. Blown fuse. Open electrical leads: check continuity.
Immediate Brake Light When Ignition Is "ON" - Parking brake on. Shorted parking brake switch (system OK). Fuse blown. Shorted differential pressure switch. Shorted solenoid lead to ground (blows fuses). Faulty connections or open circuit: check feed wire (pink) and connectors. Faulty Controller.
No Brake Light. System Completely Inoperative (Exercise Cycle OK; Ignition Switch "ON" Or Engine Running) - Transmission sensor seized or not being driven. Wheel sensor out of adjustment. Speed sensors shorted to each other: Disconnect sensor connectors and check resistance across terminals (should be 1000-2500 ohms); remove connectors at controller and check resistance across speed sensor connector terminals (should be infinite - open). Faulty controller.
No Brake Light. System Completely Inoperative (NO Exercise Cycle; Ignition Switch "ON" Or Engine Running) - Loss of ground lead connection from Controller: check black/white ground lead; Controller connectors unplugged. Solenoid valve seized in de-energized position: disconnect solenoid lead, momentarily apply 12 volts to solenoid terminal and listen for "click" (if no click, replace solenoid); apply 12 volts to solenoid for two to three seconds and observe if vacuum leak stops after solenoid "clicks" (if not, replace solenoid).
Brake Light Comes On After 2-5 Second Delay. System Completely Inoperative, But Exercise Cycle OK (Ignition Switch "ON" Or Engine Running) - Speed Sensor leads open: check continuity at connectors (should be 1000-2500 ohms; if not, replace Sensors); check resistance at Controller terminals (should be 1000-2500 ohms; if not, replace harness).
Speed Sensor leads shorted to ground. Modulator travel switch open: check for 0-10 ohms resistance from terminal to ground (disconnect gray wire). Modulator travel switch connector not making contact with terminal or open circuit in lead: Check continuity of switch lead; remove gray wire and insert jumper to ground (if system operates normally, travel switch is faulty). Controller faulty.
Brake Light Comes On After 2-5 Second Delay. System Completely Inoperative, And No Exercise Cycle (Ignition Switch "ON" Or Engine Running) - Solenoid leads open: Check resistance at solenoid for 3-6 ohms; remove controller and modulator harness at controller, disconnect in-line fuse (pink wire), and check continuity of terminals "C" and "D" (see illustration). Faulty controller.
False Cycling While Vehicle Is In Motion - Frayed shield leads causing intermittent short. Improperly greased sensor connector or missing clamp. Improper sensor adjustment. Bad electrical connections. Faulty controller.
False Cycling When Parked - Bad electrical connections. Faulty controller.
Does Not Cycle Down to 5 MPH During Maximum Braking Effort - Insufficient operating vacuum. Controller faulty.
Brake Light On 2-5 Seconds After High Brake Pressure Is Applies - Defective brake combination valve (excessive pressure applied to Modulator).