ABS/ESC Brake Solenoid Diagnostics
The ABS computer or HCU is a node on a high-speed vehicle bus. This means that the information can be typically accessed through the OBDII DLC. The ABS controller/modulator is the heart of any ABS or ESC system. The modulator gets the brake pressure from the master cylinder. Inside are the valves and solenoids that control the pressures to the wheel. During normal operation, the pressure from the master cylinder goes through the HCU unaltered.
ABS/ESC: Hydraulic Control Unit/Modulator Diagnostics
Under normal braking conditions, the master cylinder supplies fluid to the HCU and routes the pressure to the calipers. The solenoids are not energized allowing fluid to pass directly from the master cylinder to the caliper. The top solenoid is an isolation valve that isolates the HCU from the master cylinder during stability control interventions;
Tool Tip: Maximizing Tools: Diagnosing ABS/ESC Hydraulic Control Units
Brake & Front End Editor Andrew Markel finds the root cause of a brake pull using Innovative Products of America’s Brake System Analyzer.
Tech Tip: GMs, Hummers and Saabs May Experience Intermittent MIL with DTC P2138 and Reduced Power
Some customers may comment on an intermittent malfunction indicator lamp (MIL) being illuminated with a message or an indicator that displays Reduced Engine Power.
Tech Tip: Intermittent ABS Operation Caused by Cracked Sensor Ring
Rust can develop between the axle and the ABS speed sensor ring. The rust acts like a wedge and causes the ring to crack, creating a false or erratic signal that results in intermittent ABS operation.
Tech Tip: Preventing ABS Sensor Failure in Pigtail-Style Hub Assemblies
In this technical bulletin, SKF provides updated technical information for preventing ABS sensor failure in pigtail-style hub assemblies. ABS system failures that happen shortly after hub unit installation can cause concern and customer dissatisfaction. Several items should be checked during the replacement process to prevent additional unnecessary repairs.
TECH TIP: NISSAN: ABS SELF-CHECK NOISE
Each time the ignition is turned on and the vehicle is driven at about 16 mph, the ABS/VDC system performs a “Self-Check” to confirm components of the ABS/VDC system are operating correctly.
TECH TIP: GM: ABS Lamp ON/DTC C0040 Set
Some customers may comment that the ABS light is illuminated. This may be caused by the wiring harness coming in contact with the A/C compressor pulley.
Tech Tip: Audi ABS Activates Upon Light Braking
ABS activates when braking lightly or control noises are heard from the ABS unit at low speed without brake application. This may be caused if an ABS control takes place without the flashing of the ESP lamp and, therefore, without ESP operation.
Wheel Speed Sensors: ABS and TCS Signal Use
The signals from the Wheel Speed Sensors (WSS) are the most important sensor input to the Brake Control Module (BCM) for ABS activation.