Nissan Sentra/Pulsar/NX 1982-1996 Repair Guide

System Operation


When the ECU receives signals showing one or more wheels about to lock, it sends an electrical signal to the solenoid valve(s) within the actuator to release the brake pressure in the line. The solenoid moves to a position which allows some pressurized brake fluid to flow out of the brake line into a holding reservoir. As the wheel unlocks or rolls faster, the ECU senses the increase and signals the solenoid to re-apply hydraulic pressure. Additionally, the ECU can signal the solenoid to hold present line pressure, allowing neither increase nor decrease if the situation requires it.

This cycling occurs several times per second when ABS is engaged. In this fashion, the wheels are kept just below the point of lock-up and control is maintained. When the hard braking ends, the ECU resets the solenoids to its normal or build mode. Brake line fluid pressures are then increased or modulated directly by pressure on the brake pedal. Fluid released to the ABS reservoirs is returned to the master cylinder by the pump and motor within the actuator.

On most systems, the front wheels are controlled individually, although the Sentra and NX Coupe's system links control with the opposite rear wheel. Depending on the model, the rear wheel solenoid circuits may receive the same electrical signal or be under individual control.

The operator may hear a popping or clicking sound as the pump and/or control valves cycle ON and OFF during normal ABS operation. The sounds are due to normal operation and are not indicative of a system problem. Under most conditions, the sounds are only faintly audible. If ABS is engaged, the operator may notice some pulsation in the body of the vehicle during a hard stop; this is generally due to suspension shudder as the brake pressures are altered rapidly and the forces transfer to the vehicle.

Although the ABS system prevents wheel lock-up under hard braking, as brake pressure increases wheel slip is allowed to increase as well. This slip will result in some tire chirp during ABS operation. The sound should not be interpreted as lock-up but rather as an indication of the system holding the wheel(s) just outside the point of lock-up. Additionally, the final few feet of an ABS-engaged stop may be completed with the wheels locked; the electronic controls do not operate below approximately 6 mph.


If the vehicle is equipped with air bag or Supplemental Restraint Systems (SRS), always properly disable the system before working on or around system components.
Always use a digital, high-impedance volt-ohmmeter (DVOM) for testing unless otherwise specified. Minimum impedance should be 10 megohms.
Certain components within the ABS system are not intended to be repaired individually. Only those components with disassembly procedures should be serviced.
Do not use rubber hoses or other parts not specifically specified for the ABS system. When using repair kits, replace all parts included in the kit. Partial or incorrect repair may lead to functional problems and require the replacement of components.
Lubricate rubber parts with clean, fresh brake fluid to ease assembly. Do not use lubricated shop air to clean parts; damage to rubber components may result.
Use only DOT 3 brake fluid from an unopened container. Do not reuse drained fluid.
If any hydraulic component or line is removed or replaced, it may be necessary to bleed the entire system.
A clean repair area is essential. Always clean the reservoir and cap thoroughly before removing the cap. The slightest amount of dirt in the fluid may plug an orifice and impair the system function. Perform repairs after components have been thoroughly cleaned. Do not allow ABS components to come into contact with any substance containing mineral oil; this includes used shop rags.
The anti-lock brake controller is a microprocessor similar to other computer units in the vehicle. Ensure the ignition switch is OFF before removing or installing controller harnesses. Avoid static electricity discharge at or near the controller.
If any arc welding is to be done on the vehicle, the ABS controller should be disconnected before welding operations begin.
If the vehicle is to be baked after paint repairs, disconnect and remove the ABS ECU from the vehicle.
Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test.
Avoid touching module connector pins.
Leave new components and modules in the shipping package until ready to install them.
Always touch a vehicle ground after sliding across a vehicle seat or walking across vinyl or carpeted floors to avoid static charge damage.
Never allow welding cables to lie on, near or across any vehicle electrical wiring.
Avoid allowing extension cords for power tools or drop lamps to lie on, near or across any vehicle electrical wiring.


This is a low pressure system, No special system depressurization is necessary. Follow normal service procedure for bleeding, filling and repairs to the system.


The brake fluid reservoir is located on top of the master cylinder. While no special procedures are needed to fill the fluid, the reservoir cap and surrounding area must be wiped clean of all dirt and debris before removing the cap. The slightest dirt in the fluid can cause a system malfunction. Use only DOT 3 fluid from an unopened container. Use of old, polluted or non-approved fluid can seriously impair the function of the system.


On vehicles equipped with anti-lock brake (ABS) systems, turn the ignition switch to the OFF position and disconnect the negative battery cable. All other steps apply to both ABS and conventional brake systems.

For the specific procedure, refer to bleeding of the conventional brake system as outlined in this section.