GM 20996840 Power Brake Booster

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To perform an operating check of the power brake booster, start by depressing the brake pedal several times with the engine off to ensure there is no change in the pedal reserve distance. Next, depress the pedal and start the engine. If the pedal goes down slightly, the operation is normal. When it comes to removal, note that the power brake booster is not rebuildable, so any issues require its replacement with a new one. Begin by disconnecting the negative battery cable and the vacuum hose check valve from the power brake booster. Move the engine compartment fuse/relay box aside for clearance and remove the battery and battery tray. Once the engine is completely cool, disconnect the hose from the coolant expansion tank. Disconnect the sensor wiring harness from the master cylinder, remove the master cylinder mounting nuts, and position it aside without disconnecting the brake lines. Proceed to disconnect any electrical connectors from the booster and the electrical connector from the ABS hydraulic control unit, moving the transmission control module if needed. Put rags under the module to catch any spilled brake fluid and thoroughly clean the areas on the ABS hydraulic control unit where the hydraulic line fittings are connected. Disconnect the hydraulic lines from the ABS hydraulic control unit, making notes of their locations for reassembly, and seal all openings to prevent contamination. Depending on the model year, you'll either remove the ABS hydraulic unit mounting bracket nuts or carefully label and disconnect the brake lines from the ABS control unit and remove it along with the bracket. In the cab of the vehicle, remove the insulator panel located below the instrument panel on the driver's side (or remove the communications module and the Accelerator Pedal Position (APP) sensor on 2013 and later models). Remove the brake pedal position sensor and the clip and foam washer securing the brake booster pushrod to the brake pedal. After removing the four brake booster nuts, pull the brake booster forward and toward the middle of the engine compartment to remove it, also removing the foam seal if needed. For installation, reverse the removal steps. Lubricate the pushrod pin on the brake pedal arm with multi-purpose grease before connecting the pushrod to the brake pedal and installing the foam washer and clip. Install the ABS hydraulic control unit, tighten the mounting fasteners, bleed the brakes, and thoroughly test the brake operation before returning the vehicle to normal service.