Low and spongy brake pedal

Good afternoon,

This sounds like either air in the system or a bad master cylinder. If you have done no work to it, then it sounds like the master cylinder.

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

The ABS has to be bled as well. You will need a scan tool to perform this.

Roy

ABS Automated Bleed Procedure (W/JL4)

Notice: When adding fluid to the brake master cylinder reservoir, use only Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.

Important: The following procedures may be performed on vehicles equipped with option code JL4, Vehicle Stability Enhancement System (VSES).

Pre-charge Bleed
The Pre-charge bleed procedure is to be performed when air may have been introduced into the precharge pump inlet hose, the precharge pump or the combination valve. Perform the procedure as follows.

Important: If the brake system warning lamp is illuminated, DO NOT allow the vehicle to be driven until the concern is diagnosed and repaired.

1. Ensure that the master cylinder reservoir is filled to at least the minimum-fill level with Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT 3 brake fluid from a clean, sealed container.
2. Ensure the master cylinder reservoir cap is ON securely.
3. Install a scan tool.
4. Turn ON the ignition.
5. Select the VSES Special Functions menu on the scan tool.
6. Select Pre-charge Bleed.
7. Press the On key. The precharge pump runs for approximately 3 seconds, circulating fluid from the master cylinder fluid reservoir, through the precharge pump and combination valve, then back to the master cylinder.
8. Evaluate the feel of the brake pedal. If the pedal feels spongy, perform a base brake system bleed.
9. Ensure that the master cylinder reservoir is filled to at least the minimum-fill level with Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT 3 brake fluid from a clean, sealed container.

Automated Bleed
The Automated Bleed procedure is to be performed when the brake pressure modulator valve (BPMV) is replaced. Perform the procedure as follows.

Important: The base brake system must be bled before proceeding.

Important: If the brake system warning lamp is illuminated, DO NOT allow the vehicle to be driven until the concern is diagnosed and repaired.

1. Ensure that the master cylinder reservoir is filled to at least the minimum-fill level with Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT 3 brake fluid from a clean, sealed container.
2. Ensure the master cylinder reservoir cap is ON securely.
3. Install a scan tool.
4. Turn ON the ignition.
5. Select the VSES Special Functions menu on the scan tool.
6. Select Pre-charge Bleed.
7. Press the On key. The precharge pump runs for approximately 3 seconds, circulating fluid from the master cylinder fluid reservoir, through the precharge pump and combination valve, then back to the master cylinder.
8. Select Automated Bleed.
9. Press the On key. The precharge pump and ABS pump run for approximately 6 seconds while air is purged from the BPMV.
10. Ensure that the master cylinder reservoir is filled to at least the minimum-fill level with Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT 3 brake fluid from a clean, sealed container.
11. Perform a base brake system bleed.
12. Evaluate the feel of the brake pedal. If the pedal feels spongy, repeat steps 1 - 11. If the pedal feel is acceptable, proceed to the next step.
13. Ensure that the master cylinder reservoir is filled to at least the minimum-fill level with Delco Supreme 11, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT 3 brake fluid from a clean, sealed container.