ABS light and brake pedal hard to press

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If the brake pedal gets hard to push, that sounds like you are not getting power assist. What you need to do is first locate the booster. It is located under the hood and behind the master cylinder. Inspect the vacuum supply hose that runs between the engine and the booster. Picture 1 shows what the brake booster looks like.

If the vacuum supply from the engine is uninterrupted, then either the check valve that the hose attaches to at the booster is bad or the booster is bad. Pictures 2, 3, and 4 are flow charts to check for a bad booster. The easiest thing to do is simply get a vacuum gauge, draw vacuum on the booster and see if it holds vacuum. If it doesn't, it will need replaced.

To replace it you will need to remove the brake master cylinder first. There are two nuts that hold the MC on the booster. Next, disconnect the vacuum supply. Then you need to get under the dash and disconnect the push rod that connects the brake pedal to the booster. At that point, the booster will be removable from the firewall.

Let me know if you have other questions or need help. Also, if the vehicle is running rough, there could be an engine vacuum leak that is the cause of both problems. Here is a link that shows how to find a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if I can help.

Take care,
Joe