brake pedal was very stiff

Hi and thanks for using 2CarPros.com. If it is doing the same thing, it does not sound like a booster problem. For the booster to operate properly, it needs eighteen inches of vacuum from the engine. Remove the vacuum hose to the booster and check if you are getting that. If you are not suspect there is a plug in the hose, a cracked hose, or another vacuum leak causing engine vacuum to drop.

Here are directions for checking engine vacuum and how to identify a leak:

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

Try this first and let me know what you find.

Take care,

Joe

Will a vacuum leak cause the brake pedal to get very hard an not let the vehicle stop?

Hi again. The reason the pedal is normally easy to press is because of engine vacuum in the brake booster. If there is a leak, you may not get the assist. Hence, it is hard to press.

I checked the vacuum hose going to the booster an it is still good. There is lots of vacuum. Would a bad ABS module cause this?

Hi, honestly the module would not cause this. Have you checked intake vacuum with a gauge to determine if it is adequate?

After thought. Is there a white one way valve on the booster where the vacuum hose connects? If so, remove it and see if it is blocking vacuum.