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Check brake system message
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<blockquote data-quote="FordTechOne" data-source="post: 1626157" data-attributes="member: 35543"><p>You have one of a few possible issues occurring - A biased brake vacuum sensor that is reading artificially low, a vacuum leak, a leaking booster check valve, or a failed booster.</p><p> </p><p>The ABS monitors vacuum at the brake booster to ensure sufficient vacuum in available for full brake assist. If the sensor reports low battery vacuum, the ABS module will run the hydraulic pump motor in the HCU to provide supplemental brake assist. This is why it feels like your ABS is activating at low speeds; it’s providing additional hydraulic pressure.</p><p></p><p>I would recommend verifying the actual vacuum available at the brake booster first. At hot idle, it should be approximately 17-20 in-hg. If it’s low, you have an engine performance issue (unlikely) or there is still a leak somewhere. Cap off vacuum lines until you find the source of the leak.</p><p></p><p>If sufficient vacuum in available, suspect a leaking booster check valve. When you accelerate, engine vacuum drops. The check valve is there to prevent vacuum in the booster from depleting. You should only be able to blow air through the check valve in one direction; otherwise is is faulty.</p></blockquote><p></p>
[QUOTE="FordTechOne, post: 1626157, member: 35543"] You have one of a few possible issues occurring - A biased brake vacuum sensor that is reading artificially low, a vacuum leak, a leaking booster check valve, or a failed booster. The ABS monitors vacuum at the brake booster to ensure sufficient vacuum in available for full brake assist. If the sensor reports low battery vacuum, the ABS module will run the hydraulic pump motor in the HCU to provide supplemental brake assist. This is why it feels like your ABS is activating at low speeds; it’s providing additional hydraulic pressure. I would recommend verifying the actual vacuum available at the brake booster first. At hot idle, it should be approximately 17-20 in-hg. If it’s low, you have an engine performance issue (unlikely) or there is still a leak somewhere. Cap off vacuum lines until you find the source of the leak. If sufficient vacuum in available, suspect a leaking booster check valve. When you accelerate, engine vacuum drops. The check valve is there to prevent vacuum in the booster from depleting. You should only be able to blow air through the check valve in one direction; otherwise is is faulty. [/QUOTE]
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