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Spongy Brakes and ABS Light on 2020 CX-9 - Time for Brake Fluid Flush?

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Mike T. · rep 0 · May 25, 3:36 AM · 1 replies · solved · Question

Vehicle: 2020 Mazda CX-9 Grand Touring

Hey everyone, I'm driving a 2020 Mazda CX-9 Grand Touring with about 45,000 miles on it. Lately, I've noticed the brake pedal feels a bit spongy, and I've had the ABS warning light come on intermittently. It usually goes off after a restart, but it's concerning. I haven't had the brake fluid changed since I bought it new.

Could this be related to old brake fluid? I know brake fluid absorbs moisture over time, but I wasn't sure if that would trigger an ABS light. The brake pads are still good, and there are no obvious leaks. What's the recommended interval for a brake fluid flush on these CX-9s? Any thoughts or similar experiences?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 3:36 AM

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ClearTheCode admin answer:

Your observations of a spongy brake pedal and an intermittent ABS light on your 2020 Mazda CX-9 at 45,000 miles strongly suggest that a brake fluid flush is due and could be contributing to the issues. Brake fluid is hygroscopic, meaning it absorbs moisture from the air over time, which degrades its performance and lowers its boiling point. Mazda generally recommends a brake fluid flush every 2-3 years or 30,000-45,000 miles, whichever comes first.

Here's how old brake fluid can cause your symptoms and what to do:

  1. Spongy Pedal:

    • Cause: Moisture in the brake fluid can turn to steam under high braking temperatures. Steam is compressible, unlike fluid, leading to a soft or spongy pedal feel.
    • Action: A full brake fluid flush will replace the old, moisture-laden fluid with fresh, new fluid, restoring pedal firmness.

  2. ABS Light:

    • Cause: While directly linked to a faulty ABS sensor or module, degraded brake fluid can indirectly contribute. Moisture in the system can lead to corrosion within the ABS modulator, potentially causing intermittent faults. Additionally, low fluid levels (due to pad wear, not leaks) can also trigger the light.
    • Action: After a flush, ensure the brake fluid reservoir is at the correct level. A diagnostic scan can confirm if there are any specific ABS fault codes stored (e.g., C0020 for ABS pump motor, C0031 for wheel speed sensor).

Maintenance Steps:

  • Brake Fluid Flush: This is a critical maintenance item. Ensure a DOT3 or DOT4 fluid (check your owner's manual for the exact specification) is used. The entire system, including the ABS module, should be bled thoroughly.
  • Inspect Brake System: While flushing, have the mechanic inspect all brake lines, calipers, and wheel speed sensors for any damage or corrosion.
  • Check for Leaks: Although you mentioned no obvious leaks, a professional inspection can confirm this.

When to See a Shop:

  • Immediately for the brake fluid flush. This is a safety-critical system.
  • If the ABS light remains on after the flush and a diagnostic scan. There might be an underlying issue with an ABS sensor or the ABS module itself that needs specialized attention.
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