Diagnostic Technique No. 4 — Brake Pedal Reserve—Check

Where a low pedal or the feel of a bottomed out condition exists, check for brake pedal reserve.

1. Operate engine at idle with the transmission in either PARK or NEUTRAL.

2. Depress brake pedal lightly three to four times.

3. Allow 15 seconds for vacuum to replenish booster.

   NOTE: This increased resistance may feel like something has bottomed out.

4. Apply brake pedal until it stops moving downward or an increased resistance to the pedal travel occurs.

5. Hold pedal in applied position and raise the engine speed to approximately 2,000 rpm.

   NOTE: The additional movement of the brake pedal is the result of the increased engine manifold vacuum which exerts more force on the brake booster during engine rundown. This means that additional stroke is available in the master cylinder, and the brake system is not bottoming out.

6. Release accelerator pedal and observe that brake pedal moves downward as engine returns to idle speed.