GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 1999 🢒 S/T Isuzu - 4WD 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Hydraulic Brake Diagnostic System Check

Step

Action

Normal Result(s)

Abnormal Result(s)*

1

Inspect the master cylinder fluid level.

The master cylinder fluid level is between MIN and MAX.

The master cylinder fluid level is low or high. Refer to Master Cylinder Reservoir Filling .

2
  1. Turn the ignition switch to the OFF position.
  2. Ensure that the park brake is not applied.
  3. Start the engine.

The brake warning indicator illuminates briefly (approximately 5 seconds).

3
  1. Turn the ignition switch to the RUN position.
  2. Allow the bulb test to perform.
  3. Set the parking brake.
  4. Release the parking brake.

The brake warning indicator remains ON only when the parking brake is set.

4

Hydraulic brake system pressure is low in the front or rear brake system.

The brake warning indicator illuminates.

Brake Warning Indicator Inoperative

5

With the vehicle in PARK, perform the Brake Pedal Travel Test. Refer to Brake Pedal Travel .
    • The brake pedal moves steadily toward the floor, approximately 2-3 in.
    • The brake pedal stops and is firm against the pressure. The hydraulic brake booster may hiss or clunk/click/clatter with high brake pedal effort.

6

Release the brake pedal.

The brake pedal returns to normal height.

Brake Pedal Slow Return

7
  1. Turn the engine OFF.
  2. Pump the brake pedal in order to exhaust the vacuum. Pump the brake pedal until the pedal is high and firm.
  3. While maintaining pressure on the brake pedal, start the engine.

The brake pedal falls away and then pushes back.

The brake pedal stays high and firm. Refer to Vacuum Booster Diagnosis - Hard Pedal .

8
  1. Press the brake pedal.
  2. Shift the vehicle into DRIVE.
  3. Perform the Brake System Test. Refer to Brake System Testing .
    • The braking action starts after applying the brakes.
    • The brakes do not grab and the brake pedal does not vibrate.
    • The vehicle stops without excessive pedal effort.
    • The vehicle stops without pulling to one side.
    • The front brakes and the rear brakes apply evenly.
    • The vehicle stops without noise emanating from the brakes.
    • The vehicle stops without noise emanating from the hydraulic booster.
    • The brakes do not drag after releasing the brake pedal.
    • The brakes do not make noise while driving.
    • The brakes do not pulsate.
    •  Brakes Drag
    •  Brake Pulsation

* Refer to the appropriate symptom diagnostic table for the applicable abnormal result.