Service Procedure

INSPECTION PROCEDURE

The following inspection procedure is for determining whether the vacuum brake booster is operating properly and not binding internally when the brake pedal is released. Please read the entire procedure before performing it.

IMPORTANT:
To get accurate test results, this inspection procedure must be done on a cold vehicle. A cold vehicle is defined as a vehicle that has not had the engine running for at least 4 hours or the underhood temperature is at or below 27° C (80° F). This test can be performed a second time if necessary. However, if you desire to perform the test a third time, you must allow the vehicle to become cold again.

1. Open the hood.

2. Open the driver's door and set the parking brake.

3. Connect a Tech 2 to the vehicles Data Link Connector under the Instrument Panel.

4. Turn the ignition switch to the "ON" position but do not start the engine.

5. Follow the appropriate menu screens on the Tech 2 and enter the appropriate vehicle information.

IMPORTANT:
Both engine RPM and brake switch status information are needed to perform this inspection. For vehicles without a tachometer located in the instrument panel, both the engine RPM and (TCC) brake pedal switch status can be found in "Engine Data 1" which is under "Data Display" in the "Powertrain" menu. Use the features on the Tech 2 for displaying both at the same time. For vehicles with a tachometer in the instrument panel, you can use the above method, or you can find the brake switch status information in "ABS Data" which is under "Data Display" in the "Chassis" menu on the Tech 2.

6. Follow the appropriate step based on the type of transmission in the vehicle:

^ Automatic transmissions: With the engine still off and while observing the Tech 2, pump the brake pedal hard six (6) times with your LEFT foot and then hold the pedal down firmly. Do not release the pedal until instructed to.

^ Manual transmissions: With the engine still off and while observing the Tech 2, pump the brake pedal hard six (6) times with your RIGHT foot and then hold the pedal down firmly. Do not release the pedal until instructed to. Your left foot will be used later for depressing the clutch pedal.

7. On vehicles with manual transmissions, place the gearshift in neutral and depress the clutch pedal with your LEFT foot.

IMPORTANT:
When the engine is started in the next step, the brake pedal will begin to go down. This is a normal condition. Continue to hold the pedal down firmly.

8. With your foot still firmly applied on the brake pedal, start the engine and allow it to run for ten seconds before proceeding to the next step.

IMPORTANT:
On vehicles with manual transmissions while keeping the brake pedal depressed, transfer your left foot to the brake pedal and remove your right foot.

9. Using your right foot, depress the accelerator pedal to increase the engine speed to approximately 3,000 RPM and then release the pedal and allow the engine to return to idle.

IMPORTANT:
To obtain accurate test results, you must keep observing the brake status on the Tech 2 during the next step. You will be looking to see if the brake switch status or TCC brake pedal switch changes from "applied" to "released" in less than one (1) second.

IMPORTANT:
Read the next step completely before performing it.

10. While observing the brake switch status or TCC brake pedal switch on the Tech 2, begin to slowly and smoothly release the brake pedal. The process of slowly releasing the brake switch should take about 3 seconds. When your foot is completely off the brake pedal, the brake switch status or TCC brake pedal switch on the Tech 2 should switch from "applied" to "released"

^ If the brake switch status or TCC brake pedal switch changed from "applied" to "released" in one (1) second or less from when you removed your foot from the pedal, the brake booster is good. Proceed to the last step of this procedure.

^ If the brake switch status or TCC brake pedal switch changed from "applied" to "released" more than one (1) second from when you removed your foot from the pedal, the brake booster needs to be replaced.

11. Disconnect the Tech 2.

12. If the brake booster requires replacement, see the appropriate service manual for servicing information.

13. Install the GM Identification Label and close the hood.