EI06060 - Hydraulic Brake Booster Master Cylinder Diagnostics - Hydra Max System

This bulletin is being revised to update step 5 in the I/P MIL Light and Buzzer section. Please discard Corporate Bulletin Number 06-05-22-005 (Section 05 -- Brakes).

Important: If the customer did not bring their vehicle in for this issue, DO NOT proceed with this bulletin.

The customer may comment on any of the following items:

DO NOT REPLACE THE BOOSTER ASSEMBLY.

GM Engineering is attempting to determine the root cause of brake booster repairs. Engineering has a need to gather information on vehicles, prior to repair, that may exhibit any of these conditions. If the vehicle exhibits any of these conditions, please document the following information on the repair order:

Leakage:

If the customer's concern relates to leaks:

1. Visually inspect the following components for any signs of leaks. Note the location of any leaks:

•	Master cylinder/booster assembly

•	Power steering and booster lines

•	Power steering reservoir

•	Brake lines

2. On any component where a leak was noted, use the following cleaning process:

•	Thoroughly clean the entire area.

•	Dry completely.

3. Start the engine and apply the brakes several times, with normal foot pedal force.
4. Inspect the point of where the leak was observed. Is there any fluid present?

-	YES -- proceed to step 5.

-	NO -- 100% of the booster assemblies are tested at the supplier. Residual fluid will be present on the booster assembly from testing. The component should be considered to have no trouble found and no further diagnosis/repair is required.

5. If the leak is still present, spray the leak with water only.
6. Did the fluid dissolve in the water?

-	Yes -- this indicates the leak is brake fluid. Diagnose and repair the brake system according to SI.

-	No -- This indicates the leak is power steering fluid. Diagnose and repair the leak according to SI.

I/P MIL Light and Buzzer:

If the customer's concern relates to an MIL light and Buzzer condition:

1. Is the customer's concern present (MIL and buzzer are on)?
2. Note any DTCs current or stored in history?
3. How many miles are on the vehicle?
4. Visually inspect the master cylinder fluid level. Is the brake fluid level less than 1/2 full?

-	Yes -- fill the master cylinder reservoir using specified brake fluid. No further repair is required.

-	No -- Proceed to step 5.

5. Disconnect the electrical connector from the fluid level indicator switch located in the side of the master cylinder reservoir. Do the MIL and buzzer remain on?

-	Yes --determine if there is power to the motor, if the flow switch is open or the motor is not grounded (refer to SI diagnostics for DTC C0272).

-	No -- replace the fluid level indicator switch. No further repair is necessary.

6. With the key ON and the engine OFF, verify voltage to the backup pump. With the ignition ON, depress the brake pedal. Do you hear the backup pump run?

-	Yes -- replace the EBCM.

-	No -- determine if there is power to the motor, if the flow switch is open or the motor is not grounded (refer to diagnostics for DTC C0272).

Backup Pump Concerns:

The backup pump will only run if the flow switch is closed. The flow switch closes when no power steering fluid flows through the booster (engine not running) and the brake pedal is applied.

1. With the key ON and the engine OFF, does the backup pump run when the brake pedal is applied?

-	Yes -- the flow switch is closed. Proceed with step 3.

-	No -- proceed with step 2.

2. Disconnect the electrical connector from the backup pump. With the brake pedal applied, test for 12 volts at the connector. Is there voltage?

-	Yes -- Replace the flow control switch. No further repair is necessary.

-	No -- Check for electrical continuity from the positive terminal of the flow switch connector to the negative terminal of the flow switch connector. If no continuity, go to step 5.

3. Are the brake lights on continuously (with ignition OFF)?

-	Yes -- the brake light switch and flow switch are both closed.

-	No -- the pump relay is stuck in the closed position. Replace the backup pump -- no further repair is necessary.

4. If the backup pump runs while the engine is running and the brake pedal is applied, this may be caused by a stuck flow switch. Removing the connector from the flow switch will stop the motor from running.
5. If there is no voltage at the backup pump connector when the brake is applied, with key ON and engine OFF:

5.1.	Disconnect the electrical connector from the relay.

5.2.	Probe the Red wire to the relay. Is there 12 volts?

-	Yes -- proceed to step 5.3.

-	No -- repair wiring harness open between the relay and battery and retest to confirm 12 volts. No further repairs required.

5.3.	Disconnect the electrical connector from the flow switch.

5.4.	With brakes applied, probe the blue wire. Is there 12 volts?

-	Yes -- proceed to step 5.5.

-	No -- repair wiring harness open between the flow switch and relay.

5.5.	Check for continuity of the positive terminal to the booster housing and continuity of the negative terminal to the booster housing.

5.6.	Was there continuity?

-	Yes -- replace the motor.

-	No -- replace the flow switch.

6. Contact the engineer listed below with the information from the repair order:

*This is a unique bulletin only labor operation. This labor operation and time are not published in the Labor Time Guide.