What is this???

[zach1990]

I'll try to get better pictures when I get a chance

[Duelin]

Supplemental Brake Assist Pump Motor. A backup in case your vacuum source becomes low.

[Jsdirt]

Wonder why a gas job would have that ... unless it's got a lumpy cam?

[Duelin]

Safety!

 

Like the description say in case of loss of vacuum or low vacuum. And if I understand it correctly it will kick in if the engine quits running or engine off. And I assume that is so you still have power assist.

 

Supplemental Brake Assist

The Supplemental Brake Assist (SBA) unit creates vacuum for the brake booster in case of a vacuum loss or low vacuum to the brake booster. The SBA consists of

• The sensor circuit board and pressure sensor
• The check valve manifold
• The vacuum pump
• The motor

When the vehicle is keyed ON, the SBA performs a self test by toggling the Supplemental Brake Assist Signal Circuit low for one second. The instrument panel cluster (IPC) recognizes this as an indication that the SBA is functional. If the IPC does not see this signal for five consecutive ignition cycles the Service Brake Booster Message is displayed. The SBA performs diagnostics at 16 Km/h (10 mph) under normal conditions, and before 16 Km/h (10 mph) if a low vacuum condition exists. The SBA then spins the motor and runs diagnostics to determine if the pump is operating and the SBA is functional. The SERVICE BRAKE BOOSTER message will display until the next ignition cycle if the unit is unable to maintain reduced power brake levels.

The SBA unit utilizes the ignition on signal from the generator to determine the engine is running and monitors speed using an input from the vehicle speed sensor. It also has an internal pressure sensor that compares the pressure inside the booster to the ambient pressure. If the vacuum drops below 18 cm/Hg (7 in/Hg) the REDUCED BRAKE POWER message is displayed and a 5 second timer is started. If the vacuum stays below 18 cm/Hg (7 in/Hg) for 5 seconds the SBA starts the pump. If the vacuum drops below 15 cm/Hg (6 in/Hg) the pump comes on immediately. Once the vacuum level increases to 23 cm/Hg (9 in/Hg) The pump shuts off. The REDUCED BRAKE POWER message continues to be displayed until the vacuum level reaches 25 cm/Hg (10 in/Hg). If the pump runs for one minute without the vacuum reaching 23 cm/Hg (9 in/Hg) the pump shuts off and the SERVICE BRAKE BOOSTER message is displayed.

The SBA assembly operates in two modes.

• Low Vacuum Mode -- The low vacuum mode can occur with the engine ON or OFF. The SBA determines the ON/OFF status by monitoring the regulator output on the engine ON circuit. This mode involves SBA pump activation and deactivation due to changes in vacuum detected by the pressure sensor.
- Low Vacuum Engine ON Mode -- The SBA will operate in reaction to changes to brake booster vacuum as monitored by the pressure sensor. This mode is normally active on power up if a valid engine ON signal is detected and a low vacuum condition is indicated for more than 5 seconds.
- Reduced Brake Power Mode -- When the booster vacuum drops below 18 cm/Hg (7 in/Hg) the SBA will start a 5 second timer. If the vacuum exceeds 18 cm/Hg (7 in/Hg) the timer stops and resets. After 5 seconds the pump activates and the REDUCED BRAKE POWER message is displayed.
- Immediate Pump Activation Mode -- When the booster vacuum drops below 15 cm/Hg (6 in/Hg) the REDUCED BRAKE POWER message is displayed and the pump is turned on.
- Pump Deactivation Mode -- The pump will be turned off when the booster vacuum exceeds 23 cm/Hg (9 in/Hg). The SBA will continue to display REDUCED BRAKE POWER until the booster vacuum exceeds 25 cm/Hg (10 in/Hg).
- Low Vacuum Engine Off -- The SBA will monitor the vacuum when the vehicle is above 8 Km/h (5 mph) and an engine OFF condition is detected. If the vehicle is below 8 Km/h (5 mph) and an engine OFF condition is detected the SBA will monitor the vacuum for 60 seconds
• Vacuum Augment (Engine OFF) Mode -- If the engine ON state changes to OFF after reaching 8 Km/h (5 mph) the SBA activates the pump for up to 60 seconds. After 60 seconds the pump shuts off and the SERVICE BRAKE BOOSTER message is displayed. If the engine ON signal is detected or the vehicle slows to below 8 Km/h (5 mph) before the pump times out. The pump shuts off and no message is displayed.

[zach1990]

That's a bunch of info! Thanks! Nice to know I have that. My 2000 sierra died a couple times driving on me and I all but lost braking power in it when it did. Nice to have a backup now

[Doug_Scott]

Wonder why they dropped this. I can't see it on my 2010 Sierra. If they had of been installing this on all those cars that suffered the ignition being turned off at highway speeds, the drivers would still have had power brakes(they still had brakes as it was, it just took two feet to apply them) provided the engineers considered ignition off happening at speeds over 8mph..

[Jsdirt]

Safety!

 

Like the description say in case of loss of vacuum or low vacuum. And if I understand it correctly it will kick in if the engine quits running or engine off. And I assume that is so you still have power assist.

..........

Ahh ... good idea, given GM's track record on electronics & wiring these days. Engine dying while underway is a given.