How to test my brake booster to find out if it is working properly or not. Thanks

SERVICE BRAKE BOOSTER
Refer to Brake Warning System Description and Operation in Hydraulic Brakes

SERVICE BRAKE BOOSTER
The SERVICE BRAKE BOOSTER message will be displayed when the supplemental brake assist signal circuit is toggled at 1.0 Hz with a 50 percent duty cycle. This message is also displayed if the instrument panel cluster (IPC) does not see an alive and well signal at key on. When this message is displayed it indicates a problem with the SBA and should be serviced or replaced.

How do the power brakes work ? Good .?

Service Brake Booster Message Displayed
Step
Action
Yes
No
Schematic Reference: Brake Warning System Schematics
1
Did you review the Brake Warning System Description and Operation and the Brake Assist System Description and Operation and perform the necessary inspections?
YES - Go to Step 2
NO - Go to Symptoms - Hydraulic Brakes
2
Start the vehicle.
Is the REDUCED BRAKE POWER message displayed for 1 minute before the SERVICE BRAKE BOOSTER message is displayed?
YES - Go to Step 3
NO - Go to Step 4
3
Perform the Brake Assist System Diagnosis
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 11
4
Disconnect the Supplemental Brake Assist connector.
Test the ignition 1 circuit for an open or a short to ground.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 5
5
Test both ground circuits for opens.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 6
6
Test the engine on signal circuit for an open or a short to ground.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 7
7
Test the vehicle speed signal circuit for an open.
Did you find and correct the condittion?
YES - Go to Step 12
NO - Go to Step 8
8
Test the supplemental brake assist signal circuit for an open or a short to voltage.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 9
9
Connect the supplement brake assist connector.
Disconnect the instrument panel cluster connector.
Connect a DMM from battery positive voltage to the supplemental brake assist signal circuit.
Turn the ignition to the RUN position while observing the DMM.
Did the DMM flash battery voltage?
YES - Go to Step 11
NO - Go to Step 10
10
Replace the Supplemental Brake Assist pump motor assembly Refer to Power Brake Booster Auxiliary Pump Replacement .
Did you complete the replacement?
YES - Go to Step 12
--
11
Replace the instrument panel cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.
Did you complete the replacement?
YES - Go to Step 12
--
12
Start the engine.
Does the Service Brake Booster message stay on?
Go to Step 2
System OK

you test a brake booster with vacuum not air pressure
the vacuum check valve is at the end of the vacuum hose in the booster
Don't mess with it --just get a good unit from the wreckers / junk yards or a reconditioned unit from an accredited brake shop

With the engine off, depress the brake pedal about 6 times, all the way up and down. While holding the hard pedal down, start the engine, and if the booster is working properly, the pedal will fade down a little bit.

Simple test for brake power booster... pump brake pedal two or three times,while holding brake pedal down start the vehicle up.The brake pedal should drop if the booster is working properly :)

If the pads are being applied and you are not pushing on the pedal, it could be something going on with the ABS.

Not sure if you have done all this.



BRAKE BOOSTER INSPECTION

Functional test:
1. With the engine stopped, Depress the brake pedal several times, then depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line or a brake caliper is faulty
2. Start the engine with the pedal depressed. If the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or the check valve is faulty

Leak Test:
1. Depress the brake pedal with the engine running then stop the engine. If the pedal height does not vary while depressed for 30 seconds, the vacuum booster is OK. If the pedal rises, the booster is faulty
2. With the engine stopped, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.

Check valve test:
1. Disconnect the brake booster vacuum hose at the booster.
2. Start the engine and let it idle. There should be a vacuum available. If no vacuum is available, the check valve is not working correctly. Replace the check valve and retest.

END TEST

skdavisbob, This sounds like you have a problem with the brake booster that is attached to the firewall. When these boosters fail it is like trying to stop a house as you describe here. There is a one way check valve near the top of the booster that uses vacuum from the engine to operate. Inspect the hose and be sure that it is attached at both ends and that there are no leaks in this hose. This can be done by running the engine and listening for a leak. (hissing noise) Replace the hose if faulty. If you don't hear any vacuum leak then turn the engine off and pull the check valve out of the booster. This takes a little effort as it is quite secure in the grommet. You should hear a vacuum leak for a split second because when the valve is removed it will allow air in (if it is working properly) and you should hear the leak. If you don't hear the hiss, then test the valve by blowing through it both ways. As stated, this is a one way valve and you should be able to blow air through one way but not the other. If you can blow air both ways then the check valve is faulty. If the hose and valve are working properly then you will have to have the booster replaced. Good luck with this.

the booster is the problem, or a hole or leak in vacuum line to booster check the check valve also ! from manifold. heres the symtoms of a bad brake booster. primary symtom is a hard pedal on application, to test booster. pump brakes several times with engine off. to deplete stored vacuum. turn on engine with pushing slightly on brake pedal. you should feel the pedal fade away abit and then become firm. but not hard. if you feel nothing at pedal when engine starts, brake booster is not working! check the vacuum lines first!!

Check another vac source in/around engine. When you load engine with brake booster, then lower vac pressure w/Up idle, it's amplifying another vac source that might be weak.

Check the vacuum supply line to the brake vacuum booster. Make sure the line is properly attached to the engine and has no leaks. If ok, then you likely have a bad booster.

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