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Why does " service brake booster" light always on??

2003 Chevy 2500 light service brake booster always on we put in new hydra boost part light still on ??

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Refer to Brake Warning System Description and Operation in Hydraulic Brakes

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
Schematic Reference: Brake Warning System Schematics
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
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
Perform the Brake Assist System Diagnosis
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 11
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
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
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
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
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
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
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
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
Start the engine.
Does the Service Brake Booster message stay on?
Go to Step 2
System OK

Posted on Dec 25, 2016


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Hello..I'm not sure what you mean when you say
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If you have power brakes with a brake booster, vacuum decreases in the power booster as the throttle opens. If you have a hydra boost system, the power steering pump provides the power assist. All system components (master cylinder, power steering pump or booster, power brakes proportioning valve, lines and fittings, calipers and pads and emergency brake) all need to be in good condition with no leakage or out of spec adjustments... to perform properly.

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Hello Patricia,

Have you checked the master brake cylinder reservoir for brake fluid loss?

I don't suspect the master cylinder as you have replaced it... but am more suspect of a leaking brake line or fitting which should have
been discovered when you had the system bled.

The only time I ever had a rear brake problem with a 2500 series Chevrolet was due to seized rear brake caliper guide your calipers are also new that is not your problem.

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