DTC Advanced Diagnostics: U3003-16
DTC U3003-16: Brake Booster Control Unit Power Circuit (+B) Low Voltage
NOTE
Initial Diagnosis:
The initial on-board diagnosis occurs right after the vehicle condition is turned to the ON mode, and the brake system indicator (red or amber) comes on, and continues until the indicator goes off.
Regular Diagnosis:
The regular on-board diagnosis begins right after the brake system indicator (red or amber) goes off, and it continues until the vehicle condition is turned to the OFF (LOCK) mode.
Review "How to Troubleshoot the Electric Brake Booster System" before doing the DTC troubleshooting procedure.
Test-drive the vehicle according to local traffic conditions and regulations. Do not test-drive on a lift unless specified.
The possible causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.

Confirmation Procedure
With the Driving Pattern:
1.
Turn the vehicle to the ON mode.
Execution
Initial Diagnosis/Regular Diagnosis
Duration
About 1 second
DTC Type
1 drive cycle
Brake system indicator (red) on (Dependant upon the conditions)
Brake system indicator (amber) on (Dependant upon the conditions)
Fail Safe Action
Stop servo control function (Dependant upon the conditions)
Stop automatic brake hold function (Dependant upon the conditions)
Stop ACC function (Dependant upon the conditions)*
Stop CMBS function (Dependant upon the conditions)*
Possible Cause
Open or Short to ground between the electric brake booster and the under-hood fuse/relay box (+B EBB line)
Fuse failure (Under-hood fuse/relay box No. A1-2 (40 A))
Open or Short to ground between the electric brake booster and the under-dash fuse/relay box (+B OPTION line)
Fuse failure (Under-dash fuse/relay box No. D24 (5 A))
Alternator failure
Abnormal 12 volt battery
Electric brake booster internal failure
*: With ACC