Possible Causes

Vacuum hoses
Front hublock IWE vacuum hose connection
Brake master cylinder seal
Vacuum tube grommet
Vacuum sensor grommet

CB1: CHECK FOR OTHER ABS MODULE DTCS

Ignition ON, engine OFF.
Carry out the ABS self-test.
Carry out the PCM KOEO self-test.

Is DTC C101A:15, C101A:16, C101A:1C or C101A:29 present?

Yes	No
Go to PINPOINT TEST CA .	Go to CB2.

CB2: CHECK THE BRAKE BOOSTER AND VACUUM COMPONENTS

Ignition OFF.
Inspect the following components for signs of obvious damage:
- Vacuum tube grommet
- Vacuum sensor grommet
- Brake master cylinder seal
- Vacuum hoses and tubes
- Brake booster
- Front hublock IWE vacuum hose connection

Are the components listed free from any damage?

Yes	No
Go to CB3.	INSTALL new components as necessary. Go to CB3.

CB3: TEST THE BRAKE BOOSTER

Carry out the Component Test - Brake Booster.
- Refer to Brake System - General Information (Hybrid/Energi) .

Was the component test successful?

Yes	No
Go to CB4.	INSTALL new components as directed by the component test.

CB4: VERIFY ABS MODULE VACUUM/PRESSURE SENSOR SIGNAL 1 (VAC_PRS_S1) PID

NOTE: Running the engine with the vacuum sensor removed from the brake booster sets DTCs in the ABS module. Clear all DTCs once the repair is complete.

Start the engine and allow to idle for at least 20 seconds.
Access the ABS and monitor the VAC_PRS_S1 (PRESS) PID.
Note the PID display.
Ignition OFF.
Remove the vacuum sensor from the brake booster.
- Leave the electrical connector connected.
Connect a vacuum gauge to the vacuum sensor port.
Start the engine and allow to idle for at least 20 seconds.
Read and record the vacuum gauge display.
Ignition OFF.
Disconnect the vacuum gauge from the brake booster and install the vacuum sensor.

Does the VAC_PRS_S1 PID display match the recorded vacuum gauge display ±10 kPa (3 inches Hg)?

Yes	No
The condition causing the concern is not present at this time. The concern may be temperature related. ALLOW the vehicle to remain outside overnight and RETEST the vacuum system.	INSTALL a new Brake Booster Vacuum Sensor. REFER to Power Brake Actuation - Brake Booster (Hybrid/Energi) .