Normal Operation and Fault Conditions

The ABS module uses a sensor mounted on the brake booster to monitor the vacuum in the brake booster. When a failure in the vacuum system occurs, the ABS sets a DTC, sends a message to the IPC to illuminate the red brake warning indicator, and the force required to press the brake pedal increases. 

For engines equipped with a mechanical vacuum pump driven by the camshaft a pump failure or a leak in the vacuum hoses, check valve, seals, brake booster or front hublock (if equipped) can cause a failure in the vacuum system. 

For engines not equipped with a mechanical vacuum pump a leak in the vacuum hoses, check valve, seals, brake booster or front hublock (if equipped) can cause a failure in the vacuum system. 

1. CB1: CHECK BRAKE PEDAL FEEL 
   • Ignition ON, engine running.
   • Press and release the brake pedal at least 3 times.
   • Does the brake pedal have a hard or firm feel when pressed? 

     Yes	No
     DIAGNOSE the brake booster. REFER to Component Tests in Brake System - General Information article.	Go to  CB2.

2. CB2: CHECK FOR OTHER ABS MODULE DTCS 
   • Ignition ON, engine OFF.
   • Carry out the ABS self-test.
   • Carry out the PCM KOEO self-test.
   • Are any C101A:xx DTCs present? 

     Yes	No
     Go to PINPOINT TEST CA .	Go to  CB3.

3. CB3: CHECK THE BRAKE BOOSTER AND VACUUM COMPONENTS 
   • Ignition OFF.
   • Are the components listed free from any damage? 

     Yes	No
     Go to  CB4.	INSTALL new components as necessary. Go to  CB4.

4. CB4: TEST THE BRAKE BOOSTER 
   • Carry out the Component Test - Brake Booster.
     • Refer to Diagnosis and Testing in Brake System - General Information article.
   • Was the component test successful? 

     Yes	No
     Go to  CB5.	INSTALL new components as directed by the component test.

5. CB5: 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.
     NOTE: 100mbar = 10 kPa = 3 in Hg
   • 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 article.