Diagnostics - Vacuum System Leak Test

If any leaks are detected, replace the vacuum hose assembly.

Both of the procedures below should be performed in combination as part of any diagnostic for a brake vacuum system performance fault. The procedures should also be performed after any repairs are made to verify the system is not leaking. A leaky system can cause premature electric vacuum pump failure due to over operating the pump.

CHECK THE VACUUM HOSE ASSEMBLY FOR A LEAK: 

Steps 1 and 2 require the vacuum hose assembly to be disconnected from the booster, engine, and Electric Vacuum Pump (EVP). If the sensor is not part of the vacuum hose assembly, remove the sensor from the booster and leave connected to the vacuum hose assembly. Once fully disconnected, the sensor must be plugged as to not allow leakage through the internal check valve. Plug method should be clean to prevent contamination into the sensor check valve.

1. Connect a hand vacuum pump to the EVP connection (6) and pull a vacuum of 8.0 kPa (23.5 In.Hg). Once vacuum is pulled to the correct level, measure vacuum loss over one minute. This will check for leakage in the engine check valve and all the vacuum hose assembly inside the green dashed line (4). The vacuum hose assembly should not leak more than 4.5 kPa (1.3 In.Hg) in one minute.
2. Next connect to the engine connection (3) and pull a vacuum of 8.0 kPa (23.5 In.Hg). Once vacuum is pulled to the correct level, measure vacuum loss over one minute. This will check for leakage in the EVP connection check valve and all the vacuum hose inside the orange dashed line (5). The vacuum hose assembly should not leak more than 4.5 kPa (1.3 In.Hg) in one minute.
3. Last, remove the plug from the sensor and pull a vacuum directly on the sensor (2) where it would be installed into the booster. Pull a vacuum of 8.0 kPa (23.5 In.Hg). Once vacuum is pulled to the correct level, measure vacuum loss over one minute. This will check leakage in the sensor check valve (2). The sensor check valve should not leak more than 4.5 kPa (1.3 In.Hg) in one minute.
   • If any of the above checks fail, the vacuum hose assembly should be replaced as an assembly. The check valves cannot be replaced separately.
   • If the above vacuum checks pass, continue to CHECKING THE BRAKE BOOSTER SIDE FOR A LEAK.

Courtesy of CHRYSLER GROUP, LLC

CHECKING THE BRAKE BOOSTER SIDE FOR A LEAK:  This procedure checks the brake booster for leakage. Securely install the vacuum hose assembly on the vehicle.

1. Turn the ignition on and monitor the brake pressure sensor data with the scan tool. NOTE: The value is multiplied by (-1) so that the reading shows as a positive value. The value displayed in the scan tool may need to be converted to metric. 
2. Start and run the engine for at least 30 seconds while monitoring the brake pressure sensor data on the scan tool. Allow the value to stabilize, then immediately cycle the ignition off and back to ignition on engine not running. Monitor and record the pressure loss for the initial 15 seconds (the pressure should not drop more than 2.0 kPa (0.60 In.Hg) in the first 15 seconds). Monitor and record the pressure loss after an additional 45 seconds (the pressure should not drop more than 2.5 kPa (0.75 In.Hg) over the next 45 seconds).
   1. If the pressure drop was less than the thresholds listed above the brake booster and vacuum pressure sensor check valve are operating normally. If the P258B fault is present, perform the VACUUM PUMP  diagnostic.
   2. If the pressure drop was more than the thresholds listed above there is a leak at the brake booster. Replace the brake booster and retest.