Is it necessary to turn off the engine when performing your air brake leak-down test?

Turning off the engine when performing your air brake leak-down test is necessary for several reasons. First, the purpose of the leak-down test is to check for air leaks in the system while it is at rest, as the engine running would affect the air pressure and potentially mask any leak issues. By shutting off the engine, you ensure that the air supply is stabilized, allowing for an accurate assessment of the air pressure loss in the brake system.

Furthermore, performing this test with the engine off minimizes safety risks, as the vehicle is not in operation, reducing the chance of unintended movement or noise interference that might distract from the test results. This ensures that the driver can focus solely on the air brake system's integrity without the added complexity of engine operations.

In summary, turning off the engine guarantees a precise measurement of any air loss, which is critical for maintaining the safety and effectiveness of the braking system.