In testing a parking brake, what condition is incorrect?

The condition that states the parking brake should be checked with the engine off is incorrect because testing the parking brake requires some level of engine operation to simulate the normal conditions under which the vehicle would be used.

For an accurate assessment of the parking brake's effectiveness, the vehicle needs to be in a controlled state where the brakes can engage and hold the vehicle in place under load. This is often accomplished with the engine running, allowing for increased RPM to assess whether the parking brake can maintain the vehicle's position even under added stress.

In this context, the other conditions—having the parking in neutral, being in gear in low range, or increasing the engine RPM to double idle—are essential for a proper evaluation of the parking brake's functionality, as they all contribute to ensuring the brake functions effectively under both static and active conditions.