A trailer’s spring brakes must automatically apply whenever the trailer is disconnected from the towing vehicle. To test this, open (push in) the trailer supply valve to fully charge the trailer. Then pull out the trailer supply valve to close it. The trailer spring brakes should apply. Disconnecting the trailer air supply line also activates this function, but closing the trailer supply valve is the recommended testing method. Brake application may be confirmed by gently applying engine power to move the vehicle forward or backward.

If the trailer spring brakes fail to apply automatically when the trailer supply valve is closed, the trailer brakes are defective.

Step-by-step procedure

1. Ensure the trailer supply valve is open (pushed in) and the trailer is fully charged.
2. Ensure the air brake system is within its normal operating pressure range.
3. Pull out the trailer supply valve to close it.
4. Observe the trailer for application of the trailer’s spring brakes.
5. If necessary, confirm brake application by attempting to gently move the vehicle forward or backward.

Pass

The vehicle passes the test if the trailer spring brakes apply automatically.

Fail

The vehicle fails the test if the trailer spring brakes do not apply.

Important: The Ontario Highway Traffic Act and regulations prohibit the operation of a vehicle with defective trailer spring brakes.