Study guide
8.3 Trip Air Brake Inspection Steps 1–3: Tractor Protection and Park Control Checks
Alberta Air Brake Q Endorsement
Track your progress as you read
Finished sections get a check mark.
1 Chapter 1: Alberta Q Endorsement Program and Air Brake Fundamentals
1.1 Alberta Q Endorsement Path, Course Requirements, and Knowledge Test Logistics 1.2 Licensing Scope, Farm Vehicle Exceptions, and the Technician Route 1.3 Air Brake System Fundamentals: Compressed Air, Pressure Units, Safety, and Schematic Colours
2 Chapter 2: The Supply Circuit: Compressor, Governor, Tanks, and Air Dryers
2.1 Air Compressors, Drive Systems, and Governor Operation 2.2 Supply and Service Tanks, Contamination, and Draining 2.3 Air Dryers, Air Brake Antifreeze, Safety Valves, and Check Valves
3 Chapter 3: Service Circuits, Control Valves, Gauges, and Low-Air Warnings
3.1 Dual Air Systems: Primary and Secondary Service Circuits 3.2 Brake Chambers, Control Valves, Quick Release Valves, and Relay Valves 3.3 Air Pressure Gauges, Low-Air Warnings, and the Driver's Response
4 Chapter 4: The Park Circuit and Tractor/Trailer Circuits
4.1 Spring Parking Brakes, the Park Control Valve, Compounding, and Caging 4.2 The Tractor Protection System, Trailer Supply Valve, and Glad Hands 4.3 Trailer Service Control, the Trailer Hand Valve, and Air Park Brake Trailers
5 Chapter 5: Air System Failures and Emergency Braking
5.1 Tractor Air System Failures: Supply, Primary, Secondary, and Park Circuits 5.2 Trailer Air System Failures: Service Line, Supply Line, Reversed Lines, and Trailer Tanks
6 Chapter 6: Foundation Brakes and Brake Adjustment
6.1 Foundation Brakes: S-Cam Drum, Disc, and Wedge Brakes 6.2 Brake Stroke, Adjustment Limits, and Stroke Indicators 6.3 Adjusting Manual Slack Adjusters and Maintaining Automatic Slack Adjusters
7 Chapter 7: Braking Fundamentals, Driving Techniques, and Brake Management Systems
7.1 Braking Fundamentals: Heat, Brake Lag, Stopping Distance, and Fade 7.2 Downgrades, Auxiliary Retarders, Bobtailing, and Winter Braking 7.3 Antilock Brakes, Automatic Traction Control, and Stability Control
8 Chapter 8: Vehicle Inspections and the Air Brake Practical Test
8.1 Trip Inspection Law, Major and Minor Defects, and Roadside Enforcement 8.2 Inspection Set-Up and Recognizing Air Brake Defects 8.3 Trip Air Brake Inspection Steps 1–3: Tractor Protection and Park Control Checks 8.4 Trip Air Brake Inspection Steps 4–6: Supply Circuit, Leak Test, Brake Adjustment, and Scoring
8.3 Trip Air Brake Inspection Steps 1–3: Tractor Protection and Park Control Checks
Key Takeaways Explain This Topic AI
The inspection starts with full tanks, cycles the pressure down with the tractor protection check, builds it back up with the supply circuit check, and then tests for leaks with the system full again.
Step 2 set-up: engine off with the key in the run position, red trailer air supply valve pushed in, yellow park control pulled out, and both air lines to the trailer disconnected.
In Step 2, the red valve should pop out at 40–60 PSI (276–414 kPa) or higher and the low-air warning should come on by 60 PSI; then apply and hold the foot or hand valve, and no air should leak from the open service line.
Step 3: push in the yellow park control, pump the foot valve, and confirm it pops out at 20–45 PSI (138–311 kPa); then reconnect both air lines.
Each of these eight checks is worth 5% on the Air Brake Practical Test form, so together they are worth 40% of the practical score.
Last updated: September 2026
Trip Air Brake Inspection Steps 1–3: Tractor Protection and Park Control Checks
Quick Answer: Alberta's trip air brake inspection has six steps , set out in the Commercial Driver's Guide and the Air Brake Practical Test form. It starts with full tanks . Step 1: chock the wheels and inspect the components visually. Step 2 (tractor protection): turn the key to run with the engine off, push the red button in and pull the yellow button out, then disconnect both trailer lines . The red button must pop out at 40–60 PSI or higher , and the low-air warning must come on by 60 PSI . Then apply and hold the brakes: no air should leak from the open service line . Step 3 (park control): push the yellow button in and pump the pedal; it must pop out at 20–45 PSI . Then reconnect both lines .
Why the steps come in this order
The instructor manual explains the logic of the sequence:
Start with the air tanks full.
Cycle the pressure down with the tractor protection system check (Step 2), and keep lowering it with the park control check (Step 3).
Build it back up with the supply circuit check (Step 4), which needs low pressure to start the build-up test.
Test for leaks with the system full again (Step 5).
Each step sets up the next. Doing them out of order wastes time you do not have on a 15-minute practical test.
Step 1: Set-up and visual inspection
Chock the wheels with the vehicle on level ground .
Visually inspect the air brake components (Section 8.2).
Step 2: Tractor protection system
Action What you should see Why
Leave the engine off with the key in the run position Gauges and warnings powered The compressor must not refill the tanks during the check
Push the red trailer air supply valve in; the yellow park control should be pulled out Trailer charged; tractor spring brakes applied The yellow button holds the unit on its springs, and the red button charges the supply line
Disconnect both air lines to the trailer Air escapes from the open supply coupler, and tractor pressure falls Simulates a breakaway
Watch the red button It should pop out at 40–60 PSI (276–414 kPa) or higher Proves the trailer supply valve protects the tractor's air
Watch the low-air warning It should come on by 60 PSI (414 kPa) This can also be checked in the supply circuit section
Apply and hold the foot valve or the hand valve No air leaks from the open trailer service line Proves the tractor protection valve has closed the service line
How to disconnect a live line. Place your hand between the glad hand couplers and your face so the escaping air cannot blow debris into your face, and wear appropriate PPE.
If the red button trips at once. On some vehicles, the trailer supply valve trips immediately after the lines are separated. In that case, return to the cab and firmly apply the foot valve to confirm that the tractor protection valve has closed the trailer service line.
The same check at roadside. In a Level 1 CVSA inspection, officers remove both lines, wait for the red button to trip, and ask the driver to apply the service brake. The service line must not leak. A tractor protection system that fails puts the vehicle out of service .
Step 3: Park control valve
The park control valve is not part of the tractor protection system , but it is efficient to check it here while the pressure is already coming down.
- Action What you should see
- Push the yellow park control valve in Air goes to the spring brakes
- Pump the foot valve Pressure drops further
- Watch the yellow button It should pop out at 20–45 PSI (138–311 kPa)
Reconnect both air lines to the trailer Inspect the glad hands before connecting, connect them properly, confirm the connection, and check that the lines are suspended so they will not catch as the trailer turns
Notes from the course:
The low-air warning can also be confirmed here: with the yellow button pushed in, reduce pressure until it pops out.
The yellow button sometimes pops out below 20 PSI, even on new vehicles . Make sure it pops out to its default park position before the tanks are empty . A park control that does not default to park when the air is depleted puts the vehicle out of service .
How Steps 1–3 are scored on the practical test
On the Air Brake Practical Test form, each of these items carries 5% :
- Section Item on the form Weight
- Tractor protection Push the red button; the yellow should be pulled 5%
- Tractor protection Disconnect both air lines to the trailer 5%
- Tractor protection Confirm the low-air warning comes on by 60 PSI (414 kPa) 5%
- Tractor protection Confirm the red button pops out at 40–60 PSI (276–414 kPa) or higher 5%
- Tractor protection Apply and hold the foot or hand valve; no air leaks from the open service line 5%
- Park control valve Push the yellow button and pump the foot valve 5%
- Park control valve Confirm the yellow button pops out at 20–45 PSI (138–311 kPa) 5%
- Park control valve Reconnect both air lines to the trailer 5%
These eight items total 40% of the form. Because 25% or more in errors fails the test, missing five of them would fail you on its own.