How should you test your vehicle's low air pressure warning signal?
- Repeatedly press and release the brake pedal to lower the air pressure to 207 kPa (30 psi).
- Manually let the air out of your brakes and see if the signal comes on.
- Pump the brakes while your ignition is off.
- Repeatedly press and release the brake pedal to lower the air pressure to 380 kPa (55 psi). ✓
Answer: D. Repeatedly press and release the brake pedal to lower the air pressure to 380 kPa (55 psi).
Use the brake pedal: repeatedly press and release it to lower air pressure to 380 kPa (55 psi) and watch for the low air-pressure warning signal.
Why this is the answer
The handbook says to start with system pressure above 621 kPa (90 psi) and the ignition on, then press and release the brake pedal repeatedly to bring pressure down. Watch and listen for the warning. The test passes if the device activates at or above 380 kPa (55 psi) on both the primary and secondary gauges. That is why this method lowers pressure to the 380 kPa (55 psi) test point and checks the signal there.
Why the other answers are wrong
- A. Repeatedly press and release the brake pedal to lower the air pressure to 207 kPa (30 psi). — Lowering the pressure all the way to 207 kPa (30 psi) goes past the handbook's 380 kPa (55 psi) test point and does not describe the specified warning-signal check.
- B. Manually let the air out of your brakes and see if the signal comes on. — The handbook tells you to reduce pressure by pressing and releasing the brake pedal, not by manually letting air out of the brakes.
- C. Pump the brakes while your ignition is off. — Pumping the brakes with the ignition off will not work because the handbook requires the ignition to be on for the warning device to activate.
Remember it
Think 55 psi: ignition on, pump the pedal, and expect the warning at or above 380 kPa.