What should the differential pressure reading be to prepare for towing?

• A. Zero
• B. Positive
• C. Negative
• D. High

Answer: (A)

Zero differential pressure means no brake pressure is being applied and the system is in a neutral state, which is exactly what you want when you’re preparing to tow. The differential pressure gauge compares pressure on two sides of the braking/hydraulic circuit; with zero, both sides are equal and there’s no net brake force resisting movement. That allows the tow tractor to move freely without drag or uneven braking.

If the reading were positive or negative, that would indicate some brake pressure on one side or an imbalance, causing partial braking or drag and making towing unsafe or difficult. A high reading would indicate significant brake pressure, which would also resist or complicate towing. So, zero is the correct target to confirm the system is fully released before tow.