Which of the following commercial vehicles must be equipped with an auxiliary brake?

1. Commercial vehicles with an all up weight exceeding 4,000 kg.
2. Commercial vehicles with an all up weight exceeding 6,000 kg.
3. Commercial vehicles with an all up weight exceeding 5,000 kg.
4. Correct answer: Diesel-engine vehicles with an all up weight exceeding 8,000 kg.

WhyAn auxiliary engine brake is required on diesel vehicles with an all-up weight over 8,000 kg.