LGV Coupling and Uncoupling

Question 1

What is the first thing a driver should check before coupling a tractor unit to a semi-trailer?

Accepted Answer

That the trailer is on a firm, level surface with the parking brake applied and the landing gear supports it

Answer

Before coupling, ensure the trailer is on firm, level ground, the parking brake is applied, and the landing gear (legs) is properly supporting the trailer at the correct height for the 5th wheel to engage beneath the trailer plate.

Question 2

After the 5th wheel has engaged with the trailer kingpin, what test must the driver perform?

Accepted Answer

A pull test (tug test) — gently try to pull away with the trailer brakes applied to confirm the coupling is locked

Answer

The driver must perform a pull test by applying the trailer brakes and gently attempting to drive forward. If the coupling is properly locked, the tractor will not separate from the trailer. This confirms the jaws are fully closed around the kingpin.

Question 3

In what order should the air lines (susies) be connected when coupling?

Accepted Answer

It does not matter which order

Answer

Modern best practice is to connect both lines ensuring the correct line goes to the correct coupling head — red to red (emergency) and yellow to yellow (service). The key is correct colour matching rather than sequence, though some operators specify emergency first.

Question 4

What should a driver visually check on the 5th wheel after coupling?

Accepted Answer

That the locking jaws are closed around the kingpin, the release handle is in the locked position, and there are no gaps

Answer

The driver must visually check that the locking jaws are fully closed around the kingpin (no visible gap between the trailer plate and the 5th wheel), the release handle is in the locked position, and any safety catch is engaged.

Question 5

When must the trailer landing gear (legs) be fully raised after coupling?

Accepted Answer

After confirming the coupling is secure and before driving away

Answer

The landing gear must be fully raised and secured after the coupling has been confirmed as secure. Driving with the landing gear down can cause serious damage if they contact the road surface, particularly on uneven ground or speed bumps.

DVSA UK Driving Theory Practice Test

DVSA UK Driving Theory Practice Test

LGV Coupling and Uncoupling