In which situation should you never rely solely on the service brakes?

Relying solely on the service brakes when driving downhill can create a dangerous situation due to the added strain and potential overheating of the braking system. When descending a hill, gravity increases the vehicle's speed, which means more brake force is needed to maintain control. To safely manage this, drivers should use a combination of service brakes and engine braking, typically achieved through downshifting to lower gears. This technique reduces the reliance on the service brakes alone, helping prevent brake fade, which can occur when brakes overheat from continuous use.

Other scenarios like approaching a red light, navigating city traffic, or preparing to park may involve braking but do not inherently require such a heavy reliance on the brakes due to external factors like incline and weight that are present when driving downhill.