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Limits of HOLD Function
The limits set by the physics of driving cannot be overcome, even with the HOLD function. Responsibility for driving off on upward slopes is still the driver's, despite the HOLD function.
Assistance by the HOLD function is not always guaranteed when stopping and driving off on a slippery surface (e.g. on icy or loose surfaces).
In this case, the vehicle can slip.
Drive-Off Assistant Not Working
If the Drive-Off Assistant is not functioning, the driver cannot be assisted when driving off on hills.
If the vehicle comes to a standstill on a steep uphill gradient without using the service brake, this may result in a certain roll-back before the vehicle is held by the HOLD function. In this situation, the driver can reduce the roll-back by pressing the footbrake.
Brake pedal feels different. When adaptive cruise control is operating normally or when the HOLD function is active, the brake pedal may feel different and you may hear hydraulic noises. Pressing the footbrake while the HOLD function is active can cause pulsations in the pedal.
This behavior is normal for the system.
It is not a fault.
Porsche Hill Control (PHC)
Porsche Hill Control is an assistance system that helps the driver when driving slowly downhill at speeds of between approx. 2 mph (3 km/h) and 20 mph (30 km/h), e.g. on steep slopes or on wintry mountain roads, both when driving forward and reversing.
The system limits the speed by braking on all four wheels. ABS remains active to prevent the wheels from locking.
On vehicles with manual transmission, the system adapts the speed in such a way that the engine is not braked at idle speed.
Like all brakes, the braking ability of Porsche Hill Control is impaired on slippery surfaces (e.g. on icy roads or loose surfaces).
Reduced braking ability on a slippery surface.