If your vehicle is showing sudden loss of power steering assist while driving, here are the most likely causes and the parts you'll need to fix each one.
The drive belt that spins the power steering pump snapped or slipped off the pulleys, instantly cutting off hydraulic pressure. This is often accompanied by the battery warning light coming on if it also drives the alternator.
A high-pressure hydraulic line ruptured, causing a massive and sudden loss of power steering fluid. You will typically hear a pop and see a large puddle of fluid under the vehicle.
On modern vehicles without hydraulic fluid, the electric steering motor or its control relay can overheat or fail electrically, causing the system to shut down to prevent further damage.
The internal components of the hydraulic power steering pump shattered or the pump shaft sheared off, completely stopping fluid circulation to the steering rack.
Electric power steering requires massive electrical current. If the alternator fails while driving, the vehicle's computer will often disable the EPS system to save remaining battery power for the engine.
If the drive belt or tensioner was recently replaced but not tightened or routed correctly, the belt can easily slip off the pulleys during normal driving, killing the power steering.
The internal seals inside the steering rack blew out completely, bypassing all hydraulic assist. This is rare but causes an immediate heavy steering feel even if the pump is working.