A cold storage warehouse reported that a Hyundai 35D-7E electric forklift made a loud whining noise whenever the steering wheel was turned. After 10 minutes of continuous driving, the "Electric Power Steering (EPS) Overheat" warning light illuminated, and the steering became entirely manual (extremely heavy) until the motor cooled down.
The technician first connected the EPS diagnostic tool. The live data showed the EPS motor drawing 45 Amps continuously while turning, well above the normal 15-20 Amp range. The high current was triggering the thermal protection switch in the EPS controller. To find the source of the mechanical resistance, he lifted the rear of the forklift and disconnected the EPS motor from the steering gear. The motor spun freely and quietly, indicating the problem was in the mechanical steering linkage.
He removed the "Steer Knuckle Thrust Bearing" (the bearing that carries the vertical load of the rear axle on the steering pivot). The bearing had completely failed; the steel balls had shattered, and the bearing races were grinding metal-to-metal. The immense friction required to turn the axle was what overloaded the EPS motor.
Additionally, he found the "Torque Sensor" (a magnetic sensor on the steering input shaft that tells the motor how much assist to provide) had slipped out of alignment. The misaligned sensor was sending a false signal that the operator was constantly turning the wheel hard, commanding the motor to draw maximum current even when driving straight, which generated the whining noise and excessive heat.
The repair involved replacing the steer knuckle thrust bearing and races. The steering kingpins were lubricated with low-temperature synthetic grease. The torque sensor was re-calibrated using the diagnostic tool and locked into the correct position with thread-locking adhesive. After reassembly, the EPS motor current dropped to 12 Amps during turns, the whine disappeared, and the overheat trips ceased entirely.
