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Fault phenomenon: vehicle in idle state of normal power, but when the speed exceeds 20km/h, the steering sinks, and as the speed increases, the steering becomes heavier. When the vehicle stops completely, the steering will return to normal. Inspection and analysis: IDS test, no fault code storage; the road test for the car, all normal; the car to the lift to check the steering wheel state, no interference phenomenon. Detection of front wheel alignment parameters, tilt angle and toe in data are all within normal limits. A careful examination of the chassis of the vehicle failed to detect any signs of collision. It also passed through the main trench, confirming that no accident occurred. 10S is used to reprogram the power steering control unit, but failure after programming continues. No exception is found in data traffic comparison with other vehicles. Considering that the new Carnival vehicle uses an electric power steering system (EPAS), the EPAS is only provided by the power steering motor that is independent from the engine when it is steering, and the motor will stop running when it is not turned, unlike the traditional hydraulic power steering pump, as long as the engine is working all the time. . At the same time, the EPAS control unit receives the speed, speed and other signals supplied from other control units, and controls the current of the power steering motor combined with the torque sensor signal, thus controlling the size of the steering power. It is judged that the EPAS control unit may have intermittent faults resulting in heavy steering. As the EPAS control unit and the steering column are a assembly, it is not dismantable, so a new steering column assembly is replaced, but the post programming failure still exists. Redefine the maintenance idea and carefully analyze the possible problems. Due to the replacement of the steering column assembly, the relevant lines were inspected, so the problems of electrical components and lines could be eliminated. Now, the most likely problem is mechanical parts. The most likely problem is the steering gear. After dismantling the dustproof sleeve of the steering gear, it is found that the steering gear rack and the steering gear shell are not in the center line, thus it is concluded that the steering gear internal deformation leads to the heavy steering. Elimination method: replace the steering gear.