Williams were hit with a 60,000 euro fine by the Japanese stewards after Pastor Maldonado lost a wheel during Friday's practice.
The Williams driver was put into a spin at the Spoon Curve in FP1 at which time his rear left wheel was seen rolling loose away from car.
As a loose wheel is a breach of the regulations and regarded as a serious safety issue, the F1 team was handed a fine.
However, the stewards pointed out that it wasn't a mechanical failure but rather human error.
"Examination of the parts concerned revealed that the wheel fastener had not been completely fastened, thus not engaging the first retaining plunger," said a statement from the stewards.
"The secondary retaining plunger failed to keep the wheel in place."
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