| If you are an end user and the copy quality looks normal, I would tell you to ignore it until the next time you need service. The Surface Potential sensor doesn't really do that much and usually if it has a problem, it affects your image quality. Also if it were to be defective, we usually just turn it off as the machine doesn't care much that way.
If you are a tech, I'd say reset the sensor (08-420 to 0), clean it and inspect components around it. If the code returns, disable sensor (08-421 set to 1) and go about your business. | 
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