ok guys, got (3) codes from my monthly scanner check. I currently have NO CEL on.

335 = EGR sensor circuit voltage higher or lower then expected during self-test.

336 = EGR sensor circuit voltage higher then expected.

543 = Fuel pump secondary circuit fault.

now i know the first 2 are related.

any advice on finding the problems of these codes?

1994 3.0 supercab xl 4x4 5-speed with 168,000 miles.