Original w2 did not reflect employer HSA contributions Box 12a. Received an w2-C from my employer with the correct information in box 12a. Do i need to file an amendment?

The correction to the W-2 could change a little or a lot on your return, and you won't know which until you go through the amendment process in TurboTax. The change could create or eliminate an excess contribution in TurboTax.

Also, the employer should have removed the box 12 code W amount from your Wages in boxes 1, 3, and 5 on your original W-2. Did they remove the correct amount the first time? Did they change Wages on the corrected W-2? If yes to changing Wages, you definitely need to file an amended federal and state return. You must ask your employer if they have taken the correct amount out of Wages, in case they made two mistakes instead of one.

The code W amount appears on your 8889, but might not have any effect on the rest of the return. In this case, if you choose not to amend because your AGI and tax due don't change, you need to keep good records, in case the IRS notices some discrepancies and writes you a letter for an explanation.

If, however, your state return is from one of three states (California, Alabama, and New Jersey), then you must file an amended state return (which will require you to amend the federal anyway), because HSA contributions are not deductible in these states, and the amount of the contributions (i.e., the code W amount) is added back to state income.

My original W-2 had 12a as "C $65.01". The W2-C has corrected 12a to "W $545.87". There is no change to wages reported on my corrected W-2. The corrected W2 only has correction for the 12a box.

So you confirmed that the $545.87 was removed from Wages the first time around? That would be good.

As for the code C, do you still have a taxable cost of group-term life insurance coverage over $50,000? If you have group life insurance from your employer for more than $50,000, you have to pay the tax on the premium for the amount over $50,000, so the code C amount should be added to Wages.

When they removed the C, did they remove the amount of taxable premium from Wages? Or was it never there in the first place?