Default tax code missing when creating a purchase order

[SAPSupport]

I have maintained the tax indicators, set up the "Maintain Default Values for Tax Codes " configuration in CBC, and still the system determines the "V1" tax code in purchase order.

We would like to have the "V3" tax code as a default tax code.

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[SAPSupport · Accepted solution]

The tax code determination logic in the Purchase Order is explained in the note 501054 FAQ: Taxes in purchasing
(See Question 1 the logic of which still applies in cloud)

1. Question:
How is the tax code determined in purchase orders?

Answer:
In the standard system, the system considers the following sources for the tax code(in this sequence): Reference item, contract, request for quotation, info record. It can also be entered manually.
Furthermore, the tax code can be automatically determined via the condition technique. This then has priority.
For the determination of the tax code via the condition technique, condition type NAVS with assigned access sequence 003 is available in the standard system. With Transactions MEK1/MEK2, depending on tax indicators (material, plant, account assignment, origin) you can define different tax codes in the condition tables.
In principle, you can assign this access sequence also to other condition types. The tax code is only transferred to the purchase order if class 'D' (taxes) is the condition type. If there are several condition types of this class in the condition schema, then the first condition schema which contains a tax code has priority.

In the cloud if you wanted to change your tax code in the condition record it can be done via APP Set Tax Rates - Purchasing (MEK2) 
https://fioriappslibrary.hana.ondemand.com/sap/fix/externalViewer/#/detail/Apps('MEK2')/S15

To clarify the standard system behaviour.
When you create a PO the system will try to pick up a default tax code:
1) From any reference purchasing document or purchasing requisition.
2) If there is no reference document the tax code will be taken from the purchasing info record
3) If there is no purchasing info record the field will remain blank.
4) If you have a condition record maintained in 'Set Tax Rates - Purchasing' (MEK2) then the system
will overwrite anything that was found previously with the tax code from the TTX1 condition.