# SAT electronic audit: how to prepare documentation for vehicle reimbursements

> Guide to responding to SAT electronic reviews via Buzón Tributario with legal deadlines and monthly XML accounting.

**Author:** Rodrigo Vázquez — Mexican Tax Specialist (SAT, CFDI)  
**Published:** 2026-04-28  
**Updated:** 2026-04-28  
**URL:** https://quilometragem.com/blog/sat-electronic-audit-how-to-prepare-documentation-for-vehicle-reimbursements

**TL;DR:** Guide to responding to SAT electronic reviews via Buzón Tributario with legal deadlines and monthly XML accounting.

- The electronic review is a verification power under article 53-B of the Federal Tax Code that lets SAT audit taxpayers entirely through digital channels.
- The Buzón is the official electronic notification system.
- SAT detects inconsistencies through CFDI cross-matching and issues a provisional resolution with a preliminary assessment.
- Fifteen days to rebut the provisional resolution, ten additional days for a second information request and forty days for SAT to issue the final resolution.
- Keep a detailed logbook (origin, destination, date, kilometers, business purpose), fuel CFDI with electronic payment, an internal policy signed by management, transfer receipts to the employee and a reconciliation between the log and the CFDI.

## What is a SAT electronic audit

The electronic review is a verification power under article 53-B of the Federal Tax Code that lets SAT audit taxpayers entirely through digital channels[^cff-53b]. All communication runs through the Buzón Tributario, mandatory for legal entities since 2014[^buzon-sat].

## Buzón Tributario as the single channel

The Buzón is the official electronic notification system. SAT publishes resolutions and notices and the taxpayer must check the inbox at least every three calendar days. A notification is deemed served on the fourth business day after delivery if the document is not opened[^buzon-sat].

## Typical review sequence

SAT detects inconsistencies through CFDI cross-matching and issues a provisional resolution with a preliminary assessment. The taxpayer has fifteen business days to present evidence or accept with a 20% penalty discount[^cff-53b].

## Legal deadlines

Fifteen days to rebut the provisional resolution, ten additional days for a second information request and forty days for SAT to issue the final resolution. All deadlines are business days starting the day after effective notification.

## Minimum documentation for vehicle reimbursements

Keep a detailed logbook (origin, destination, date, kilometers, business purpose), fuel CFDI with electronic payment, an internal policy signed by management, transfer receipts to the employee and a reconciliation between the log and the CFDI[^cfdi-guia].

## Monthly XML electronic accounting

Legal entities file the trial balance and chart of accounts monthly in XML following Annex 24. Reimbursement accounts must use the SAT grouping code and tie to the annual return.

## Response strategy

Validate the notice authenticity on the SAT portal, organize evidence in a PDF signed with the e.firma and upload it to the Buzón with a numbered index.

## Errors that cost deductions

Generic logbooks, fuel CFDI paid in cash above two thousand pesos, outdated policies and accounts outside the chart filed in electronic accounting are the most common findings. Keep all evidence for five years under article 30 of the Federal Tax Code.

## Frequently asked questions

### How many days do I have to respond to a provisional resolution?

Fifteen business days from the day after the effective notification in the Buzón Tributario.

### What happens if I do not open the SAT notice?

It is deemed served on the fourth business day after delivery and deadlines start running automatically.

### How long must I keep the documentation?

Five years from the filing date of the annual return under article 30 of the Federal Tax Code.

## Sources

- [Código Fiscal de la Federación, artículo 53-B (revisiones electrónicas)](https://www.diputados.gob.mx/LeyesBiblio/pdf/CFF.pdf) — Cámara de Diputados (2026-04-28)
- [Buzón Tributario - SAT](https://www.sat.gob.mx/personas/buzon-tributario) — Servicio de Administración Tributaria (2026-04-28)
- [Guía de llenado del CFDI 4.0](https://www.sat.gob.mx/consultas/35025/formato-de-factura-electronica-(anexo-20)) — Servicio de Administración Tributaria (2026-04-28)