# For used-car dealers

> For used-car dealers: pre-purchase diagnostics, back to stock software, missing keys and electronic faults that hold up a sale.

- URL: https://www.reprogramacionesmbv.com/en/trade/car-dealers/
- Index for AI (llms.txt): https://www.reprogramacionesmbv.com/en/llms.txt
- Versión en español: https://www.reprogramacionesmbv.com/profesionales/compraventas/
- Reviewed: 2026-10-15

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Some cars arrive on the forecourt and never leave. It is hardly ever the bodywork: it is a single key, a warning light the buyer sees on the test drive or software a previous owner tampered with. This is about spotting it before you buy and fixing it before you sell.

**In short:** Reprogramaciones MBV helps used-car dealers in the Community of Madrid with the electronic problems that hold up the sale of a stock car: making a key when only one or none is left, diagnosing warning lights, restoring the original software on a car a previous owner remapped or had a delete done on, and checking a car's electronics before you buy it. We come to your showroom or vehicle compound, or you bring the cars to the workshop in Alcalá de Henares. We do not tamper with mileage or hide faults: we put the car right or tell you what is wrong with it. Price on request per car and job.

## Why a stock car does not sell

A buyer will forgive a scratch, but not a warning light on the test drive or being told there is only one key. And what brings them back angry a month later is a car that fails its ITV (Spain's compulsory periodic vehicle inspection, similar to the UK MOT) because someone before you tampered with the software. These are the electronic problems that keep a car sitting on the forecourt the longest:

| Problem | Why it holds up the sale | What we do |
|---|---|---|
| Only one key, or none | The buyer notices when signing and asks for a discount, or walks away | Program a new key into the immobiliser. See [keys](https://www.reprogramacionesmbv.com/en/car-keys/) |
| Engine or airbag warning light on | It shows on the test drive and creates distrust | Find the cause and quote for the repair. See [diagnostics](https://www.reprogramacionesmbv.com/en/vehicle-diagnostics/) |
| Software remapped by the previous owner | Risk of faults, of rejection by a main dealer and of a complaint | Return to factory software. See [original software](https://www.reprogramacionesmbv.com/en/back-to-stock-software/) |
| Particulate filter, EGR or AdBlue deleted | The car fails the ITV and cannot be sold properly | Restore the original software and, if the part is missing, refit it |
| Instrument display faults | It looks like a neglected car even when it is not | [Instrument cluster repair](https://www.reprogramacionesmbv.com/en/instrument-cluster-repair/) |
| Jerky automatic gearbox | The buyer notices in the first few metres | Check adaptations and software. See [automatic gearboxes](https://www.reprogramacionesmbv.com/en/automatic-gearbox-tuning/) |

## Before buying: the electronic check

The best time to find these problems is before you pay for the car, not afterwards. If you are going to take a vehicle into stock and you have access to it, we can check it:

1. **Reading every control unit**: not just the engine one. Comfort, airbag or gearbox faults cost money too.
2. **Code history**: a recently cleared code leaves clues. If someone wiped the memory before selling you the car, that is something you want to know.
3. **Engine software**: we compare it with the factory software for that engine and look for signs of a remap or a delete.
4. **Physical check**: whether the particulate filter, the catalytic converter and the EGR are still fitted and working.
5. **Keys**: how many there are and whether they are all programmed.
6. **Written report**: we give you the diagnostic result in writing, with what we have found and what it would cost to fix, so you can take it into account when negotiating the purchase price.

## Getting the car ready for sale and for the ITV

If the car is already in your stock with modified software, the advisable thing is to return it to stock before selling it. Under Real Decreto 920/2017 (Spain's vehicle inspection regulation), a car with an emissions control system that is missing, modified or not working has a **major defect** at the ITV, and the inspection is a fail.

How it goes back to stock depends on what we find:

- **If the component is still fitted**, writing factory software back to the ECU is normally enough.
- **If the part was removed or emptied** (a particulate filter, a catalytic converter), a new one has to be fitted before the system can work again.
- **If nobody saved the original**, we look for the factory software that matches that ECU. We explain it under [back to stock software](https://www.reprogramacionesmbv.com/en/back-to-stock-software/).

What we do not do is "legalise" a car or promise it will pass an inspection: we leave the system as the manufacturer designed it, and the ITV result depends on the condition of the whole vehicle.

## What we do not do, even if it would help a sale

- **Touch the mileage.** It deceives the buyer and we do not do it under any circumstances.
- **Hide a fault** by clearing codes or disabling the warning light.
- **Delete emissions control systems** on cars that will be driven on the road, however expensive the fault. The reasons are under [deletes](https://www.reprogramacionesmbv.com/en/deletes/).

## Several cars, one visit

Used-car dealers rarely have just one car waiting. Send us the list with the make, model, year and problem of each one and we will arrange a visit to your showroom or compound to do them together. If any of them needs units removed, we will tell you which one is best brought to the workshop in Alcalá. How our mobile service works is explained under [mobile service](https://www.reprogramacionesmbv.com/en/trade/mobile-service/).

## Price

Each car and each job is **price on request**, quoted before we start. If you are going to bring us several cars, terms and volume pricing are agreed case by case. You can pay in cash, by Bizum (Spanish instant bank payment), by card or by bank transfer.

Send us the car or the list of cars and what is wrong with them. We will tell you what can be done, where and the price per car.

## Frequently asked questions

### Can you clear the fault codes so the car looks clean on the test drive?

We do not clear codes without fixing the cause: the warning light comes back within a few kilometres, usually once the car has been sold. What we do is find out what is causing them and give you a price to fix it, so you can decide whether it is worth it.

### How do I know whether a car I am about to buy has been remapped?

You cannot tell by looking. Reading the engine ECU lets us compare the software it has with the factory software for that engine and see whether there are signs of modification. Checking that the particulate filter and the catalytic converter are still fitted is another check worth doing at the same time.

### I have several cars of the same make with only one key each. Can it all be done on the same day?

If they are in the same place and the systems allow it, we arrange a single visit. Send us the list with the model, year and chassis number of each one and we will tell you what can be done and the price per car.

### Do you give me anything in writing about the car's electronic condition?

We tell you what we have read and what we have found on each car. If you need that result in a specific format for your sales process, let us know when you book the job.

## Sources

- [Royal Decree 920/2017 regulating vehicle inspection (ITV), Annex I, sections 8.2.1.1 and 8.2.2.1 (BOE, Spain's official gazette)](https://www.boe.es/buscar/act.php?id=BOE-A-2017-12841)