# No-start solutions

> Car won't start due to the immobiliser, key, ECU or a module: how to read the symptom, what to check yourself and how we fix it wherever the car is in Madrid.

- URL: https://www.reprogramacionesmbv.com/en/no-start-solutions/
- Index for AI (llms.txt): https://www.reprogramacionesmbv.com/en/llms.txt
- Versión en español: https://www.reprogramacionesmbv.com/soluciones-de-arranque/
- Reviewed: 2026-10-15

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When your car won't start, you don't have time to read much. So let's get to the point: what the car is telling you from what it does, what you can check yourself in five minutes and what we need to come out to wherever it is.

**In short:** When a car won't start because of an electronic fault, the cause is usually the immobiliser (the key isn't recognised), the engine ECU (engine control unit), the comfort module that manages starting (BSI or BCM, body control module) or an essential sensor such as the crankshaft position sensor. What the car does when you try to start it points the diagnosis: it doesn't crank, it cranks but won't start, or it starts and cuts out after a few seconds. We come to wherever the vehicle is in the Community of Madrid (the Madrid region), diagnose it there and, if an ECU has to be replaced, cloning starts from from €100 + VAT (€121 including VAT). Before calling us, check the battery.

## Before you call us: five minutes that could save you the visit

- **Battery**: if the starter motor turns slowly when you turn the key, clicks or the instrument cluster flickers, it's most likely the battery. Try jump leads or a jump starter.
- **Spare key**: if the car starts with the other key, the problem is the key you're using (fob battery, damaged transponder), not the car.
- **Fob battery** on keyless cars: many have a spot on the steering column or centre console where you can rest the key so it's read even if the battery is flat. It's in the handbook.
- **Pedal and lever**: on manuals, clutch fully down; on automatics, lever in P and foot on the brake. A faulty pedal switch prevents starting.
- **Fuel**: it sounds obvious, but a fuel gauge that reads wrong can fool anyone.

If it still won't start after that, note exactly what it does and read on.

## What the car is telling you

| What happens | What it usually means | What we look at first |
|---|---|---|
| **Nothing happens**: the engine doesn't crank and you can't hear the starter | Battery, starter motor, or a module that isn't giving the start command | Voltage, starter motor supply, communication with the BSI or BCM |
| **It cranks but won't start**, with no particular warning light | Lack of fuel, spark or the signal from an essential sensor | Fuel pressure, crankshaft or camshaft sensor, faults stored in the ECU |
| **It cranks but won't start with the key or padlock light** on or flashing | The immobiliser isn't recognising the key | Transponder, reader antenna, pairing between key, immobiliser and ECU |
| **It starts and cuts out** after one or two seconds | Typical of the immobiliser: it lets the engine start and cuts injection when it can't validate the key | Communication between the immobiliser and the engine ECU |
| **The instrument cluster is dead** or there's no communication through the diagnostic socket | A fault in the power supply or the car's communication network, or a control unit that isn't responding | Fuses, earths, CAN network, condition of the ECU |
| **It starts after replacing a control unit… or it doesn't** | Part not paired with the car | Coding and immobiliser data |

This table is a guide; diagnostics confirm it. With diagnostic equipment we can see which control unit isn't responding or what each one has stored, and that avoids changing parts blindly. We explain it on [electronic diagnostics](https://www.reprogramacionesmbv.com/en/vehicle-diagnostics/).

## Immobiliser and keys

The immobiliser is an anti-theft system: the key has a chip (transponder) that the car reads when you try to start it. If the response isn't the expected one, the engine ECU won't allow injection. It fails because of:

- **The key**: a transponder damaged by a knock or water, or a new key that wasn't programmed properly.
- **The reading**: the antenna around the ignition barrel or the reader on keyless cars.
- **The pairing**: after replacing an ECU, the instrument cluster or the immobiliser module, the parts don't recognise each other.

If the problem is the key, or you need a new one, it's all on [keys](https://www.reprogramacionesmbv.com/en/car-keys/). If it's parts that don't recognise each other, the solution is usually cloning.

## Faulty engine ECU or module

An ECU can stop working because of damp, a voltage spike when jump-starting or an internal component failing. When it has to be replaced, a new or second-hand unit doesn't know your car. The most direct solution is **cloning**: copying the data from the faulty unit (including the immobiliser data) onto the replacement, so the car recognises it as its own.

- Engine ECU: [ECU cloning](https://www.reprogramacionesmbv.com/en/ecu-cloning/), from from €100 + VAT (€121 including VAT).
- Comfort module (BSI or BCM), which on many cars manages starting, lights and locks: [BSI cloning](https://www.reprogramacionesmbv.com/en/bsi-cloning/), from from €100 + VAT (€121 including VAT).

If the ECU is so badly damaged it can't be read, we'll tell you and look for another way out.

## We come to where the car is

A car that won't start can't be taken to the workshop without a tow truck, so usually we come to you: to your home, your garage, your company car park or your workshop, anywhere in the Community of Madrid. So we bring what's needed, send us:

**What we need to know**

- Vehicle: Make, model, engine and year
- Where it is: Address and whether it's in the street, in a garage or at a workshop
- What it does: What you saw in the table above (doesn't crank, cranks but won't start, starts and cuts out)
- Warning lights: Whether the key light, the padlock or another warning comes on
- History: Whether anything was changed recently (battery, ECU, key) or whether it got wet
- Keys: How many you have and whether it starts with any of them

With that, we'll tell you what it might be and whether it can be fixed on the spot. If an ECU has to be removed and opened and the location doesn't allow it, we'll suggest bringing the car to the workshop in Alcalá de Henares (Ronda de la Pescadería, 24, bajo, 28801 Alcalá de Henares (Madrid)). Appointments are booked 48 hours in advance, but a car that won't start is usually urgent: we deal with emergencies the same day for an extra charge, which isn't fixed and which we'll tell you when you ask. We come out Monday to Friday, 8:00–14:00 and 16:00–19:30 (closed on Saturday and Sunday), and the call-out is quoted individually. More detail on [mobile service](https://www.reprogramacionesmbv.com/en/trade/mobile-service/).

## Price

No-start diagnostics are **price on request**, depending on the vehicle and the call-out. If the solution involves cloning a control unit, engine ECU cloning starts from from €100 + VAT (€121 including VAT) and BSI cloning from from €100 + VAT (€121 including VAT). We give you the price before doing any work.

Send us the vehicle, where it is and what it does when you try to start it. We'll tell you what it might be and how we'll fix it.

## Frequently asked questions

### Can it be just the battery even if the lights come on?

Yes. The instrument cluster lights use very little power and can come on with a battery that no longer has the strength to turn the starter motor. On top of that, at low voltage some control units don't communicate properly and the car shows warnings that look like something else. It's the first thing we check.

### What if I've lost all my keys?

Then the problem isn't a no-start but a key issue: new keys have to be programmed into the car's immobiliser. We explain it on [keys](https://www.reprogramacionesmbv.com/en/car-keys/).

### Can you remove the immobiliser to get me out of trouble?

On a road car, that's not the solution: the immobiliser is an anti-theft protection and your insurer may require it. What we do is find out why it isn't recognising the key and fix that, or clone the ECU if that's what has failed.

### I bought a second-hand ECU and the car won't start. Why?

Because that ECU is paired with another car's immobiliser and keys. It has to be adapted to yours or, better still, have your original ECU's data cloned onto it. We explain it on [ECU cloning](https://www.reprogramacionesmbv.com/en/ecu-cloning/).

### Do I need to have the car towed to the workshop?

Not necessarily: we come to wherever it is, within the Community of Madrid, as long as there's a mains socket nearby. Only if an ECU has to be removed and opened somewhere it can't be done safely will we suggest bringing it to the workshop in Alcalá de Henares.