When we take the car to the garage to find out what is wrong with it, certain faults can hit us hard in the pocket. One of them is being told that the car's ECU is faulty and needs to be replaced.
And you may not know it, but the cost of this fault can be quite high. Now, is it possible to install a second-hand ECU from a salvage yard and continue driving the car? It is undoubtedly an option you should consider since it will represent significant savings for you, but can you?
What's more, do you have a clear idea of what an ECU is and why you shouldn't wait to repair it if it starts to fail? Let us reveal everything about this component of your car!
What is a car's ECU?
This vehicle component is technically known as the Engine Control Unit (ECU), being the computer that controls everything in your car.
As you will know, the engine is considered the heart of the car, as it is responsible for managing everything related to fuel. Well, the ECU would be the brain, being in charge of making certain critical decisions based on the information it receives from the sensors, such as:
- Calculating the amount of fuel each cylinder needs.
- The moment at which the spark must fire to start the car.
- Managing exhaust emissions to comply with environmental regulations.
- Monitoring turbo pressure and the cooling system.
And these are just some of the functions this part performs. If it develops a fault, the car becomes immobilised, as it enters what is known as "protection mode", which reduces its power.
What are the main faults of an ECU?
You must be clear that the ECU does not break down "for no reason" — it usually fails due to external factors, such as:
Water leaks
The ECU is not located in a fixed place, as depending on the manufacturer it can be found in one area or another of the bonnet.
Now, a fairly common location is under the windscreen cowl. When the drains are blocked by dirt or leaves, water accumulates and seeps into the ECU, causing corrosion of the connector pins or short-circuiting the internal circuits.
Electrical faults
Car electronics are very sensitive to sudden voltage changes. If the alternator does not regulate the charge properly, or if jump leads are used to start the car incorrectly (reversing the polarity or with high voltage spikes), it can literally "burn" the internal transistors of the ECU.
Vibrations and extreme heat
As we have mentioned, the ECU is not always found in the same place. Sometimes it is located in areas with an intense heat source, such as near the battery.
In addition, there are also the constant vibrations and the continuous temperature changes, which can gradually cause the solder joints on the circuits to crack, leading to faults. These are the most difficult to diagnose.
Sensor failure
The ECU can function because there are various sensors spread throughout the car that send it information.
When these sensors short-circuit, or a cable has worn through and is rubbing against the chassis, an excess of current is produced that feeds back into the ECU. Since it is a part not designed to receive that energy return, the components suffer a short circuit.
Software misuse
From time to time the ECU needs to be reprogrammed, or components are used to do a "workaround" such as the use of low-power chips or interrupted software updates.
When this happens, the ECU becomes locked, preventing the car from starting.
Wear of internal components
Like any computer, capacitors and other electronic components have a limited lifespan. In cars with many years or very high mileage, it is natural for the ECU's circuit board to start failing through sheer exhaustion of its materials.
How much does it cost to replace a car's ECU?
Here we get a little into the topic that interests you most: how much can the ECU replacement cost?
By now it should be clear to you that this is a very important part of the vehicle, and that if it fails, the car will sooner or later not start — right? Well, when you find yourself in this situation you could be facing a mechanical repair job whose price ranges between 1,300 and 3,000 euros, depending on the car model and, of course, what the garage charges for labour.
Can you fit a salvage yard ECU?
We understand that what we've said above may have worried you a little, since it is a very important repair that you will have to carry out no matter what.
Now, is it possible to fit an ECU bought from a salvage yard? You're in for a pleasant surprise: yes, you can buy a second-hand ECU from a salvage yard to repair your vehicle.
In fact, it is the smartest decision, as it will represent enormous savings for your pocket — the part will cost you 80% less than if you bought it new, and the rest will only be what the garage charges you for the repair.
Before you go, let us answer some common questions about buying a second-hand ECU for your car:
Is it necessary to report the replacement?
Not at all — unlike other replacements, such as changing the car's wheels, there is no need to inform the MOT station that you have changed the ECU. As long as it has the same reference number as the original and performs the same function, it will be considered a maintenance repair.
Will any ECU do?
No, and you need to pay very close attention to this if you are going to buy an ECU from a salvage yard.
The one you acquire must have the same reference number (written on the sticker on the part), and be from the same car and model in order to work.
Does the diagnostic test detect the replacement?
During the MOT, a machine is used that connects to the car's OBD port, which is used to check for engine faults and emissions.
When the replacement ECU is fitted, it must have been properly cloned so that the MOT machine can read the car's chassis number and not detect any anomaly.
What to do if the ECU has been reprogrammed?
Another thing you need to check carefully before making your purchase is that the ECU has not been reprogrammed — something common when you want to get more power out of the car. Because if it has, you will have problems during the emissions tests.
In addition to cloning your old ECU, it will be necessary to reprogram it according to the standard software of your model, to ensure that the CO2 values and capacity are within the legal limits.
Is it a part you can replace yourself?
The answer is a "yes and no".
That is, if you are a person with extensive knowledge of mechanics, then you will certainly be able to locate and extract the part easily.
To begin with, extracting the ECU simply requires basic tools such as socket wrenches or Torx keys to release the brackets and disconnect the wire connectors. However, the connections are delicate, so it must be done with great care.
However, the first thing to do is to clone the software from your old ECU, because if you simply swap your old ECU for the one you bought at the salvage yard without cloning it first, it will not work. If you still want to do the swap yourself and save the cost of a mechanic, what you need to do is go to a car electronics laboratory to have the ECU cloned, and then you can fit it without any worries.