Your Complete Guide to Buying ECUs/Computers for Cars

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Your Complete Guide to Buying ECUs/Computers for Cars

Most modern cars come with engine control units, or ECUs, which are nothing but computers that control a series of functions to ensure that cars perform at optimum levels. Also referred to as powertrain control modules, or PCMs, these computers are hardwired into various parts of a car, monitoring and managing aspects like fuel economy, emissions, and a range of other functions. ECUs gather data from sensors located at various parts, analyse it, and take suitable action in accordance.

If you are looking at buying an ECU/computer for your car, you have the option to visit spare part dealers to look for new ones, and you can also approach local car repair shops to see if you can find a compatible, used ECU. Alternatively, you also have the option to look online through websites like eBay, which can be particularly useful, given the number of alternatives you can come by in a single place. Before investing in an ECU, though, it is best that you know how they work, whether you need one in the first place, what you need, and if you can do with ECU remapping instead.

How ECUs/Computers Work

ECUs/computers found in most modern cars rely on microprocessors that work in the real-time processing of data inputs from sensors located within the engine, and they are comprised of hardware as well as software. The hardware comprises of a printed circuit board that is home to a variety of electronic components apart from the CPU, and the software can be found stored within the CPU, flash memory, or EPROMs. An ECU, for example, can sense that the engine requires increased flow of fuel in particular instances, and can accordingly command the injectors to inject more fuel.

Programmable ECUs

A number of ECUs found on the market can be reprogrammed, that is, the way they behave can be changed. Take into account that factory-fitted ECUs tend to come with fixed tuning and calibration parameters, and adjusting these, in a number of instances, is near impossible. As a result, if you have made considerable modifications to your car's engine, you may well require a programmable ECU. On the other hand, if the factory-fitted ECU is reprogrammable, making adjustments should be easy.

Changing the settings of a programmable ECU is quite simple, and all that is required is connecting the ECU to a computer through a USB or serial cable, and making the required changes through relevant software.

Aftermarket ECUs

Even in cars that come with programmable ECUs, it has been noticed that they tend to have limitations in comparison to what is offered by various aftermarket ECUs. Good aftermarket ECUs do way more than control ignition timing and fuel injection, they are also capable of controlling functions like speed and traction control, boost control, intercooler spraying, as well as devices like servo motors, fans, and pumps.

Do You Need a New ECU?

Most modern cars, as mentioned, come with inbuilt ECUs, which are designed to cater to driving conditions as foreseen by manufacturers, which, in a majority of cases, is everyday driving by typical drivers. Modifications made to a car can send the manufacturer-supplied ECU in a tizzy, causing it to malfunction or not function at all, and if it cannot be reprogrammed, you need a new ECU. On the other hand, if you have made no modifications but your car's existing ECU does not seem to be working as it should, you, too, may need a new ECU.

Signs That Can Indicate a Faulty ECU

If your car refuses to start and you cannot quite figure out why even after checking its starter, battery, and fuses, it may point to a faulty ECU. If the engine light does not go off, it may have something to do with a faulty ECU. Cars that come with automatic transmission can face gear-shifting problems coupled with jerking, owing to faulty ECUs. In addition, unexplained drops in power or fuel economy could also be attributed to a faulty ECU. Checking if the fault can be fixed before you look for a new ECU is definitely suggested, although you should make sure you choose a centre that carries suitable diagnostic equipment.

What Should You Look For?

Buyers should take into account that they have the option to choose between ECUs that offer dedicated control to suit certain functionalities, and ECUs that offer greater versatility. Moreover, buyers also have the option to look for dedicated models that are designed for specific engine types, which can prove to be more cost effective in comparison to models that offer maximum versatility. The number of input and output points with which an ECU comes should be taken into account. While an ECU would require inputs to determine air and engine temperatures, throttle and crank positions, speed, gear position, oil and pressure, and so on, its output points control injection drivers, ignition coils, lights, pumps, air conditioning, and more. Buying an ECU with spare input and output points is a good idea, as this can make way for modifications that are made in the future.

Is ECU Remapping an Option?

If the modifications made to a car are not extensive, and if the car comes with a programmable ECU, looking for a new ECU may not be necessary, and ECU remapping is an option. When remapping is possible, it is not very difficult to accomplish, although it does need access to the right software and associated knowhow. ECU remapping, with the use of onboard diagnostics, wherein a computer is connected to the ECU, accesses the data stored in the ECU's brain, and makes changes to existing maps, as per user requirements. ECU mapping can help increase power, mileage, and life of the engine's components, and it can also help with aspects like timing, maintaining optimum pressure, regulating flow of fuel, and more.

ECU remapping is reversible, it does not require installing new devices, it can be done quite quickly, and it is not very easy to detect. However, remapping ECUs of all cars is not possible, and while some models simply cannot be reprogrammed, some others come with manufacturer-installed locks. In such instances, looking for a new ECU is the way to go.

Other Options

The performance of your car's ECU can be enhanced in two other ways, which include installing ECU chips or piggyback ECUs. However, both types have their advantages and disadvantages.

ECU Chips

Although the use of ECU chips can sound appealing, given that simply adding a new chip to your ECU is supposed to help, know that this is not really the case. ECU chips rarely manage to have the desired effect, and they can hamper a car's drivability, while also posing a threat to its existing ECU.

Piggyback ECUs

Piggyback ECUs are connected in between a car's existing ECU and its sensors. While some work by adjusting sensor readings before they are transmitted to the ECU, some work in modifying output signals, and some others manage to carry out calculations and take control of aspects, like ignition timing and turbo waste control. If you have the required expertise to work with piggyback ECUs, they can offer great flexibility.

Buying ECUs/Computers for Cars on eBay

A definite advantage of shopping for ECUs on eBay is that you can look for an ECU for just about any make of car, with names like Volkswagen, BMW, Renault, Ford, Audi, Vauxhall, Peugeot, Mercedes-Benz, and Alfa Romeo in the list. A similar range is on offer when it comes to ECU manufacturers, and some of the brands you can choose from include: Bosch, Siemens, Denso, Lucas, Magneti Marelli, and Delphi. The choice also extends to the types of ECUs on offer, and while you have the option to look for standard stock model ECUs, you can expect to find highly-versatile, top-of-the-line variants as well.

Another advantage of shopping on eBay is the ability to look for used ECUs. Since a number of car owners tend to replace their existing ECUs in order to upgrade, their used ECUs end up on sites like eBay, which gives buyers like you the ability to save some money. However, if you narrow in on a used ECU, ensuring that it works as it should becomes important.


What a modern day car can do, in addition to its engine's capabilities, also depends on its ECU to a large extent, and it is the ECU that tells the car's engine what it can and cannot do. Buyers should take into account that there are various alternatives when it comes to looking for ECUs, which is why you should establish just why you need a new ECU and what you expect out of it. For example, if you are looking at bettering your car's fuel consumption, you need to look for an ECU in accordance. Investing in a programmable ECU can be a good idea, if you intend to make changes to your car from time to time.

If your car comes with a programmable ECU, and has not been through extensive modifications, ECU remapping may suffice, especially if you are not looking for too much. If the car's existing ECU cannot be reprogrammed, you also have the option to look at piggyback ECUs, although they do not offer as much functionality and versatility as programmable ECUs. For optimum performance, opting for an aftermarket ECU is the way to go.

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