All You Need To Know About Aftermarket ECUs

"The benefits of Aftermarket ECU's and alternative options."

Some cars cannot be mapped, the ECU's are generally locked and need to be unlocked. Manufacturers don't really want people messing with their code so they fit checksums in the map tables which must be validated to prevent tampering.

When cars are popular and have a demand for engine tuning/remapping then much time and effort can be expended in developing a tune/remap option for them. However for older models and those which are not so popular the only option is to bypass your cars ECU completely.

In some instances, for example, in the case of large power gains, additional forced induction and twin sets of fuel injectors a car is pushed far and beyond.what the stock ECU can handle, so you either compromise your mods and power, or look to get a better performing ECU.

What Is An Aftermarket ECU?

An aftermarket ECU is an electronic control unit that, unlike the ECU installed by your OEM, allows you to get the most out of your vehicle.

Normally, stock ECUs are restricted for a variety of reasons. The automakers have to stick to several international standards and typically select options that, rather than focusing on peak performance, prioritize the life of the various vehicle components.

Aftermarket ECUs for specific vehicle models and purposes are ubiquitous on the market as people around the globe love modifying their cars to increase their output.

The main functions of aftermarket ECUs include increasing the car's performance, assisting in passing emissions tests, and improving fuel efficiency.

Why Is An Aftermarket ECU Better?

The factory-fitted ECUs have been designed to last for a longer period. However, meanwhile, they compromise the car’s performance.

They have a limited number of possibilities and in the case of many Japanese manufacturers, the factory fitted ECUs cannot be remapped.

This is a significant performance barrier, and in such cases, aftermarket ECUs demonstrate their worth by allowing interested individuals to boost the performance of their vehicles to new heights.

How Does An Aftermarket ECU Work?

All ECUs operate on the same basic principle. They take input from various sensors, such as engine load, intake temperature, and RPMs, and then make decisions based on the purpose for which they were installed.

As previously stated, aftermarket ECUs are designed for specific purposes, and as a result, the ECU behaves as programmed.

For example, an aftermarket ECU designed to improve fuel average will take the input and then determine the best setting for optimizing fuel consumption.

Wiring Harnesses

When installing an ECU, it is critical to consider what you intend to do with your wiring harness.

Stock Wiring Harness

If you want to use the factory-installed wiring harness, the Plug n Play ECU options are your best bet.

These ECUs can be connected to the car’s stock wiring harness with the help of an adaptor. It allows one brand of aftermarket ECU to be installed in many different cars.

Aftermarket Wiring Harness

If you want to get extra performance and swap out your car's engine, the Universal ECUs offered by various manufacturers is the way to go.

In this case, you will be required to use a different wiring harness. Two options exist in this scenario which includes:

Universal wiring harness

Engine specific harness is also known as the terminated engine harness.

Setting up an aftermarket ECU requires a little specialist knowledge.

Most can be set to a learning mode, where it will adjust the map and setting on the fly as the engine is running, this is a great way to establish a base line. Indeed most factory ECU's will trim to a small degree to cope with fuel quality and driving conditions that vary, but the aftermarket ECU takes this to new levels.

Cheaper systems are less forgiving, so you really do get what you pay for, and we would recommend a system that allows full data logging, especially if you've done many mods to your car.

Knock Sensor & Its Importance

To understand the significance of a knock sensor, it is essential to know what knocking is and why it must be avoided.

What Is Knocking?

Knocking is the process of premature ignition of the air and fuel mixture which can result in damage to various engine components.

As a result, experts believe that installing a knock sensor is one of the best investments you can make in your vehicle to extend the life of the engine.

How Knocking Affects Your Car?

If the knocking process continues for an extended period, it can harm the pistons, so spending a little extra for a knock sensor saves you a lot of money in the long run.

Not all aftermarket ECU's have a knock sensor facility, which in our opinion is crazy, as tuned cars are more likely to experience problems related to knock as everything is being pushed the limits.

How Does A Knock Sensor Help

Always go for a setup with a knock sensor as it detects noise in the engine and sends a signal to the ECU which then adjusts the spark timing to resolve the issue from happening again.

How To Setup An Aftermarket ECU?

The first step in setting up an aftermarket ECU is to remove the factory-installed one. However, before proceeding, it is critical to disconnect the battery.

The location of the ECU differs depending on the make and model of your vehicle. ECUs, on the other hand, are typically housed in a metallic box with a plastic cover to prevent moisture ingress.

Before removing the existing ECU, the main harness must be removed; after removing the bolts that hold the stock ECU in place, the ECU comes off as a single metallic piece.

After this, all that is left is to install the aftermarket ECU and install the wiring harness. Reconnect the battery and check whether or not the car is working properly.


We've seen a few installations of aftermarket ECU's where the car won't unlock or start, and this is usually traced to the immobilizer in the car or the way the cars security is setup and is not a fault of the aftermarket ECU, but will require an alternative solution.

ECU Brands For Different Car Models

ECUs, like all other vehicle parts, are manufactured by a variety of companies. Haltech, HKS, Bosch Motorsport, Siemens, LINK, DTA Fast, AEM, and MBE are among them.

Let's take a look at a few vehicles from industry leaders and talk about the various ECUs for them.

  • BMW 5 Series 530 3000D
    In the case of a BMW 5 Series (E60) with a 530 3000D engine having M57D30OLTU engine type that has 235 HP.
    The Bosch ECU version for this model is EDC16+ C35
  • Audi A6 3000 V6 TDI
    For an Audi A6 3000 C6 6 TDI having ASB engine type that has 233 HP, the Bosch EDC16CP34 ECU is used. Siemens ECU's tend to be used on cars with DPF filters to meet Euro VI.
  • Mercedes S W221 S420 4000 CDI
    The BOSCH EDC16+ CP31/CP36 ECU is used for a Mercedes Benz S W221 with S420 4000 CDI engine (Type OM629).

The Bosch ECU's are generally favored and have lots of support in the "ECU tuning" world, primarily because they are quite protective of the engine, so if you get it wrong you are not left with a broken engine, just one stuck in limp home mode.

Different ECU's were used primarily to match ever stringent fuel regulations, with fuel injection systems becoming ever more complex and requiring feedback from more sensors around the engine and exhaust. Performance of the ECU is also a factor, the faster it can process the data the more quickly it can respond with adjustments to maximize efficiency.

Alternatives To Aftermarket ECUs

If you want to put your vehicle on steroids quickly, an aftermarket standalone ECU is a great option. However, because of the drawbacks of these devices, some people prefer not to use them.

There are modules that plug in and extend a stock ECU, the Hondata unit is one such example, allowing the addition of a turbo, data logging and mapping capabilities.

In such cases, different options exist that, while not as powerful as a standalone ECU, deliver significantly better results than the stock variants.


Piggyback ECUs, for example, are wired to the stock ECU and thus improve the car's performance.

If you are not a car guy, one simple way to tell if you have a piggyback installed is to check if the stock ECU is still in your car, and if it is controlling any part of the motor, you have an added piggyback ECU.

Chip Tuning

Chip tuning is yet another method for enhancing a vehicle's performance. The programmable ROM (Read Only Memory) chip in your vehicle's ECU will be changed or modified to accomplish this.

This means that simply replacing a chip will significantly improve the performance of your vehicle.



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