Calling the Engine Control Unit “The Vehicle’s Brain” would be the most accurate definition of it.

Just like a human body can’t function without the brain, the similar way, a vehicle can’t run without the Engine Control Unit.

This part of the vehicle regulates most of the functions related to the engine from determining the amount of fuel injected into the cylinders to the working of the ABS brake system.

If anything goes wrong with the Engine Control Unit, the whole performance of the vehicle gets affected. In some scenarios, it’s possible you would not be able to operate your vehicle at all. But fortunately, there is a range of signs and symptoms of a bad engine control units that can indicate you of trouble before the condition of the unit gets worse.

Here are the symptoms failing ECU that you should not overlook. And if you notice any of these systems you should take your vehicle to the nearest mechanic immediately.

Signs and Symptoms of Bad Engine Control Unit (ECU)

#1 – Check Engine Light

The most common sign of a bad Engine Control Unit is the illuminated check engine light that does not go off. Generally, the check engine light goes off when the issue is resolved. But if ECU is defective, the check engine light may remain illuminated. This indicates there is some issue with the Engine Control Unit itself that needs to be inspected by a professional.

Also, Read: How to Reset Check Engine Light

#2 – Engine Stalling

Another sign of a faulty Engine Control Unit is the engine stalling. However, there are many other reasons also that can cause engine stalling but if you notice an indefinite pattern of engine stalling, this could be due to a bad Engine Control Unit. In other words, if the engine stalls very often but without any consistency, there is a high possibility of a faulty ECU in your vehicle.

As you know ECU manages the functions of the engine through the data it receives through its various sensors. If it becomes faulty, the whole performance of the vehicle gets affected. Therefore, you should approach an expert mechanic at the first stalling you experience with the vehicle.

#3 – Engine Not Starting Up

A vehicle needs some data to function efficiently and this data it receives from the ECU. If this unit has any fault, it may stop sending the data to the engine and due to that, the engine may stop functioning.

However, there are many other reasons for the ignition problem so it’s possible you would not take it much seriously. But if you face the ignition problem constantly, ECU may be the main culprit.

#4 – Poor Fuel Economy

When your vehicle has a faulty ECU, the fuel consumption is severely affected. This happens because the ECU doesn’t send any information about the quantity of fuel the engine needs for the internal combustion process. The fuel injectors may inject more fuel than normal to keep the engine running. This will result in paying more money on fuel.

Therefore, if you notice, your vehicle is consuming more fuel than normal, you must get inspected the ECU of your vehicle.

How Much Does an Engine Control Unit Replacement Cost

Once you have diagnosed and found trouble with the Engine Control Unit, the next important step is to determine whether you need replacement or repair. If there is a minor fault with any of the sensors, then go for repair only. But if the Engine Control Unit has damaged or has some bigger fault, then replacement is the only choice.

As you know, ECU is the most sophisticated part of the vehicle and installation is also not straight-forward. Therefore, the replacement cost of the ECU can be very high, depends on various factors including the rarity of parts, difficulty of the vehicle, and the location.

It can cost you between $800 and $1000 for parts. And labor cost is estimated between $80 and $150. Thus, the total cost can come around $950 to $1150.

If you have a top model car, the replacement cost can be higher than this average cost. It can cost you several thousand dollars. The reason for its high replacement cost is mainly its sophisticated construction that includes a number of sensors, components, and intricate wiring and testing post-installation is also time-consuming.

You can make a huge saving on the replacement of ECU if you consider used or refurbished ECUs. This can be an excellent option for those who are short on budget but want their vehicle to run perfectly.


Since ECU is a quite sensitive and expensive part of the vehicle, you should not try to repair it on your own until you have enough knowledge else it can cause you more trouble. Here, the most important task for you is to pay close attention to the symptoms, and if you suspect the failing of ECU, get your vehicle diagnosed by an expert mechanic who can perform a thorough diagnostic scan of the unit and do the needful.