ECU Repair

Engine Control Units are one of the core workings in any modern vehicle, failure of this device will often result in the vehicle refusing to function properly or at all. Although ECUs are sealed with a water tight adhesive, water damage is still the most common problem faced when dealing with faulty or damaged ECUs. Moisture is still able to leak into the control unit by bypassing the water tight seal and seeping through the loom. Other common ECU faults are listed below:

  • Short circuiting
  • Broken pins
  • Broken tracks on the PCB
  • Cold solder joints
  • Corrosion

There are many reasons why your ECU could be faulty. We can save you both time and money by determining the problem and fixing it for a fraction of the price of an ECU replacement. The list below is symptoms of a failing control unit:

  • Check engine light persists after resetting
  • Car was jump started on reverse polarity
  • Engine turning off randomly
  • Loss of injection pulse or fuel pump
  • Intermittent starting problems
  • Loss of communication between the ECU and the scanner
  • Control module memory checksum error

What is an ECU?

The use of the term ECU may be used to refer to an Engine Control Unit, however ECU also refers to an Electronic Control Unit, which is a component of any automotive mechatronic system, not just for the control of an engine.

What does an ECU do?

Fundamentally, the engine ECU controls the injection of the fuel and, in petrol engines, the timing of the spark to ignite it. It determines the position of the engine’s internals using a Crankshaft Position Sensor so that the injectors and ignition system are activated at precisely the correct time.  While this sounds like something that can be done mechanically (and was in the past), there’s now a bit more to it than that.

An internal combustion engine is essentially a big air pump that powers itself using fuel. As the air is sucked in, enough fuel has to be provided to create power to sustain the engine’s operation while having a useful amount left over to propel the car when required.

This combination of air and fuel is called a ‘mixture’. Too much mixture and the engine will be full throttle, too little and the engine will not be able to power itself or the car.

Not only is the amount of mixture important, but the ratio of that mixture has to be correct. Too much fuel – too little oxygen, and the combustion is dirty and wasteful. Too little fuel – too much oxygen makes the combustion slow and weak.

Basic ECU function

The first stage of ECU operation is in fact power management. This is where various voltages are regulated and the power-up of the ECU is handled. Most ECUs have sophisticated power management due to the variety of components inside, accurately regulating 1.8V, 2.6V, 3.3V, 5V, 30V and upto 250V all from the car’s 10-15V supply. The power management system also allows the ECU to have full control over when it powers itself down – i.e. not necessarily when you turn off the ignition switch.

Once the correct voltages are supplied, the microprocessors can begin to boot up. Here the main microprocessor reads software from the memory and performs a self-check. It then reads data from the numerous sensors on the engine and converts them into useful information. This information is often transmitted over the CANbus – your car’s internal computer network – to other electronic modules.

Once the main microprocessor has interpreted this information, it refers to the numeric tables or formulae within the software and activates outputs as required.

Fault Codes

When a fault code is stored in the memory, it usually results in some of the logic within the software being bypassed with reduced engine efficiency, albeit with the engine still being able to function on a basic level. In some circumstances, the self-diagnosis routine discovers a serious fault that either fundamentally prevents the engine from running, or shuts the engine down in the interest of safety.

With modern engine management, the first fault diagnosis step for a vehicle technician is to access fault codes from the ECU memory. These are often stored as 5 digit alphanumeric codes beginning with a P, B, C or a U, followed by 4 numbers.


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