Frequently asked questions

Faulty engine management ECUs give rise to common problems such as no start or random stalling. They can also can cause problems with engine warning lights, idle and emission control, cold and hot start also low power and lean running.

Some cars have a design flaw – water ingress if the drainage channels on your bonnet are blocked. This can wet and can damage the ECU.

Is my ECU faulty?

The majority of engine management faults are NOT the engine ECU. Consequently changing the engine ECU will not cure the fault. It is best practice to carefully diagnose what the fault is, paying particular attention to sound connections and good maintenance of components and sensors.
We do not test ECUs. You will find companies that provide a test service. MAKE SURE you are happy with the test service they provide and that it really checks all features of your ECU.

Check numbers match yours.
It is very important to replace like-for-like. If the part numbers are the same, the part will be loaded with identical software and hardware, making sure that it runs your car as the Maker intends.

If part numbers are slightly different, the part may run your vehicle but not as the Maker intended OR it may not run it at all.

What part numbers do I check?

There are usually two or more part numbers on any ECU – the manufacture (eg BOSCH, Siemens, Magneti Marelli, Ford, etc) part number and the car manufacture part number – there may be other numbers as well.

General rules for engine part numbers


Most vehicles earlier than 1995 have immobilisers separate from the engine ECU and do not need to be coded – Plug and Play.

Engine ECUs for vehicles later than 1995 will need to be coded to the engine management system BY A QUALIFIED AUTO ELECTRICIAN

If you buy the ECU on it’s own – it is usually transferrable but will need coding to match your vehicle’s security system. This needs to be done by an auto electrician using the correct software. Even though the ECU is transferable, you must still ensure the replacement ECU part numbers fully match yours.

Coding ensures that the vehicle’s immobiliser recognises the different ECU and will open the ECU to run the vehicle. Coding requires the expertise of a qualified auto electrician using correct software and equipment.

Plug and play sets
You will find on the market either ECUs sold singly or as ECU + transponder; + key + other parts (full set). If you find the full set: ECU (must be correct part numbers) with its transceiver and key (with transponder in) and other parts – you will be able to fully replace with your full set, without further programming of the ECU. But full sets are not always available.


ECUs earlier than 1995 are usually uncoded and may simply be exchanged and will work fully without coding as they are not coded to the car’s security system. You must still ensure that the replacement part numbers fully match yours.

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