Buying a used ECU could end up being a very costly mistake

Modern vehicles are fitted with a variety of different electronic control units (ECUs for short). These are small devices containing effectively a miniature computer or computers, designed - as the name suggests - to control various functions. The most frequent applications are for engine management and control of systems such as ABS braking and traction control. For many years now, virtually all vehicles have incorporated an engine management computer. However, there can be smaller units (or functions combined into other ECUs) that deal with everything from central locking to even something as minor as the delay function for interior lights or the rate of flashing of turn indicators. As cars have become increasingly complex, the range of ECUs and ECU functions have expanded massively and most now control many different systems.

a typical vehicle ECU

Although generally robust and relatively reliable in most cases, ECUs in vehicles (and particularly any that are positioned in the engine compartment) are subject to notably adverse conditions. Extremes of temperature, vibration and moisture can play havoc with electronic devices and ECU failure is certainly not unknown. In addition, the units are very sensitive electrically. External faults can cause problems. In particular, the old-fashioned process of jump starting a car with a flat battery can cause voltage 'spikes' that can irrevocably damage a number of ECUs throughout a vehicle. For this reason, you should never attempt to jump start any modern vehicle under any circumstances. Although awkward and time-consuming, you should instead disconnect the battery from the car for charging.

As vehicles become older, failure of one or more of the ECUs becomes more of an issue and more commonplace. Replacement units from main agents can be extremely costly and there is naturally a significant temptation to look for a second-hand replacement and fit it yourself. A quick search on the Internet will turn up handfuls of second-hand ECUs for just about every car imaginable. However, it is a false economy and in the vast majority of cases, it will be a complete waste of money, or even worse.

Many electronic control units are software 'one time coded' to work correctly only with the vehicle they were originally fitted to. These units 'recognise' the vehicle's unique codes and details, and all the other devices in the electrical network of the vehicle, and will not work if fitted to a different car. This is frequently because the units interact, so for safety reasons it is vital that they 'know' what other units are incorporated into the car's systems and the precise way they work. It becomes more complicated, as units may differ slightly from month to month as improvements are made and therefore, the way they work may differ between two cars that appear almost identical. If your vehicle is diagnosed as having a faulty ECU, please do not consider buying a second-hand replacement unit. In many cases it will simply not work at all, or may appear to function, but may compromise safety, performance and economy, or the correct operation of other units. Further, in some cases, serious damage could be caused to other units. Please also note that whilst we can 'read', de-code and reprogram some ECUs, this is certainly not always the case and many main units (especially engine management types) cannot be programmed. In many cases, you will have wasted your money completely, and the original faults, or worse, will remain.

However, all is not lost! At MK T and B Centre, we have the most up-to-date equipment and trained technicians. Further, we have excellent contacts with specialist companies. In the vast majority of cases, we can have your original faulty ECU repaired or replaced for a substantially lower cost than a main agent. Even if the worst comes to the worst, we can supply and correctly program new replacements at a significant saving. If you have a problem with an ECU, please contact us first. In the long term, it is almost certain to save you money and a great deal of problems.

follow us on Facebook     click to email us     we are a Which Trusted Trader     see us on Twitter      Find us on Google