Jumpstarting your car incorrectly is one of the most common ways to damage an ECU.

When a car's electronic control unit - 'the computer' - needs to be repaired or, more often, replaced the result is often a hefty bill; an ECU is a very powerful control system capable of monitoring hundreds of channels of information to control every aspect of your car's engine management, as well as other important functions such as handling characteristics, braking systems and climate control.

Les McMaster, chairman of the Motor Industry Workshop Association, explained that if you compare a car engine to a human body, the pistons might be the heart, the headlights would be the eyes, and the ECU would be the brain, controlling a series of actuators to make sure things are running smoothly within the engine.

A number of sensors in the engine bay provide the ECU with maintenance information, and it uses these readings to adjust the engine actuators for optimum efficiency.

But McMaster pointed out: "Many drivers don't realised they can contribute to the premature failure of their cars' ECU by not sticking to a couple of simple rules.

"Jump-starting your car incorrectly is one of the most common ways to damage an ECU."

He advised: "Be very aware of the polarity of the jumper leads when jump-starting a vehicle with a flat battery - many ECU's have been damaged by short-circuiting the jumper leads.

"Always connect the leads positive to positive and negative to negative; most carmakers fit overvoltage protector devices these days, but it can still do damage in the split second before the fuse in the system blows.

"Always connect the positive leads of both batteries first, then the negative leads. This will 'soften' the flow of power through the earthing system and prevent power surges or spikes.


"Don't connect the jump leads with the key in the ignition; insert the key only after the leads have been connected. Connecting the leads with the key in the ignition may corrupt the coding between the key and the ECU. In some cases that's irreversible, which could cost you a new key or a new ECU - or both.

"If you're sitting with a flat battery and you're not sure how to jump start the car, call your your nearest accredited workshop; they'll be happy to walk you through the proper jump starting procedures."