Car Care: The key to unlocking your car

Make the testing of all coded keys part of any pre-purchase inspection. Photo / iStockphoto

Immobiliser system can leave you marooned if you are not careful

If you own a reasonably late-model vehicle, chances are it is fitted with an engine immobiliser -- an anti-theft system which stops a vehicle from being hot-wired, the engine being started and the vehicle driven away once a break-in has occurred.

There are a couple of important ingredients to the immobiliser system: the ignition key itself (or an attached key fob) and the vehicle's on-board electronic control unit (ECU). Both units are specifically linked to each other by way of a unique electronic code and, when matched, allow the engine to start.

For owners it's an anti-theft deterrent but it can cause a lot of grief and become a very expensive experience if the immobiliser key is lost or damaged.

For obvious security reasons an owner cannot just simply go and buy another key over the counter and expect to automatically start his/her vehicle. There is a re-learning process that must match the new key with the ECU.

Systems have changed over the years and become less complicated for those with the authority and knowledge to supply a new key and carry out the relearn task, but it's still not a five-minute or cheap job.

So the bottom line is: it's best to have a spare programmed key tucked away somewhere to help dig yourself out of a hole if required.

Which raises the question: do you know where yours is, or, more importantly, do you have one?

It's not uncommon for used vehicles to be sold with only one ignition key, which, in the excitement of purchase, can be totally overlooked, or an assumption made that it's only a key and a spare can be quickly sourced at minimal cost.

It's also not unheard of for a spare key to be provided that unlocks the doors and fits the ignition barrel only, and is not programmed (and not able to be programmed) to allow the engine to fire.

Using the golden rule of "never assume or believe everything you are told by a seller", it's always wise to check all available ignition keys as part of a pre-purchase inspection and negotiate the sale accordingly if they don't all fire the engine. And that's only after you have made a phone call to a locksmith or franchise dealer to check replacement costs.

A spare key that only opens doors can be handy to have but it can also become a nightmare if not marked or used appropriately. It reduces cost to have this type of key hidden somewhere on the exterior of a vehicle (or in your wallet/handbag), if it has, in the past, self-locked for some unexplained reason (yes, it does happen at times) and the keys are left lying in the centre console.

And it helps stop instant panic if children are left in a closed vehicle with the keys within easy reach and they happen to push the lock button.

But be warned: adding that key to the immobiliser key ring is a disaster waiting to happen. The key will enter the ignition barrel and the engine will turn over but not fire so an owner can quickly assume it's an engine and not a key problem. An unsuspecting mechanic can also assume the same thing and spend horrendous amounts of time and money trying to locate and fix an electronic fault that doesn't exist.

And just to prove it can and does happen, I was caught out not so long ago when jumping back into a company-owned vehicle after a fuel top-up. The ignition key I used to crank the engine would not allow it to start.

It was only after several deep breaths and a comparison with the genuine key on the same ring that I realised what was going on.

So the simple old ignition key has changed over the years and while it makes a vehicle a lot less likely to be stolen, it needs to be handled with care and makes having a spare tucked away far more important.

Go find yours before you forget.