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What Is Limp Home Mode?

Limp home mode (more commonly known as just limp mode) is a really strange thing and is something that more and more modern car manufacturers have started including in cars. You may have experienced it before yourself. You're driving along and all of a sudden your car has low power, won't go over 40km/h or won't change gears.

But why is this so? Is there any purpose to limp mode?

Well, to start out you have to know that in older cars a lot of the driving responsibility was left up to the owner.

In fact, up until recently cars where much simpler devices and a driver could fairly easily keep and eye on the temperature gauge, oil pressure gauge and battery voltage while still keeping an eye and ear out for strange happenings in the engine bay.

However, even though it was easier, it still didn't prevent all issues. If there was a problem brewing deeper in the engine, there wasn't always a way to tell which meant that breakdowns where still pretty common.

The first attempt at something like limp home mode was actually the engine light.

These systems were around for a long time and are a simple but effective way of letting the driver know there was a problem. However, with the advent of computers in cars, these warning lights really began to take off.

What does this have to do with limp mode though?

Well it's really quite simple. The automotive industry started with gauges and moved to engine lights as a way to inform a driver of an issue and limp mode is just an extension of the engine light and a way to prevent further damage.

See, while it was fairly easy to recognise signs of engine trouble in older cars, a lot of new cars are far more complex. Between interference engine designs, electronic engine control, emissions control and the hundreds of sensors needed to just get a car running, noticing a problem in a new car using just gauges would give a NASA scientist a terrible headache.

Because of this, any time a modern car suspects a significant issue, it will use the engine computer to reduce the engine power, reduce the top speed of the vehicle and do anything it can to help keep the powertrain in good condition.

So why have limp home mode at all? If a problem is that significant, why not just shut the engine down completely?

Here's where it gets interesting. Even if the engine is in danger, manufacturers have to put your safety first. If you're on a highway and the engine just shuts down or, if it's late at night and you're far away from civilisation, having a car that doesn't go at all puts you in a much more dangerous situation.

Realistically, limp home mode does exactly what is says on the box. It's not a way for you to continue to drive the car but, it is a way to allow you to get home or get to safety even if the engine has a problem.

What are some of the issues that cause limp home mode? It definitely varies from car to car but, some of the causes include blocked DPF's and exhaust components, heavy misfiring, a failing sensor, timing faults and much more.


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