FixMyCar explains everything you need to know about limp mode.
Modern cars contain many safety features that run in the background. Most of the time, you hardly notice them, and you don’t necessarily need to know how they work - traction control and the anti-lock braking system (ABS) are good examples.
However, when it comes to limp mode - a lesser-known safety function - there are several things it's beneficial to know as a driver. Read on to find out more.
Contents
What is limp mode?
Symptoms of limp mode
Limp mode causes
What to do if your car goes into limp mode
How long can you drive a car in limp mode?
How to reset limp mode
How to bypass limp mode
How to disable limp mode permanently
What is limp mode?
Limp mode is a safety feature triggered when your car’s engine control unit (ECU) detects a fault. It reacts to this by limiting the car’s power, allowing it to limp home (hence the name) at a much slower speed to prevent further harm.
Essentially, limp mode is a form of damage control. It’s your car’s way of protecting itself - that’s why it should never be ignored when it happens.
Symptoms of limp mode
When your car goes into limp mode, you may notice:
Loss of power
Engine management light
Revs limited to around 2,000-3,000 RPM
Locked to a low gear (in automatic cars)
Auxiliary functions may stop working (e.g. heating and aircon)
Limp mode causes
Many things can cause limp mode, such as:
Transmission faults - when the gearbox can’t switch between gears properly
Malfunctioning sensors - incorrect information is sent to the ECU
Bad wiring - issues in the wiring loom can cause erratic behaviour detected by the ECU
Brake malfunctions - a hydraulic leak or seized brakes
Engine issues - turbo problems or misfiring
Low fluid levels - insufficient engine oil, transmission fluid or coolant
What sensors can cause limp mode?
Examples of sensors that can trigger limp mode include the mass air flow sensor (MAF), throttle position sensor (TPS) and manifold pressure sensor (MPS).
Can faulty glow plugs cause limp mode?
You may see the glow plug warning light while your car is in limp mode. However, this does not necessarily mean the glow plugs are causing your car’s lack of power.This guide discusses what happens when your glow plugs fail.
Particularly in Skoda, Vauxhall and Peugeot models, problems with the diesel particulate filter (DPF) can trigger the glow plug warning light. In this situation, the DPF, rather than the glow plugs, is causing limp mode.
Find out the difference between glow plugs and spark plugs.
What to do if your car goes into limp mode
Limp mode is designed to let you get home after your car suffers a problem - that’s why it’s sometimes called ‘limp home mode’. You can continue to your destination or a garage, but if possible, it’s best to keep driving to a minimum until the issue is resolved.
Check your car’s fluid levels and look for any leaks beneath the vehicle. If low fluid is activating limp mode, this is easy to fix. Failing that, the best thing to do is take your car to a garage or contact a mobile mechanic to find out what has triggered limp mode.
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How long can you drive a car in limp mode?
Limp mode isn’t intended to let you keep driving indefinitely because this would be unsafe. Instead, it allows you to reach your destination (if it’s relatively close), find a safe place to stop or go to a garage where you can get help.
Driving further than that puts the health of your car at risk and could end up causing more damage. It would help if you looked at the problem the other way around - rather than asking how far you can drive, think about how soon you can stop driving for the benefit of your vehicle.
How to reset limp mode
Sometimes, limp mode can be triggered by a temporary glitch, so the first thing to do is try resetting it by switching your car off, waiting 30 seconds, and switching it back on again.
If the problem persists, booking a diagnostic test is best. Limp mode isn’t a pointless feature - its purpose is to alert you to a problem. You should only try to reset or bypass it if you know a glitch is causing it.
Book a diagnostic test
How to bypass limp mode
The most obvious way to bypass limp mode is to fix the faulty component causing it. You can also attempt to bypass it by restarting your car or removing one of the battery terminals to reset the system.
If you decide to try the latter option, wait five minutes after disconnecting the battery, then use an OBD scanner to try to clear any faults. Doing this isn’t a guaranteed fix; if a component needs replacing, the ECU will detect it and trigger limp mode again.
How to disable limp mode permanently
You should not try to disable limp mode permanently. It performs a vital function in keeping your vehicle safe. Although it’s inconvenient when triggered, it’s less inconvenient than a broken car requiring expensive repairs.
If you want your car to stop going into limp mode, you should take it to a mechanic who can fix the problem.
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