What Does Limp Mode Mean & How Do You Fix It?

In this article we will be looking at a warning light known as Limp Mode. We will be explaining what the signs of limp mode are, what might cause it and what you might have to do to resolve it. This protective mode is often seen as a frustration but in actual fact it is very important to your car's health.

What Is Limp Mode?

The obvious place to start is by explaining just what Limp Mode actually is. This is essentially a safety feature of some modern vehicles for the engine and transmission. If either the engine or transmission control units receive an error message from their respective systems limp mode is activated.

Limp mode essentially decreases power and RPMs with the intent of protecting our engines from further damage. An issue has been detected that may be worsened by running the engine at full power so the car's computer limits the engine function to allow you to get somewhere to fix your problem.

In older cars these kinds of problems would be reported to the driver using the check engine light but too often this warning light is dismissed. With the advent of limp mode we now have a system that ensures you take care of the issue.

How Do You Recognize Limp Mode?

It is important to know when your car has entered limp mode because this is a sign that you have an issue that if unresolved may cause further damage to your vehicle. Whereas you could previously ignore the check engine light and cause yourself a big repair bill you now have no option but seek resolution.

Warning Lights

Not all check engine light warnings will coincide with an activation of limp mode but limp mode will be accompanied by a check engine light. If your check engine light illuminates and it is accompanied by your car's version of a limp mode indication this is an obvious sign.

Different car manufacturers have their own versions of limp mode so the warning light will also differ. A common light will depict an engine outline that is half illuminated hinting that the engine is working at half power.

Check engine lights do not always mean you are in limp mode so to be sure look for an accompanying light, other symptoms of limp mode and if possible use an OBD2 scanner tool to diagnose your issues.

Reduced Engine Power

This is a symptom that you are unlikely to miss. If along with the check engine light your car suddenly has a drop in engine power this may be because it has done so in order to prevent further damage. The Engine Control Module (ECM) will have determined the threat of damage warrants limiting the power of the engine.

Engine power can of course drop without actually being in limp mode but if it is not the ECM limiting power then something major has likely broken which has limited the performance of the engine. Essentially the damage is severe enough that the engine can not actually run properly anymore.

Lower RPM Limit

Another sure sign that you may be in limp mode is a sudden limiting of the vehicle's revs. If you are trying to rev the engine but the RPMs do not pass a certain limit this may indicate that the ECM has set a limit in these to protect the engine.

If your RPM gauge will not go beyond 2500 – 3000 RPMs then the engine may be limited. Limp mode is likely active so you are receiving the minimum revs to allow you to safely get your car somewhere that your problem can be repaired.

Gears Will Not Change

With the revs limited it would also follow that your ECM might put a limit on the gears your automatic gearbox can use. High gears will no longer be available and you may not be able to get past third gear.

If your engine power drops, your revs are limited and your gears are locked this is a good indication that your car is in limp mode and things need to be fixed very soon.

What Can Cause Limp Mode to Activate?

Turbo Boost Pressure

You will often find limp mode technology associated with newer turbocharged vehicles although it is also in non-turbo cars as well. A common cause of limp mode however is issues with turbo boost pressure. If the pressure is too high this risks causing damage so the ECM will limit your engine to avoid this possibility.

Limp mode can also be activated because of low pressure or a slower than normal build of pressure. The most common causes of turbo issues are wastegate, boost pressure sensor, boost pipe leak or the boost control valve.

Faulty Engine Sensors

Sometimes there may not be a transmission or engine issue exactly; it might just be that a sensor is no longer working so the information received by the ECM is corrupted. As this information is vital to the smooth running of the engine any deficiency can cause poor performance which can be damaging.

Common sensors which could be at fault causing limp mode include MAF sensor, MAP sensor, engine temperature sensor, boost pressure sensor, or the O2 sensor.

Transmission Problems

This is most common in automatic transmissions whereby limp mode will be activated in the event that a problem is detected in this system. There are no shortage of problems in the transmission that might cause limp mode such as bad shift solenoids, low transmission fluid, faulty sensors, or a control valve issue.

Wiring Issues

The main problem with today's modern cars is ironically the thing that makes them so modern, it’s the electrics. With all these new features there is more and more wiring involved in our vehicles. The numerous electrical parts all need to be connected with wires and of course wires themselves can become damaged or loose over time.

A disconnect in the wiring can cause the ECM problems in running the engine correctly which may result in a limp mode activation. This is often a hard thing to diagnose as there are so many wires in our cars today so it can be a long search and sometimes a difficult repair.

Tips to Fix Limp Mode Issues

Sometimes the issues causing the limp mode activation are simple to repair and may just be a case of better maintenance rather than an expensive repair. This means that you can take a few steps right away to discount a simple to fix problem before delving too deep.

Check Your Car's Fluids

You may get a limp mode issue if your certain car fluids are too low. This might include engine oil, coolant, power steering, transmission and brake fluid levels. You will not only want to check the levels to make sure you have enough but also the quality.

If your engine oil is dark and thick you may need an oil change or if there are signs of fluids mixing you will need to get this resolved. Generally speaking if you find one fluid mixing with another then you have some kind of leak that you will have to fix.

Clean the MAF Sensor

The Mass Airflow (MAF) sensor is a common cause of limp mode and it may be broken. It is however also possible that it has become dirty and may simply need to be cleaned off. As it is involved in allowing air into the engine then dust and dirt from the air can make it dirty and ineffective.

You will need to remove the sensor and carefully clean it with an electronic cleaner. It is a sensitive component however so you should not touch it with a towel or your hands. Refer to a MAF sensor cleaning guide before you attempt this.

Check Air Filters

Your problem may simply be a clogged air filter preventing the engine from getting enough air to operate correctly. Checking the engine air filter is pretty simple as is replacing it. Often at oil change outlets they will check this filter and offer you a new one. This does not need to be done for every oil change but from time to time it is wise to have it replaced.

Check the Trouble Codes

If the problem is not resolved by one of the simple methods already mentioned then you likely have a more serious issue. You can often diagnose this yourself if you have an OBD2 scanner tool. This handheld device can plug into your car via the OBD port which is most likely somewhere below your steering wheel.

The scanner will locate the trouble codes in your car's ECM or transmission control unit to give you an idea of what is actually wrong. More advanced scanners may also offer you repair advice including suitable parts to make replacements with.

Bring in the Pros

If you have reached the end of your technical comfort zone and do not feel like the issue is something you personally can resolve there is no shame in taking the issue to the pros. Sometimes the problem is complicated and needs someone with the appropriate skills to diagnose and fix.

Conclusion

Limp mode may be a frustration but you should trust it, in fact you have no option really. Although the cause may be simple, fixing this engine safety feature is important to prevent you turning a minor issue into an expensive engine repair.

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