Limp Mode Explained: The Symptoms, Causes, and Diagnosis

Most modern vehicles have a feature called limp mode. This is basically a safety feature for your transmission and engine. As you may know, newer vehicles have engine control units in them. An engine control unit serves as the central computer system which receives information from various other systems and sensory components of a vehicle. If for some reason the engine control unit detects mechanical problems or abnormalities with any of the sensors, it will automatically activate the limp mode.

The purpose of limp mode is to prevent the transmission and engine from going through some major failure as a result of these issues. When the limp mode is activated by the computer, it causes your overall vehicle performance to be reduced. That way, there is less demand placed on the transmission and engine while these other issues are going on with the vehicle. The name “limp” means that your car will move very slowly as you try to get it to the nearest mechanic or your home. If you’re too far away from either one, then use limp mode to pull over safely on the side of the road. Then just call a tow truck to help you out.

Top 3 Symptoms

You should never ignore the symptoms of limp mode. Even though it is meant to protect your transmission and engine, it can only offer this protection for so long before they end up failing. You need to get your car to the mechanic as soon as possible after you notice these symptoms.

1) Slower Speed – As previously indicated, limp mode causes there to be a power reduction in the vehicle. This means your acceleration will be much weaker when you step on the gas pedal. You’ll be lucky to go faster than 35 miles per hour. Don’t take the vehicle on the interstate.

2) Check Engine Warning Light – If you’ve experienced speed reduction, then this will be followed by the check engine warning light activating on the dashboard. Your engine will overheat more when running at a lower speed because the oil cannot circulate through it fast enough. That is why the warning light comes on.

3) Shifting Difficulty – If things have gotten really bad in limp mode, then you won’t even be able to shift gears properly. If you can shift gears, then you probably won’t be able to go higher than third gear.

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Top 3 Causes

Here are the 3 common causes of limp mode.

1) Low Transmission Fluid – A low amount of transmission fluid will reduce the pressure in your transmission. The result is a transmission that cannot work right, which results in limp mode coming on.

2) Wire Damage – Any electrical wire damage in your vehicle will cause the limp mode to activate. Wires can get damaged due to battery acid leakage, too much heat, or accidental debris impact. Whenever you have a damaged wire, the engine control unit will detect a weak electrical signal coming from that area of the vehicle. It will activate limp mode in response.

3) Bad Sensor – There are several important sensors in your vehicle, such as the speed sensors, TPS, MAP, and MAF. If any of these sensors go bad, it’ll cause the limp mode to turn on because the engine control unit won’t receive a good signal from them.

Diagnosis

To figure out the exact cause of the limp mode, a diagnostic scanner needs to be used on the engine control unit. This will retrieve the proper trouble code from the computer and display it on the scanner’s screen. Use the owner’s manual or manufacturer’s website to figure out what a particular trouble code means. You can also have a mechanic determine this for you.

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