Cars go in limp mode when the On-Board Diagnostic (OBD) system detects a critical problem. The main function of limp mode is to prevent further damage to the engine or transmission.
Limp mode reduces engine output, limits the RPMs and speed, prevents the transmission from shifting gears. Limp mode allows you to reach up to 40 mph speeds.
Limp mode is also called "emergency mode" or "limp home mode".
Common symptoms of limp mode include:
- Reduced power
- Speed limited to 40 MPH
- Engine revolutions limited to 2000 or 3000 RPM
- Transmission won't change gears (Stuck in 2nd or 3rd)
- Very slow response when pressing the gas pedal
Check engine light on or flashing
Engine may overheat
If your vehicle goes into limp mode, don't ignore the problem.
Read the trouble codes with an All System OBD-II scanner as soon as possible. You can read the codes yourself with an OBD-II scanner or have your dealer or mechanic do this for you.
Both the Engine Control Unit (also known as ECU, PCM, ECM) and Transmission Control Unit (also known as TCU, TCM) can force a vehicle to get stuck in limp mode.
- Engine Control Unit fault codes can be read with a generic OBD-II scanner.
- Transmission Control Unit fault codes can be read and cleared with a multi-system OBD-II scanner. Generic scanners and code readers can only read ECU codes but not transmission codes.
An option that won't cost you money is to stop at auto parts stores (Autozone, Advance Auto Parts, PepBoys) and have them read the codes free of charge.
How to Get Out of Limp Mode
The following methods may help you temporarily get your vehicle out of limp mode.
1. Restart Engine
If your vehicle goes in limp mode while driving, find a safe place to stop and restart the engine.
Allow the car to stay completly off for at least one minute before you restart it.
In many cases, this will reset the limp mode and allow the vehicle to operate normally. If the limp mode happens again, you should get your vehicle diagnosed with an OBD-II scanner as soon as possible.
If your engine overheats, allow it to cool down before you restart it.
2. Check Transmission Fluid Level
One of the most common issues that cause limp mode is low transmission fluid. If your vehicle has a dipstick for the transmission, check the oil level.
The procedure for checking the transmission fluid level is not the same as the check engine oil level.
Follow the instructions in your owner's manual to learn how to complete this step. You may have to drive the vehicle to warm up the transmission fluid before you can check the level.
3. Clear fault codes from Transmission Module
If restarting the engine or correcting the fluid level does not fix the problem, your next step would be to read and clear the codes with an OBD-II scanner.
Get the vehicle diagnosed by a professional mechanic especially if the problem returns.
The limp mode can be caused by a lot of different issues and sensors. For example, the limp mode can be caused by a dirty MAF sensor which takes 15 minutes to replace.
On the other hand, it could be an indication of a more serious problem such as a blown head gasket or transmission failure.
There is no need to panic though.
If your check engine light is on, use a multi-system OBD-II scanner such as Launch Creader to read the fault codes from Engine and Transmission modules.
Write down the codes that show on your scanners such as P0300 or P0720 and do further research to understand what causes them.
Let's take a look at the most common problems that cause limp mode.
Transmission Fluid Level
One of the most common problems that put a vehicle in limp mode is the low transmission fluid level.
If your vehicle goes in limp mode intermittently but then drives fine if you restart the car, check the transmission fluid level.
When you drive and your transmission fluid level is low the transmission oil pump may run dry especially during hard accelerations or sharp turns. As soon as the transmission control module (TCU) detects that there is low fluid, it will put the vehicle in limp mode to prevent further damage to the automatic transmission.
Worn spark plugs are another issue that often causes limp mode. In addition to the vehicle going into limp mode, your check engine light may stay on or flash. The engine will run rough and in case of a misfire, the engine may shake.
A bad spark plug (or in some cases an ignition coil) causes what is known as a misfire where one of the cylinders stops working. Bad MAF sensor or clogged catalytic converter can also cause engine misfire.
Driving a vehicle where one or more of the cylinders are not firing, causes damage to the catalytic converter and can cause the engine to overheat.
Mass Air Flow Sensor
The mass airflow sensor is also known as the MAF sensor detects the volume and temperature of the air entering the engine. These parameters are very critical for the normal operation of the engine.
Dirt build-up on the MAF sensors can prevent it from functioning correctly. A dirty mass airflow sensor may send a 1.0 voltage reading to the ECU instead of 5.0 volts when the engine is idling.
To find out why your car is in limp mode read the trouble codes with an OBD-II scanner.
Other possible problems that can put your car in limp mode include:
- Transmission valve body
- Overboots or under boost ( Turbo engines )
- Faulty engine sensors
- Damaged wire harness
- Ground connection
- Low battery voltage
- ABS or Brake system issues
- Wheel speed sensor
- Manifold absolute pressure (MAP) sensor
- Throttle position sensor (TPS)
- Engine overheating
- ECU needs calibration
- Car accident
- Blown fuse for critical vehicle systems
- If water gets on an engine sensor for example after a car wash.
Will Driving In Limp Mode Damage Car
Driving in limp mode for an extended time can cause damage to the vehicle.
Most manufacturers recommend that you ONLY continue to drive a vehicle in limp mode to take it to the nearest mechanic or home.
Do not drive in limp mode if:
- engine is overheating
- oil light is on
- temperature light is on
- check engine light is flashing
- there is noise from the engine or transmission
Driving in limp mode can be dangerous. If you decide to continue to drive, monitor the engine temperature ensuring the engine doesn't overheat.
Operating a vehicle for an extended time in limp mode is unsafe and can cause unnecessary damage to your vehicle.
Your speed will be limited to 30 mph or a max of 45mph. If your car is stuck in limp mode considering taking other routes than driving on the highway.
Why does my car go in limp mode intermittently or when I accelerate?
Common problem that causes your car to go into limp mode when accelerating are low transmission fluid level. Another issue on turbo engine is over or under boost.
My car is in limp mode but no codes are present
Limp mode can be set by the Engine Control Unit (ECU) or the Transmission Control Module (TCM). A generic OBD-II scanner can only read the codes form the engine control unit. Your vehicle may have a transmission issue which means you need a Transmission Scanner to diagnose. Another issue is that your scanner may not be able to read fault codes that are manufacturer specific.
Will driving in limp mode damage my car engine?
It depends on the issue. If your vehicle is overheating pull over and allow the engine to cool down. Other problems such as a bad MAF sensor will put the car in limp mode but are unlikely to cause damage in short term.
Will P21DD cause limp mode?
P21DD means that reductant tank heater (DEF Heater) is defective. Your vehicle will go into limp mode. If you try to reset the codes, they will return the next morning when you start the car.
Will DPF regeneration happen in limp mode?
No. DPF regenertion will not happen in limp mode unless manually forced by a professional diagnostic scanner.
Will disconnecting the battery reset limp mode?
Sometimes. If the limp mode is set by the ECU, disconnecting the battery may reset limp mode. Limp mode will most likly return as soon as you start to drive or once the enigne warms up. If limp mode is set by the transmission module, disconnecting the battery won't reset the limp mode.
Will EGR delete cause limp mode?
Deleting EGR valve can result in excessive carbon build up at the turbocharger over time. Eventually, the VNT mechanism can get clogged which will cause â€œlimp modeâ€.
Will a bad oxygen sensor cause limp mode?
Oxygen sensors do NOT usually cause limp mode.
Will low oil cause limp mode?
Engine oil does not trigger limp mode. At least in most cars. If your oil light is on, you should stop and turn off the engine even if the car does not go in limp mode. Check the engine oil level. Only drive if oil light goes off. On the other hand, low transmission fluid will trigger limp mode.
Can DPF casue limp mode?
A clogged Diesel Particulate Filter (DPF) can and will trigger the limp mode.
Can you bypass limp mode?
You can't bypass limp mode, but you can restart the car as that will often get the car out of limp mode.