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What does it mean when your car goes into Limp Mode?
In this day in age, most systems in your vehicle are electroniclly controlled by computers. Limp Mode or sometimes called Fail Conditions comes into play when the vehicle computer has detected a problem with one of the major
systems within its logic computer.

A reading from any sensor, and the ECU computer knows that the readings are outside of the correct ranges. The
module can’t process the correct outputs based on the data it has. When this happens the vehicle’s
ECU computer will create a trouble code and turn on a check engine or other malfunction indicator light.

Symptoms of Limp Mode

  • None or slow acceleration
  • The intake could be blocked with carbon
  • Speed is restricted
  • Sticking turbo vanes or actuator
  • Exhaust leak could cause the car to enter Limp Mode

Moving the car to a safe place
 The whole idea of Limp Mode was designed to allow the driver of the vehicle to move the car to a safe place,
off a busy road or onto the hard shoulder on a motorway. In some cases the car is still available to drive,
although maybe not to the full potential. Allowing you to drive the vehicle home or back to a local garage for a diagnosis
.
 

Next Step
If your car has entered Limp Mode, when you have arrived at a safe place you may be able to shut down the
vehicle, waiting a few minutes before starting the vehicle up again. In some cases, this resets the electronic
controls, restoring the data. Although the car may run like normal it is still advised to get your vehicle checked
out by a local mechanic for a check as the original fault may not of disappeared. If the vehicle does not reset,
you will need to take the vehicle to a local mechanic for a complete test and diagnosis.


Overboost

Over Boost can be caused for many reasons, the most common ones are listed (below)

Possible Cause(s)

Solution

Air Leak Fine the leak, and replace/
repair pipe/gaskets
Turbo internals may be damaged Diagnose and Repair / Replace Turbo
Foreign Matter (Impact) may of entered the inlet pipe Replace the Turbocharger
VNT Blocked Replace and Repair Turbo
Actuator settings may be wrong Replace Actuator

Low Boost 
When the engine lacks power or has low boost there can be a variety of possible causes for this. Check
the possible causes (below) and then match it to the solution.

Possible Cause(s)

Solution

Internal Engine Components Worn Repair the Engine / Replace worn parts 
Air Filter Blocked Replace the Air Filter
Turbo internals may be damaged Diagnose and Repair /
Replace Turbocharger
Air pipe (to the turbo) is restricted Replace the Air Pipe
VNT Blocked Replace / Repair Turbo
Airleak Find the leak and replace/
repair pipe/gaskets
Actuator Arm is Stuck Open Replace Actuator
Sticking Vanes

VNT Turbo Vanes have replaced the original and older type of wastegate system on most diesel
turbochargers. The reason being to improve fuel economy, to reduce emissions and to make the turbocharger
more responsive even at low speeds.

Turbo Vanes are a row of vanes fitted inside the the turbocharger which will match the boost required from the
engine at low engine RPM. The VNT Turbo Vanes will close thereby giving a rapid boost and response time.
They also lower the LAG prone to the wastegate type turbochargers. When the engine is running at higher
revs the VNT turbo vanes open to maximize exhaust flow, to avoid over-speeding or over-boosting and
damaging the turbochargers or even the engine.

Turbo vanes VNT Vacuum Turbo Actuators