Turbo overboost limp mode causes and solutions

Limp mode is often present when you are pressing the gas pedal suddenly, often when you are up a hill, passing others, and the car suddenly seems to lose all power.

Power is immediately restored when you stop the engine and then start it again. In this stage, the ECU (electronic control unit) has sensed that the turbo has created too much boost and the ECU shuts it off and goes into what is called “safe mode”.

There are three common codes for clean mode:

Flashing Boost Deviation:

Flashing Boost Deviation means that you most likely have a vacuum leak somewhere. Check all plastic pipes, actuators, and fittings.

Negative Boost Deviation:

Negative Boost Deviation means that you have a clogged intake, an actuator that leaks, used vacuum hoses, or a sticky turbo.

Boost Positive Deviation:

Increasing the positive deviation means you have a solenoid that is bad/not working properly, the actuator locked/broken, the vacuum hose worn, or a sticky turbo.

Diagnosing and fixing limp mode

This is an overview of how to diagnose and correct clean mode due to a turbo overboost.

There are many different reasons why the engine might overload, some being very simple to check and repair and others requiring more complex repairs. Most overrides are created by

  • Defective or malfunctioning air flow meter
  • Leaks in the vacuum system
  • Bad solenoid valve or not working properly
  • Locked/broken turbo actuator
  • The turbocharger has blocked or has sticky valves

This problem can occur due to improper maintenance of the car or only driving in crowded rads at low speeds.

If it only happens occasionally, go on a long road and try to speed up the car to obtain the limp mode. This will help later to see if the issue is resolved when you try again under similar circumstances.

Bad or failing air flow meter

It’s one of the easiest to check, but you’ll get a Check Engine Light. All you have to do is unplug the air-flow meter and take a test drive. If the power is improved, replace it.

Vacuum leakage

Most problems with the turbo are simple leaks in the vacuum hoses. It is difficult to see on the covered hoses which is the one with the cause, so the simplest is to replace them all, you need about 7 meters of hose.

Check the thickness of the hoses before buying, usually, there are 2 types of hoses, one thinner and one thicker, for the simplest replacement is to directly replace the hose removed so as not to mistake the paths of each of them, which can cause other problems.

Also, check the large vacuum line on the brake booster if you have encountered any difficult brake pedal situation that is likely to be responsible. Make sure that the hose at the bottom of the airbox is connected as well, this is usually overlooked.

If you have not replaced the hoses and you think you have excluded a leak, start checking again, as this is the most common reason for most overheating situations.

The upper line of the solenoid valve is the place where the irregular vacuum is drawn. The vacuum adjustment is drawn by the line greater than 5 mm identified by “output”. The 5 mm line, opposite to the other lines, is the ventilation channel that supplies the line regulated at atmospheric pressure.

Even if the solenoid valve is good, if it does not have a solid vacuum that reaches it, it will not properly send the vacuum to the “out” port just below the empty port. It is also important that the air is clear. It is on the same side of the valve as the connector.

Testing options:

  1. Disconnect the “empty” hose. Connect a strong aspirant to the hose. Start the car. You should get > 25 vacuum.
  2. Connect a vacuum hose directly from the rigid suction pipe of the braking system to the “vac” port on the solenoid valve. You will get an EGR code, but your turbo will work great.

Bad or failing solenoid valve

The solenoid valve adjusts the blades on the turbo. In your car, it will be on the protective wall. It has a gray tip and some vacuum lines attached to it. If it doesn’t work, then you will have an excessive situation.

You can also check if the solenoid is working and move the actuator on the turbo. It’s a little more difficult. Remove the engine cover … use a mirror and a flashlight and watch or feel the actuator as another person puts the key in the ignition. It should move and come back.

An OBD tester is very useful because you can ask the computer to run the solenoid while watching the actuator.

Failing or broken actuator

If this does not work, then you either have a bad actuator or valves stuck in the turbo. If you can get your hands on a vacuum pump, attach it to the drive and see if it is in a vacuum. If you do not buy a new actuator.

As a tip: recondition/clean the turbo and with the actuator replaced in a specialized center, the actuator must be adjusted on the turbine in operation which can be very difficult.

Joining the turbine valves

The actuator activates the turbine valves, and if they are stuck or blocked, they will be locked closed or open, if this is your problem, remove the turbo and clean it. It is not always necessary to replace it.

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