PSA/BMW 1.6T issues – How to diagnose

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PSA/BMW 1.6T issues – How to diagnose

So I’ve gotten quite a few questions from people all over the place about having turbo issues etc.

One thing to keep in mind about these motors is that “limp mode” (when the ECU “disables” the turbo) is not always turbo related. Limp mode is there to protect the engine from damage.

A few (but not all) reasons as to why the car could go into limp mode:

Faulty sparkplugs and/or ignition coil(s)

Fuel pump problem

Vacuum pump problem


Turbo problem

Faulty sensors

Air leaks

In this guide a will touch on a number of reasons as to why the car can go into limp mode; but mainly I will focus on things related directly to the turbo, how to diagnose the issue, and how to solve them. The majority of this text will be my own, but I will also include text and images that has been provided by E-tuners.

A turbo is a great way to get more power out of a car; but when the car goes into limp mode you soon realize how big of a difference that turbo makes. When the problem persists, it can become very frustrating for the owner, not to mention the thousands it will cost to replace the turbo. So to know what to look out for and how to diagnose the system in order to determine if the turbo is in fact in need of replacement is absolutely vital.

In the case of the PSA/BMW 1.6T motor, it is best to become familiar how the turbocharging system works. So first, Let’s get some basic knowledge of it.

How it all fits together

A turbo charger is a very simple device. There are 2 sides to it, the exhaust side, and the compressor side (which is where the incoming “fresh” air goes into the turbo). Each side has a “propeller” and they are connected to each other via a shaft.


When the exhaust gasses start to turn the exhaust propeller, the propeller on the compressor side has to turn too. It is this turning of the propeller at very high speeds that compresses the air. The faster it turns, the more “boost” (compression of air) it creates.

The problem is, that if the amount if compression cannot be controlled, the turbo will just continue adding more and more compression to the incoming air, until the point that the engine cannot handle it anymore; in which case the engine will sustain damage.

So, to control the amount of compression, a “wastegate” is used. A wastegate is simply a valve that directs more or less exhaust gases to the exhaust propeller.

Closed wastegate = more exhaust gas = more compression,

Open wastegate = less exhaust gas = less compression.

There are two types of wastegates, an internal (is part of the turbo) and an external wastegate (separate from the turbo). In the case of this particular turbo, an internal wastegate is used.

Essentially, think of the wastegate as the “accelerator pedal” of the turbo.

A wastegate is still a mechanical part (as is the turbo), but you still need something that will control the wastegate. For this there is an “actuator”.

The actuator is connected to the wastegate via the actuator rod and wastegate arm.


Two nuts on the rod, on either side of the wastegate arm are what hold it in place.


The rod simply pushes (opens the wastegate) or pulls (closes the wastegate). But again, the actuator too is only a mechanical part; so you still need something that can control it.

In the case of this particular turbo, PSA/BMW does things in a bit of an unconventional manner.

Usually it’s the actual boost that acts on the actuator. However, in this case, its vacuum that acts on it. For this vacuum to be generated there is a vacuum pump. Essentially it is the vacuum pump that makes the actuator rod either pull or push the wastegate. However, again, the vacuum pump is also mechanical. So, in between the vacuum pump and actuator comes the Boost Control Valve (BCV).


The BCV is an electronic valve that is connected to the ECU and it is this valve that will determine how much of the vacuum is sent to the actuator, and how much of it will be directed away.

More vacuum = actuator rod pulls = wastegate closes = more boost

Less vacuum = actuator rod pushes = wastegate opens = less boost

The BCV is a very important part of the system because if the vacuum pump was just directly connected to the actuator, the ECU will have no way of controlling the amount of boost produced, and eventually the engine will be damaged.

So that is how the system works at producing boost. But there is still two more essential pieces to the puzzle, the sensors and the diverter valve, and another valve that isn’t generally associated with turbos, but also plays a part in this particular case

There are various sensors that calculate many different things. But for the purposes of this article I will only cover some of them.

There are oxygen sensors that calculate how much oxygen is present, so that the ECU will know how much petrol is needed. Then there is a MAF (Mass Air Flow) sensor and a MAP (Manifold Absolute Pressure) sensor. All of these are simply there to calculate how much air is flowing into the engine and at what pressure the air is, etc. And based on these readings the ECU then calculates how much fuel should be delivered and what kind of boost should be produced.

Next is the Diverter Valve. If the turbo is producing boost, and you take your foot off of the accelerator pedal, there will still be some boost in the intake system. When you take your foot off of the accelerator pedal, the throttle plate closes; so the excess boost has nowhere to go other than back to the turbo. If, at this point, the pressurized air cannot be redirected before it reaches the turbo, it can eventually destroy the turbo. This is because a propeller is aerodynamically designed to only be turned in one direction. If the pressurized air is to enter the turbo while the throttle plate is closed, the air will try and force the compressor propeller to turn in the opposite direction of which it was designed to turn. The reason this can cause turbo damage is because the exhaust gases will be turning the exhaust propeller in the correct direction, but then the unwanted boost will try to turn the compressor propeller in the incorrect direction; which places a huge amount of twisting force on the shaft which connects the two propellers.

So, a mechanism is needed to release this excess boost before it gets to the turbo; which is known as the Diverter Valve (DV). This is sometimes also referred to as a “Blow Off Valve” (BOV). There is, technically, one key difference between the two. Both have the same purpose (to release excess boost when the throttle plate is closed), but a BOV releases the boost to the atmosphere (which gives the loud “PSSSHH” sound associated with turbocharged engines), whereas a DV diverts the excess boost back into the intake pipe (between the air filter and turbo).

And that’s it; that is how the entire system works. Not entirely AS complicated as you might have thought, huh?

Lastly is the Canister Depollution Valve. This is also an electro valve, and is part of the intake manifold pipe. The function of this valve is to be open when boost isn’t needed, and to be closed when boost is needed. When it is open, it allows petrol fumes from the petrol tank to pass through to the intake manifold. If the valve remains open when boost is needed, the boost will be directed to the petrol tank, instead of reaching the intake manifold where it is needed.

Diagnosing problems

So, only now that we have a better understanding of the system as a whole will we know how to test the different components to see where the problem lies.

Diagnostics software

Perhaps the most important part is getting a diagnostics cable. This is to connect to the diagnostics port of the car to find out what error code has caused the car to go into limp mode.

You will need an ELM327 OBD-II usb cable, and some software on a Windows-based laptop.


There is plenty of software out there, but a good and free bit of software to check and clear fault codes is EasyOBD.

When the check engine light comes on, its an indication that there is some sort of malfunction, and the ECU will record a certain code which helps to identify what kind of problem it is. In the case of turbo trouble, the most common codes will be P2622 and P0299, which means “turbocharger underboost” and “turbocharger boost not detected”. There are plenty of other codes that will put the car into limp mode, but these two are the most important in determining whether or not there is a problem with the actual turbo.

Another common fault code is that there is an air leak. In which case you should inspect all the turbo hoses and pipes, and perhaps even the intercooler.

In order to read the fault codes, plug the serial end of the cable in to the diagnostics port of the car and the USB side into the computer. Put the key into the ignition and just turn it to the first click (do not start the engine). Then, on the computer software, click on the button to make a connection with the ECU, and then go into the fault codes section.

Testing the components

We’ll start off with the easy ones and work our way through the entire system. I will break down all the parts into a new section to make it easier to follow.

Diverter Valve

From the factory the diverter valve is manufactured to withstand 1 bar (14 psi) of pressure. On a stock setup this is the pressure that the turbo supplies. However, the blow-off valve still fails. Inside it has a rubber membrane, which at some point will tear. The company that makes the blow-off valve is called Pierburg, and they make blow off valves for VAG (Volkswagen Audi Group) and these blow-off valves can be found in a range of VW, Audi, Skoda and Seat models. The blow-off valve in the VAG cars are manufactured to withstand pressures higher than 1 bar, which makes it perfect for the problem. Now the entire VAG unit will not fit our setup, but all we need are the internals. So, all you need to do is to go to VW and purchase the blow-off valve. Then you just have to swap out the VAG unit's internals with that of the Peugeot's.

In some cases the internals don’t quite work with the stock diverter valve housing. In which case you would have to use the entire VAG unit, and to fit it to the turbo unit. To do this you would have to remove the metal clips in the bolt holes, and also make the bolt holes on the diverter valve slightly larger. I recommend also that you put a small washer between the DV housing and the bolt head to ensure that the bolts hold tight.


Remove the intake pipe that goes to the turbo. Look inside the turbo to see if the propeller blades are still ok.


They should all look the same and have no damage on them. It is normal to sometimes have very SLIGHT damage on one or two blades; but remember that turbo blades need to be perfect to work best.

Turn the propeller. If it cannot turn, it means that the propeller(s) have seized and a new turbo will be needed.

Next, VERY GENTLY try to wiggle the propeller up and down, side to side, in and out. If there is no movement the shaft is still perfectly fine and is another good indication that the turbo does not need replacing.

Actuator rod

In order to inspect the actuator rod, you will need to remove the Oxygen sensor and heatshields to properly see it. Sometimes, the nuts that hold the actuator rod and wastegate arm together come loose or even fall off.

Check to see if the wastegate arm is in the correct place on the actuator rod. The nut closest to the actuator should be 14 complete turns from where the thread ends on the side closest to the actuator.


While the nuts are loose, check the movement of the wastegate arm. You should be able to move it quite easily along the actuator arm. If there is no movement the wastegate is faulty and will require a new turbo.

BE CAREFUL WHEN TIGHTENING THE NUTS AGAIN. Make sure that they are tight, but do not use TOO MUCH force, as this could bend the wastegate arm, and will just add a whole new headache for you.

If all seems well, tighten the nuts and move on to check the movement of the actuator. With your right hand, place your thumb on the actuator, and use your index and middle finger on the round bit on the actuator arm. Move the round bit towards the actuator. There should be roughly 1cm of movement. If there isn’t, either the actuator is faulty and will require a whole new turbo assembly, unless you can get a used actuator from somewhere.

Boost control valve

As I mentioned earlier, PSA/BMW have done the turbocharging thing in a bit of an unconventional manner. Usually when a car is off, the wastegate would be closed, and will open when the car is switched on. In this case, however, the wastegate is open when the car is off, and will close when the car is switched on. A simple way to test the BCV is with a syringe. Pull the piston of the syringe (but don’t pull it completely out). Now, remove the hose from the actuator, and place the syringe nozzle inside of it. When you switch on the car (i.e. let the engine run) the piston should be pulled inwards due to the vacuum. If it does, you automatically know that the BCV and the Vacuum pump are fine. However, if it doesn’t get pulled in, then there is an issue with either one of the two. To figure out which one, you will need some extra vacuum hose. Make sure the car is off and remove the hose that is on the vacuum pump, and attach the one side of your spare vacuum hose to the vacuum pump. Now attach the other side of the hose to the syringe. Again, prepare the syringe in the same manner as you did the first time. Now start the car and see if the syringe’s piston gets pulled inwards. If it does, then the vacuum pump is fine but there is a fault with the BCV. This may be something simple like just the electrical connector that isn’t making proper contact, or the BCV itself needs replacing as the piston inside of it has become stuck.

Vacuum pump

If the syringe does get pulled in, the next test will narrow the issue down to the turbo, or actuator.

Connect the vacuum pump DIRECTLY to the actuator. Then take the car for a drive. When you push the accelerator pedal down, the car should boost up very quickly, and will actually overboost as the ECU has no control over how much boost is produced. Since there is no control, I strongly advise that you do this with caution, and only do it once. If no boost is produced, there is an issue with the actuator or turbo


Lastly would be to have the sensors check. Since the sensors are there to provide the ECU with vital information, if they are faulty and give the ECU the wrong readings, it will cause issues.

I hope this little guide has been helpful, and will aid in solving your issues if you should encounter any.

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