|Code||Fault Location||Probable Cause|
|P2564|| Turbocharger (TC) boost control position sensor - circuit low |
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|Wiring short to ground, TC boost control position sensor|
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What Does Code P2564 Mean?
OBD II fault code P2564 is a generic code that is defined as, “Turbocharger Boost Control Position Sensor “A” Circuit Low”, and is set when the PCM (Powertrain Control Module) detects an abnormally low voltage in the turbocharger boost control position sensor’s control and/or signal circuits(s).
Note that this code indicates a failure or malfunction in the electrical circuit(s) of the turbocharger boost control position sensor, and rarely (if ever) involves malfunctions of the turbocharger itself. Also, note that this code is among the most common codes on OBD II compliant vehicles that have turbochargers.
Turbochargers all work in the same way; exhaust gas exiting the engine through the exhaust manifold drives a turbine wheel that then drives a compressor wheel via a shaft that connects the turbine and compressor wheels. The compressor wheel then uses its extremely high rotational speed to compress the intake air, which allows for larger volumes of air and fuel to be forced into the cylinders.
If a turbocharged engine runs at a constant speed, the exhaust gas would exit the engine at a constant speed and volume, and therefore, the turbine wheel would also run at a constant speed, producing a constant boost pressure. However, since car engines do not run at constant speeds, the speed and volume of the exhaust gas they generate also vary greatly, which produces large variations in available boost pressures, which in turn, greatly affects engine performance at some engine speeds.
Moreover, since the action of compressing the intake air has a profound braking effect on the speed of the compressor wheel, the design of the turbine wheels in turbochargers are optimized to extract the maximum amount of energy from exhaust gas exiting the engine at low speeds and volumes. However, the downside of this is that at high engine speeds, the high flow rates and volumes of the exhaust gas that exits the engine can propel the rotating assembly to speeds that could generate boost pressures that could potentially destroy the engine.
Thus, to prevent this from happening, turbochargers on stock engines are matched to the air intake requirements of the engine, but to “smooth out” large variations in boost pressure that result from large changes in engine speed, all turbochargers are fitted with boost control valves, as well as (often) with sensors that detect the position of the boost control mechanism. Here is how this set-up works-
At low engine speeds, the PCM monitors the actual boost pressure via a dedicated boost pressure sensor, and if the actual boost pressure is lower than the desired boost pressure given the current operating conditions, the PCM will command the boost pressure valve closed to utilize all the energy of the exiting exhaust gas. This valve is typically vacuum controlled, but in some applications, electrically controlled stepper motors control this valve.
As the engine speed increases more exhaust gas flowing at ever-increasing rates begins to propel the turbine and compressor wheels to ever-increasing speeds, which generates an ever-increasing boost pressure. Thus, to prevent the boost pressure from increasing to beyond a maximum allowable value, the PCM activates the vacuum (or electrically) controlled boost control valve to allow some exhaust gas to escape directly into the exhaust system without acting on the turbine wheel. The effect of this is two-fold; the reduced exhaust gas flow serves to slow the turbine wheel down, while the braking effect of compressing the intake air further reduces the speed of the rotating assembly, which then reduces the effective boost pressure.
In practice, the PCM monitors the actual boost pressure continuously via the boost pressure sensor, and in a fully functional boost control system, the PCM will open and close the boost pressure control valve continuously in a manner that maintains the effective boost pressure within a predefined range, which is always referenced to the engine speed and load.
For this system to work as both designed and intended, the PCM needs to “know” when the boost control valve is open or closed. Without this data, the PCM can’t control the boost pressure, so the boost control valves of turbochargers on most applications are fitted with position sensors that relay the actual position of the boost control valve to the PCM. Again, in a fully functional boost control system, the PCM compares input data from the boost control valve’s position sensor with input data from the boost pressure sensor (among others), and when both actual values agree with desired values, the PCM will activate the boost control valve to adjust the effective boost pressure to an appropriate value.
However, since the PCM cannot monitor the position of the boost control valve’s position sensor directly, the PCM uses changing voltages in the boost control valve’s position sensor to infer its position. We need not delve into the complexities of this system here, beyond saying that when the boost control valve is in the closed position, the PCM expects to see a pre-defined voltage value, and vice versa; when the valve is in the open position, the PCM also expects to see a predefined voltage in the sensor’s signal circuit.
Therefore, the PCM uses a specified voltage to infer the position of the boost control valve, which voltage is relayed to the PCM via a dedicated signal circuit. It should be noted though that since the resistive element in the boost control valve’s position sensor forms part of this circuit, a failure or malfunction in the position sensor itself could also cause code P2564, or contribute to setting this code.
So in practice, code P2564 does not refer to a failure, malfunction, or defect in the turbocharger itself. This code refers specifically to a fault, failure, or malfunction in the electrical circuits that are directly associated with the boost control valve’s position sensor. Thus, when such a failure occurs, the PCM will recognize that it cannot control the boost pressure effectively and it will set code P2564, and possibly illuminate a warning light, as well.
Where is the P2564 sensor located?
This image shows a boost control valve position sensor from a late-model VW application. In this example, the actual position sensor is indicated by the red arrow, while the sensor’s electrical connector is indicated by the blue arrow. The green arrow indicates the attachment point for the vacuum hose that actuates the boost control valve, while the yellow arrow indicates where the valve connects to the linkage from the actual boost control valve inside the turbocharger casing.
Note that while the actual appearance of boost control valves and their position sensors vary somewhat between applications, most designs follow this general pattern.
Be aware though that not all boost control valves are fitted with position sensors. In some cases, the boost control valve is controlled via pressure from the intake side of the turbocharger.
What are the common causes of code P2564?
The most common causes of code P2564 are largely similar across all applications, and could include one or more of the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and or connectors (Most common)
- Engine vacuum leaks that affect the operation of the boost control valve’s actuator, but note that this will usually (but not always) be indicated by the presence of one or additional air/fuel metering codes
- Defective turbocharger boost control position sensor
- In rare cases, this code can be caused by restrictions in the inlet or exhaust system
- Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any control module is reprogrammed or replaced
What are the symptoms of code P2564?
Common symptoms of code P2564 could include the following-
- Stored trouble code and possibly an illuminated warning light
- In some cases, several additional codes relating to air/fuel metering may be present along with P2564
- Power loss that can vary from slight at certain engine speeds, to severe at all engine speeds
- Fuel consumption may increase considerably
- The engine may hesitate or stumble upon acceleration
- The engine may exhibit misfires or misfire-like symptoms at some engine speeds and loads
- In some cases, severe engine damage may result if the turbocharger’s boost pressure cannot be controlled effectively
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