|Code||Fault Location||Probable Cause|
|P2261|| Turbocharger (TC) bypass valve/supercharger (8C) bypass valve |
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What Does Code P2261 Mean?
OBD II fault code P2261 is a generic trouble code that is defined as, “Turbocharger (TC) bypass valve/supercharger (8C) bypass valve”, or sometimes as “Turbocharger/Supercharger Bypass Valve – Mechanical”, and is set when the PCM (Powertrain Control Module) detects an abnormal signal or reading in the circuits that control the turbocharger/supercharger bypass valve.
NOTE #1: Turbocharger or supercharger bypass valves go by several different names, the most common being “blow-off valve”, “wastegate”, “dump valve”, “boost control valve”, and “diverter valve”.
NOTE #2: Despite the difference in wording, both definitions given above refer to the same issue, which is a probable mechanical failure of the by-pass valve on either a turbocharger or a supercharger, depending on which forced-induction method is employed on the affected vehicle. In practice, bypass valves on turbochargers work differently from those on superchargers, but in both cases, code P2261 refers to a mechanical failure of the valve, as opposed to an electrical fault in one or more control and/or signal circuits associated with the bypass valve.
The function of forced induction with either a supercharger or turbocharger is to compress the intake air so that more air can be forced into the cylinder as compared to a normally aspirated engine with the same displacement. As a practical matter, the larger volume of air that can be forced into the cylinders allows for more fuel to be added to the air, and the combination of more air more fuel is the mechanism that allows an engine with forced induction to develop greatly more power than a naturally aspirated engine with the same displacement.
We need not delve into the inner workings of turbo-, and superchargers here, beyond saying that superchargers are typically driven by the engine with a drive belt, while turbochargers are typically driven by the engine’s exhaust gas as it exits the engine. Nonetheless, as a general rule, both types of forced induction devices develop relatively low boost pressures*at low engine speeds, and progressively higher boost pressures as the engine speed increases.
* “Boost pressure” is the difference between ambient air pressure, and the pressure that the forced induction device develops at any given engine speed. Note that this increase is not directly proportional to engine speed; actual, and maximum allowed boost pressures depend on the device, the engine design, the engine’s displacement, the design parameters of the forced induction device itself, and in many cases, the type, and quality of the fuel used.
If we assume that a forced induction engine is running at a constant speed, and the boost control system is fully functional, the boost pressure will be relatively constant, and the engine management system will adapt the fuel delivery and ignition timing strategies to suit the current boost pressure to keep the engine working at peak efficiency.
However, both turbochargers and superchargers develop boost pressure with parts that rotate at very high speeds. So if the engine speed suddenly decreases when the throttle is closed, the momentum of the rotating assemblies will continue to develop boost pressures that could easily exceed the maximum allowable boost pressure for that engine at that moment- even if the maximum allowable boost pressure is exceeded only momentarily. This is commonly known as an “over boost” condition, and on many engines, this could cause severe, and even fatal engine damage.
To prevent these conditions from arising, all forced induction devices are equipped with valves or other mechanisms that vent sudden pressure spikes either into the exhaust system or into the atmosphere. Some valves use simple spring tension to keep them closed, which must be overcome by boost pressure to open, while others are controlled either electrically or by a vacuum actuator. In the latter two cases, the PCM will typically monitor the actual boost pressure via a dedicated boost pressure sensor, and based on the data relayed by this sensor, the PCM will command the valve open to dump excess pressure, or to close to contain the boost pressure. In this way, the PCM can maintain the boost pressure at optimal values throughout the engine’s operating range.
In all boost control systems that are controlled by the PCM, the PCM monitors the boost pressure continuously via dedicated feedback or signal circuits, and when it detects an abnormal electrical value in any circuit that is associated with the boost control system, it will set one or more appropriate fault codes. However, in some cases, the PCM may be unable to identify the cause of the problem, especially in cases where the bypass valve is vacuum operated. In such cases, the PCM is programmed to conclude that a mechanical failure (as opposed to an electrical short circuit or open circuit being present) of the bypass valve had occurred. When this happens, the PCM will recognize that it cannot control the boost pressure effectively, and it will set code P2261 and illuminate a warning light as a result.
Note that in some cases, the PCM may also initiate a fail-safe or limp mode that will severely limit the engine speed to protect the engine against damage. The limp mode will typically persist until the fault had been found and corrected.
Where is the P2261 sensor located?
The above image shows an example of a vacuum-operated bypass valve on a fixed geometry turbocharger. In practice though, the appearance, location, and mode of operation of bypass valves vary greatly between applications. In this example, the valve is shown attached directly to the turbocharger casing, with the yellow arrow indicating the vacuum actuator, and the green arrow indicating the mechanical linkage between the actuator and the actual valve, which is located inside the turbocharger.
In other designs, the bypass valve may be located in the boost side of the intake ducting away from the turbocharger. On superchargers, the bypass valve is typically located inside the supercharger’s casing, and it is therefore not readily visible from outside of the supercharger.
Note that despite differences in the location, appearance, mode of operation, and terminology used by different manufacturers, all bypass valves perform the same function, which is to relieve excess boost pressure from the intake system. However, since bypass valves vary greatly in appearance and location, reliable service information for the affected vehicle must be consulted to locate and identify the valve correctly.
What are the common causes of code P2261?
The most common causes of code P2261 are largely similar across all applications but note that in many cases, some likely or probable causes might not appear to be linked to, or associated with the boost control system in ways that are immediately apparent. Nonetheless, some common and known causes of code P2261 on most applications could include one or more of the following-
- Mechanical failure of the bypass valve/dump valve/wastegate/blow-off valve
- Defective or malfunctioning boost control sensor
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Engine vacuum leaks or leaks in the boost control actuator’s vacuum system
- Turbocharger failure
- Supercharger failure
- Exhaust manifold leaks
- Dirty or clogged air filter
- Defective or malfunctioning MAF or MAP sensor(s)
- Clogged or leaking intercooler or boost (intake) ducting
What are the symptoms of code P2261?
Most common symptoms are largely similar across all applications, and could include one or more of the following-
- Stored trouble code and an illuminated warning light
- The vehicle may be in a fail-safe or limp mode
- Multiple additional trouble codes may be present along with P2261, depending on both vehicle and the nature of the problem
- Various degrees of power loss may be present
- Spark plugs may become fouled with oil or carbon deposits
- The engine may emit knocking sounds upon acceleration
- Abnormally low or high boost pressures may be present at different points in the engine’s operating range, depending on the nature of the problem
- Acceleration may be extremely poor
- The engine may run roughly or exhibit misfires at some engine speeds
- The engine may overheat, but note that on vehicles with automatic transmissions, abnormally high engine temperatures almost always cause abnormally high transmission temperatures
- Gearshifts may be harsh or unpredictable
- Fuel consumption may increase dramatically
- Depending on both the vehicle and the nature of the problem, the vehicle may emit excessive amounts of black, blue, or white smoke
- If the vehicle is fitted with a supercharger, excessive boost pressures can cause the drive belt to break, or to shear teeth off of the drive belt