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Your Throttle Position Sensor worn out? » Read more about common malfunctions • Repair • Replacement manual
Most important reading device for the control unit: the throttle valve potentiometer
The throttle valve potentiometer is a sensor positioned in the intake manifold of the car. It measures the angle position of the throttle valves. If it fails, the car usually switches into failsafe mode. With a bit of luck, the throttle valve potentiometer can be repaired. In most cases, replacement is necessary. Fortunately this is not difficult.
How much fuel does the engine need?
Cars with combustion engines drive on an air-fuel mix. The control unit regulates the injection of the fuel in the engine's combustion chamber. The driver signals his intended speed to the control unit via the accelerator pedal. By doing so he adjusts the angle of the throttle valve, controlling the amount of air that is added. The angle position is registered by the throttle valve potentiometer and its value is transmitted to the control unit. This allows calculation of the exact fuel amount to be pumped into the combustion chambers by the injector nozzles.
Throttle valve potentiometer: construction and location
Essentially, a throttle valve potentiometer is a simple component. The potential is measured along two calibration distances. Depending on the position of the throttle valve this distance is longer or shorter, which changes the resistance in the line. This resistance change is converted into a measured value and transmitted to the control unit. The redundant (double) layout is a safety feature: as a rule a defect never occurs simultaneously on the two calibration distances. The control unit always measures the value of both distances. If the discrepancy is too large, the control unit initiates the fail-safe mode and issues an error message. The throttle valve sensor is located sideways on the throttle valve. This is located in the intake manifold where it connects with the intake pipe.
Throttle valve sensor defects
The first warning signal of a failing throttle valve sensor is an irregular, jerky engine running. A reluctant throttle response can also indicate a defective component. The most explicit response is the engine switching into fail-safe mode. Depending on the car it can only be driven at a speed between 30 and 100 km/h. Reading the error memory makes the diagnosis definite.
Throttle valve sensor repair
A throttle valve sensor can fail as a result of pollution. This regularly occurs in diesel engines with exhaust recirculation. The recirculated exhaust gas can strongly affect the throttle valve as well as the connected sensor. This particularly occurs when the seal between sensor and valve is no longer fully intact. Penetrating oil and soot in the sensor and the plug connection impair its functionality. If this occurs, the repair of the component can be attempted by thorough cleaning. Most suitable is brake cleaner with its strong degreasing effect. Subsequently, depending on the sensor's size, the electronic system should be checked. It often has cold soldering joints which can be repaired by careful soldering. However, this should only be attempted by experienced DIY'ers. When the throttle valve potentiometer's functionality has been restored, it should completely be checked. The resistance values can be obtained from the manufacturer or by consulting the repair manual. Now, the sensor is installed again and the error memory deleted. All potential causes for the failure have to be eliminated. This particularly applies to the gasket between sensor and throttle valve. If you do not trust yourself to repair the sensor, the only option is replacement by a new component.
Buying a throttle valve potentiometer
The price of a sensor strongly depends on the car in which it is installed. The price range varies greatly. For a Peugeot 106 the spare part is available at 15 EUR (± £13). A BOSCH throttle valve sensor for Volkswagen or Audi on the other hand, can easily cost more than 200 EUR (± £180). In case of expensive spare parts, a repair attempt makes sense. When the replacement sensor for a compact car is cheap, it is better to save yourself the trouble: everything which is offered cheaply, can usually not adequately be repaired. All in all, the diagnosis "defective throttle valve sensor" may sound ominous. Once all contexts are understood, the repair is not really that complicated.