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What Happened to Throttle-Position Sensors?

Counterman
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Counterman

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As modern cars and light trucks continue to grow in complexity, their maintenance needs are changing. Component failures that were commonplace just a decade or two ago are becoming much less common today.

An example of this is the throttle-position sensor (TPS). This small plastic sensor would be mounted on the throttle body, usually on the opposite of the throttle cable. The TPS was used to tell the engine control unit (ECU) what angle the throttle body was being opened to by the driver, and the ECU would adjust the fuel as needed based on this data as well as other inputs.

A faulty TPS reading can cause a number of drivability concerns, including:

• Unexplained bucking or jerking of the engine

• Surging engine idle

• Engine stalling, stumbling or hesitation

These sensors were rather inexpensive and usually pretty easy to replace. They didn’t fail too often, but I can remember having to replace them on a few of my own vehicles, as well as some customer vehicles. So what happened to throttle-position sensors, and why don’t we see them as often today?

Throttle-By-Wire

Throttle-by-wire technology has been called by many names, but it operates on a simple principle – an electronic throttle body is used to meter the air entering the engine. This electronic throttle body is controlled by the ECU based on a number of inputs including accelerator-pedal position, mass airflow, manifold air pressure, wheel speed and more. But the important thing to understand is that there is no longer a mechanical link between the accelerator pedal under the dashboard and the throttle body on the engine. So why is this important?

By decoupling the accelerator pedal from the throttle body, automakers are able to precisely control the throttle angle in all operating conditions to maximize throttle response and traction, reduce emissions and improve fuel economy. Throttle-by-wire systems are able to maximize the benefits of variable-valve timing and direct fuel injection by precisely controlling how much air is introduced to the engine.

With the advent of throttle-by-wire systems, we’ve seen a change in how the ECU measures the throttle position. The TPS still is being used today, but it’s now incorporated into the electronic throttle body. In fact, some electronic throttle bodies may contain more than one TPS. By using multiple sensors, the ECU can monitor and compare both sensor inputs. Redundancy in electronic systems can be a very good thing.

We’ll talk more about the pros and cons of throttle-by-wire a little bit later, but the fact that the TPS is now incorporated into the electronic throttle body can be a big drawback down the road. You see, it means that the system is now less serviceable than it was in the past. If a TPS failed on a cable-driven throttle body, you could replace the sensor for around $30 to $40 and be back on the road. If a TPS fails inside an electronic throttle body, now you have to replace the entire unit, and that could cost hundreds of dollars.

Then, after the electronic throttle body has been replaced, you’ll need to perform a “relearn procedure” so the ECU can learn how the new throttle body reacts to input, and where the internal mechanical stops are located. Failing to perform this critical step can cause a number of drivability concerns, and a costly customer comeback.

There has been a trend in the automotive space for quite some time now where components are becoming more and more “modular.” When I say “modular,” I really mean “pre-assembled.” After all, vehicles are engineered to go down the assembly line as fast as possible. They’re not engineered to be easy to work on. So it makes sense that automakers would get creative with incorporating certain components together into a modular assembly that can be installed more quickly. Of course, the major drawback with this idea is that the replacement costs are increased, and that cost will eventually fall onto the vehicle owner once the warranty period expires.

Advantages & Disadvantages of Throttle-By-Wire

Throttle-by-wire systems offer a number of advantages. They contain fewer moving parts, so that means less maintenance and lower overall vehicle weight. Their precision allows for improved fuel economy and reduced tailpipe emissions, as well as a better overall driving experience for the typical driver. Finally, the throttle body can be used to help the traction or stability control regain vehicle control.

These systems also have a few drawbacks. They’re more expensive to develop, manufacture and replace. They’re more complex due to the wiring and electronic control units that are used. Some drivers may complain about a time delay or “lag” in engine response after they change their accelerator-pedal input.

Finally, they’re harder to service for technicians. Sure, there aren’t any cables or linkage points to grease or maintain, but the real difficulty lies in the electronic controls. Complex wiring and communication systems are needed in order to control the electronic throttle body and related systems. There also are special procedures that must be followed whenever servicing the electronic throttle body. If an electronic throttle body is replaced, the relearn procedure must be performed. This has a profound effect on engine performance, drivability and idle quality.

If you find yourself selling a replacement electronic throttle body to a customer, there are a few questions you should be asking. Do they have a scan tool that’s capable of bi-directional control? A simple code reader won’t work here. They need the real thing in order to relearn the new electronic throttle body. Many electronic throttle bodies are installed in plastic intake manifolds, so it’s a good idea to sell them a new throttle-body seal as well. Finally, it’s a good idea to check with the customer to see if they’ve inspected the wiring harness and connections for any signs of rubbing, fraying or other issues. These sorts of problems can come back to bite them later on down the road.

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      link hidden, please login to viewand link hidden, please login to viewrefractometers but they both work on the same idea. Simply place a few sample drops of coolant in the tool. For the analog refractometer you then look through the eyepiece and read the inside gauge. For the digital refractometer you just have to push a button and the reading will be displayed on the screen. You will need to read the instructions and be familiar with the tool to understand what the results of each one means to the specific gravity of your coolant. Testing Engine Coolant Condition
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      Knowing how to test coolant temp sensor output is a bit more technical. You will need a multimeter to read the resistance of the coolant temp sensor during the test. You will also need to remove the coolant temp sensor from your vehicle, so refer to a repair manual for the specific procedure. For sensor range testing you will need a container of ice water and a container of boiling water. Finally you need the factory sensor range specifications (usually found in the repair manual) along with a pen and paper to take notes.
      Once you have the sensor out of the vehicle attach it to the connections on the multimeter. Most sensors have two connections and since you are testing resistance, it does not matter which order is used. If your sensor has more than two connections refer to a vehicle wiring diagram to find the ground connection and the voltage input connection. 
      You will be testing engine coolant temperature sensor resistance output in cold water and hot water, then comparing the two readings to the factory specification found in your repair manual. Check the temperature of the ice water to make sure it is as close to freezing as possible (32 degrees F or 0 degrees C). Set the voltmeter to the 20,000 ohm range. Dip the tip of the sensor in the cold water and observe the reading on the multimeter. When the reading stops changing, write it down on the paper as the cold reading. Repeat the same process with the boiling water, being careful to hold the sensor with tongs or similar tool to reduce the chance of touching the boiling water. Write down the hot temperature reading from the multimeter. 
      Now you can compare the two voltage readings to the factory sensor specifications. If the readings are not within specifications the sensor is bad and should be replaced. Now that you know the steps for how to test an engine coolant temperature sensor, you can decide if it is worth your time or if the sensor is cheap enough to just replace it and move on.
      How To Pressure Test A Coolant System
      Luckily learning how to pressure test coolant system components is pretty easy. You will need an
      link hidden, please login to view which looks like a bicycle tire pump attached to a universal radiator cap. Start with a cool engine (never work on a hot engine cooling system under pressure). Remove the radiator cap or coolant reservoir cap if so equipped. Attach the pressure tester to the same place where you just removed the radiator cap or reservoir cap. The pressure tester may have a universal rubber fitting or come with an array of adapters to connect with your particular cooling system. Now use the pump to add pressurized air to the cooling system. Watch the pressure gauge on the pressure tester and add roughly 15 psi of pressure (but no more than that). The pressure gauge should hold steady indicating no leaks. If the pressure gauge goes down or does not register any pressure, double check your pressure tester connection just in case. If the system will not hold pressure, you will need to repair the leak. You can use link hidden, please login to view to help locate the leak if it is not easily apparent. Check out all the
      link hidden, please login to view available on link hidden, please login to view or trust one of our 17,000 link hidden, please login to view for routine maintenance and repairs. For more information on how to test engine coolant sensor output and other cooling system parts, chat with a knowledgeable expert at your link hidden, please login to view. The post
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