Accurately testing the throttle position sensor (TPS) on your Ford 5.0L or 5.8L pickup, van or SUV is not hard to do.
In this ‘How To’ tutorial, I'll show you how to test the TPS with a multimeter and find out if it's really bad or not.
This is an on-car test of the throttle position sensor. You'll notice that the photos show the TPS out of the car, but this is only to make it easier to explain the test.
Contents of this tutorial at a glance:
- Symptoms Of A Bad Throttle Position Sensor.
- What Tools Are Needed To Test The TPS?
- Circuit Descriptions Of The Throttle Position Sensor.
- How Does The Throttle Position Sensor Work?
- TEST 1: Testing The TP Signal With A Multimeter.
- TEST 2: Making Sure The TPS Is Getting 5 Volts.
- TEST 3: Making Sure The TPS Is Getting Ground.
- The TPS Code Won't Go Away.
- Where To Buy The TPS And Save.
- More Ford 5.0L And 5.8L Tutorials.
You can find this tutorial in Spanish here: Cómo Probar el Sensor TPS (Ford 5.0L, 5.8L) (at: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor
The one thing that you can definitely count on, when the TPS fails, is the check engine light shining nice and bright to let you know that there's a Diagnostic Trouble Code stored in the fuel injection computer. Here are some specific symptoms you'll see:
- TPS diagnostic trouble codes (DTCs) stored in the vehicle's computer's memory.
- Code 23: Throttle Position (TP) Circuit Performance Problem.
- Code 53: Throttle Position (TP) Circuit High Input.
- Code 63: Throttle Position (TP) Circuit Low Input.
- Code 121: Throttle Position (TP) Circuit Performance Problem.
- Code 122: Throttle Position (TP) Circuit Low Input.
- Code 123: Throttle Position (TP) Circuit High Input.
- Really bad gas mileage.
- No power as you accelerate the vehicle.
- Hesitation when you step on the accelerator pedal.
There are times when the ECM (Electronic Control Module = Fuel Injection Computer) will think the TPS has failed when it hasn't. This usually happens when the ECM spits out several diagnostic trouble codes at once and so what will save you time, money and the frustration of replacing good parts, is to test the throttle position sensor.
What Tools Are Needed To Test The TPS?
The most important tool you'll need is a multimeter. The multimeter can be an analog or digital one (don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing).
You'll also need:
- A helper.
- Wire piercing probes
- Since the TPS has to be tested in action (and with the Key On), you'll need to pierce the wires with something to get to the signal inside the wire.
- To see what a wire piercing probe looks like, click here: Wire Piercing Probe.
A generic scan tool that can read OBD I diagnostic trouble codes does come in handy, but the scan tool won't help you test the TPS and therefore you won't need it to use the test info in this tutorial (the test in this tutorial will help you test the TPS without a scan tool).
Circuit Descriptions Of The Throttle Position Sensor
Below are the job descriptions of the three wires that stick out of the TPS:
- Circuit labeled 1:
- 5 Volts from PCM.
- This wire is Red in color.
- Circuit labeled 2:
- Throttle Position (TP) Signal Circuit.
- This wire is Black in color.
- Circuit labeled 3:
- Sensor Ground Circuit.
- This wire is Green in color.
You'll need to keep one very important thing in mind and that's that these three circuits go directly to the ECM. So you need to be careful not to short these wires to power (12 Volts) or you will fry the fuel injection computer.
How Does The Throttle Position Sensor Work?
The TP sensor's job is to inform the ECM how much the throttle plate is opening or closing. It's able to do this because it's mounted on the throttle body and directly linked to the throttle plate shaft. So when the throttle plate shaft rotates, a wiper inside the TPS also moves (along a curved resistor) and is able to send a variable voltage signal to the ECM.
OK, in a nutshell, when you crank and start your Ford vehicle:
- The throttle position sensor gets 5 Volts and Ground from the ECM.
- As the engine in your pickup or van idles (and the throttle plate is closed), the throttle position sensor sends the ECM a voltage signal of about 0.9 to 1 Volts.
- Once you step on the accelerator pedal, the throttle plate opens and since the TPS is connected to the throttle, it starts to measure how much it opens.
- When the throttle plate opens, the voltage increases. When the throttle plate closes, the voltage decreases.
- The ECM is then fed this changing voltage.
- Once the PCM gets this voltage, it does its little song and dance and starts to calculate fuel injection, ignition timing, transmission shift points, etc. in conjunction with the MAP sensor, PIP sensor, engine coolant sensor and so on and on.
- This process of informing the ECM of throttle plate angle goes on the whole time the engine is running.
Pretty simple stuff, no? Well testing it is just as simple. Since you'll be working in the engine compartment, no need to tell you (but I'm gonna' tell you anyway) to be alert and be very careful. Use common sense and take all necessary safety precautions. OK, let's get this show on the road, go to: TEST 1: Testing The TP Signal With A Multimeter.