Testing and troubleshooting the throttle position sensor (TPS) on your Ford or Lincoln car, pick up or SUV is an easy thing to do. You don't even need a scan tool to test it. A simple multimeter will suffice and in this article I'll take you thru' the whole diagnostic process step by step.
Below you'll find a list of Ford and Mercury and Lincoln cars, pick ups and SUV this article applies to (although the tests could apply to any Ford vehicle on the road today). Also in this section you'll find the info to make your testing as easy and as uncomplicated as possible.
OK, one last thing before we jump into the article, you can find a complete list of 4.6L and 5.4L ‘How To Test’ articles that are located in this Web Site and at troubleshootmyvehicle.com and this list is found here: Ford 4.6L, 5.4L Index Of Articles.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (Ford 4.6L, 5.4L) (at: autotecnico-online.com).
Symptoms Of A Bad Ford TPS
The most common symptom is the check engine light (CEL) is on (also known as the MIL=Malfunction Indicator Light) on your instrument cluster and annoying the heck out of you as you drive. Among other things, your vehicle might be experiencing:
- TPS diagnostic trouble codes (DTCs) stored in the vehicle's computer's memory.
- P0121: Throttle Position (TP) Circuit Performance Problem.
- P0122: Throttle Position (TP) Circuit Low Input.
- P0123: Throttle Position (TP) Circuit High Input.
- Really bad gas mileage.
- Transmission does not shift out of second gear.
- No power as you accelerate the vehicle.
- Hesitation when you step on the accelerator pedal.
What Tools Do I Need?
As mentioned at the opening of this article, all that you'll need to be able to use the info and perform the tests in this article is a multimeter (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 may need a helper to perform some of these tests.
Circuit Descriptions Of The Ford TPS
As you already may know, the throttle position sensor (TPS) on your Ford (or Mercury or Lincoln) vehicle has three wires coming out of its connector. Below are short descriptions of the signal each one carries. This are the Circuit Descriptions that we'll be using thru' out the rest of the article to test the TPS on your vehicle.
- Circuit labeled 1:
- 5 Volts from PCM.
- Circuit labeled 2:
- Throttle Position (TP) Signal Circuit.
- Circuit labeled 3:
- Sensor Return (Ground) Circuit.
I recommend that when you test for the particular signal in the wire, that you use a tool to pierce the wire, such as a wire-piercing probe (click here so that you can see what one looks like: Wire Piercing Probe). Disconnecting and probing the front of the female terminal of the connector can get you into a lot of trouble, if you open up the terminal with the probe you're using.
One last observation, these three circuits go directly to the PCM. So you need to be careful not to short these wires to power (12 Volts) or you may fry the PCM.
How Does The Ford TPS Work?
Here's some very basic working theory that'll help you to understand the ‘why’ and ‘how’ of the three tests you're gonna' do with the help of this article. OK, in a nutshell, when you crank and start your Ford vehicle:
- The PCM (Powertrain Control Module=Fuel Injection Computer) feeds the throttle position sensor with 5 Volts and a Ground.
- This Ground is known as the Sensor Return in Ford tech speak.
- As you step on the accelerator pedal, the TP sensor translates the amount of throttle plate opening (caused by the accelerator cable) into a voltage signal the PCM can use.
- The PCM uses this voltage signal , that will vary with the amount the throttle opens as you accelerate or decelerate the vehicle, to inject fuel, control ignition timing, and the rest of the song and dance the computer has to do to get your vehicle moving or slowing down.
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, on with the show, go to: TPS TEST 1: Testing The 5 Volt Reference Signal.