P1120 Ford 4.6L – Test a Crown Victoria TPS

The P1120 Ford OBDII check engine trouble code has to do with the throttle position sensor in your Ford Crown Victoria. This sedan is widely used and recognized as being used by peace officers as their main means of transport, and today I’ll be showing you how to test the throttle position sensor in a 1999 Ford Crown Victoria with a 4.6 liter engine. The sensor that is causing the problem in your 4.6 liter Ford is primarily responsible for telling your Ford PCM of how far the throttle is opened.

The TPS is a potentiometer style device that reads the basic position of your throttle blade, and transmits this information to your PCM. Your Ford computer then  uses this signal as well as other engine references to run and operate your engine. Without the throttle position signal, your Ford PCM will have a hard time operating the V8 engine in your Crown Victoria.


The specific wording for the P1120 Ford is Throttle Position Sensor Out of Range, which means that the signal is far too low or too high for your Ford PCM to reference. This three wire Ford TPS sensor is made up of a switched power source, a low reference ground signal as well as the signal wire. This guide will be showing you how to test the signal wire on your 4.6 liter Ford engine and find out what exactly is being transmitted to your PCM.

Common causes of the P1120 Check Engine Light

  • Bad throttle position sensor
  • Miscalibrated throttle sensor
  • Faulty Nitrous switch install
  • Wiring problem

As we’ll be testing just the signal wire for your 4.6 liter TPS sensor, you will not need to remove or unplug your Crown Victoria TPS. Instead you will need to backpin your TPS connector, by using a paperclip inserted into the back of the connector. This ensures that your sensor is plugged in and working as the manufacturer intended, while you can test the signal wire being transmitted in the TPS wiring connector.

How To Test a Crown Victoria TPS Sensor

To test your Crown Vic TPS sensor, you will need to locate it and insert the backpin we mentioned earlier. Your TPS sensor is mounted to the throttle body, and under your 4.6 liter Ford engine cover. Once you are ready to test your throttle sensor, reference the image below to take a look at the Ford wiring diagram.


There’s three different colored wires leading out of the Ford Crown Victoria throttle sensor, from left to right and A to C matching the image above, these wires are; BROWN / WHITE – GRAY / WHITE – GRAY – RED. For the P1120 Ford trouble code, the wire you will want to test is the GRAY / RED wire or PIN C. This is the signal wire for your Ford Crown Victoria, and you’ll be testing the output of this wire using your multimeter.

To begin, have a buddy get into the car and turn your ignition key to the “ON” position, but without starting the engine. This powers all electronic sensors in your engine bay, and allows you to easily test your engine and TPS safely.

Testing the TPS Signal Wire

The TPS in your 4.6 liter Ford engine works by reading the position of your throttle blade, and here’s how the part works. When you depress the gas pedal, the throttle cable that runs to your throttle body butterfly opens your throttle plate and allows fresh air to rush into your intake manifold. The pivot and mechanism of the sensor and how it reads the throttle plate is what we are focusing on here, so with the key turned to the “ON” position measure the voltage at PIN C.

With the throttle body in the closed position, you should see a voltage range here between .2 to .9 Volts DC. Now ask your friend to slowly and gently depress the gas pedal, make sure your Crown Victoria engine has not been turned on. While your friend is depressing the gas pedal, you should see the voltage uptick in a corresponding manner until finally topping out at 4.8 volts at wide open throttle (WOT).

If you have this range of voltage coming out of the sensor, this is not a good sign for your P1120 Ford trouble code. This means that your issue lies elsewhere, either a short or break in the TPS connector wiring is causing your problem, or your Ford ECU is dying. If the voltage falls outside of this range, you now realize that your Ford TPS is bad and must be replaced so that you can clear your P1120 check engine code.

The replacement Ford TPS is part number TPS245 for the aftermarket unit, and although you can technically source this part without the throttle body, that’s not recommended for people who aren’t mechanically inclined. Instead replace your entire throttle body to make the process behind fixing your P1120 Ford trouble code much easier.

Have any questions about this guide? Leave a comment below and let me know!

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