P1120 – Throttle Position Sensor Out of Range (FORD, LINCOLN, MERCURY)

By Reinier (Contact Me)
Last Updated 2019-09-19
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1120

Table of Contents

1. What Does Code P1120 Mean?
2. Where is the P1120 sensor located?
3. What are the common causes of code P1120?
4. What are the symptoms of code P1120?
5. Get Help with P1120

What Does Code P1120 Mean?

OBD II fault code P1120 is a manufacturer specific code that is defined by car maker Ford as “Throttle Position Sensor Out of Range”, and is set when the PCM (Powertrain Control Module) detects that the actual position of the throttle plate does not match the desired position.

Since efficient engine operation depends on accurate control of the throttle plate, all throttle bodies incorporate a sensor whose exclusive function it is to monitor the position of the throttle plate from idling speed to WOT (Wide Open Throttle) conditions.

In terms of operating principles, throttle bodies are for the most part simple potentiometers that are directly linked to the shaft that controls the movement of the throttle plate. In a fully functional system, one end of the resistive strip in the sensor is connected to a reference voltage that is supplied by the PCM, while the sliding part of the sensor is connected to the PCM via a dedicated signal circuit.

In practice, and when the throttle plate is in the closed position, the sliding part of the sensor is close to the point where the reference voltage enters the resistive strip. Therefore, a (relatively) high voltage is passed back the PCM, which interprets the high voltage to mean that the throttle is in the closed position. However, as the throttle is opened, the sliding part of the sensor moves along the resistive strip, which means that progressively less current is fed back to the PCM as a result of the resistance of the resistive strip increasing as the sliding part of the sensor moves away from the reference voltage connection point.

The PCM interprets the constantly changing signal voltages as constant changes in the effective throttle opening, and uses this information to make constant changes to the injector pulse width and ignition timing settings to ensure efficient operation of the engine throughout its operating range. Note though that the PCM does not only monitor the actual opening of the throttle; it also measures the rate at which the throttle opens and closes as one of the parameters that apply to automatic transmission control strategies.

Thus, as a practical matter, the PCM needs to “know” the position of the throttle plate at all times in order to be able to control not only the fuel injectors and ignition timing systems effectively, but also to exercise effective control over the transmission. Therefore, if the PCM detects a condition in which the actual position of the throttle plate does not agree with the desired position, it will set code P1120, and illuminate a warning light. Note that in some cases, and depending on both the application and the exact nature of the problem, the PCM may initiate a fail-safe or limp mode as a safety precaution since it cannot manage engine control functions that depend on the throttle position effectively.

Where is the P1120 sensor located?

The image above shows the location (arrowed) of the throttle position sensor relative to the throttle body on a late model Ford Mustang. On all other Ford applications, the throttle position sensor will also be located directly on the throttle body, although the overall appearance of the throttle body/position sensor assembly may be different from the example shown here.

What are the common causes of code P1120?

It should be noted that the deviation between the actual and desired positions of the throttle plate typically needs to fall into a range of between 3.42 % and 9.85% before this code will set. In practice, these values correspond to 0.17 volts and 0.49 volts both when the ignition is turned on with the engine not running, and when the engine is running at a steady speed.

Nonetheless, some common causes of code P1120 could include one or more of the following-

• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors in the throttle position sensor’s control and/or signal circuits
• Damaged or defective throttle position sensor
• Damaged or defective throttle body/throttle plate
• Poor or incorrect adjustment of the throttle position sensor
• Failure to perform the relevant throttle position relearning procedure after a throttle body replacement
• Use of substandard aftermarket throttle body/throttle position sensor
• Use of incorrect or unsuitable throttle position sensor
• Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced

What are the symptoms of code P1120?

Common symptoms of code P1120 could include one or more of the following-

• Stored trouble code and illuminated warning light
• Engine may exhibit varying degrees of power loss- from slight and barely noticeable, to severe enough to immobilize the vehicle
• Engine may not idle, or idling may be rough, erratic, or fluctuating
• Gear shifts may be harsh and/or unpredictable
• In a large percentage of cases, the PCM may initiate a fail-safe or limp mode as a safety precaution

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