P0120 Ford 4.9L – How To Test a TPS
The P0120 OBDII trouble code is a throttle position sensor error, specifically regarding the range of the signal being sent. Your throttle position sensor (TPS) tells your Ford Powertrain Control Module (PCM) how much the throttle blade is opened.
Using this data the PCM can control your engine in closed loop to maximize operation as Ford originally designed.Without the proper range of signal voltage being sent to the PCM, operation of the vehicle will be troublesome at best.
The vehicle may buck or bog instead of accelerating or idling as you originally intended. It’s never a good idea to drive or operate a vehicle with any kind of throttle position sensor problems.The specific Ford verbiage for the P0120 OBDII trouble code is Throttle Position Sensor Out of Range. I will be showing you how to test, fix and resolve this issue in a 1996 Ford F-150 4.9L L6 with a VIN ID of Y.
This engine has been around the block for quite some time but in this EFI version of the 300ci 4.9 liter Ford, I will show you how to resolve the P0120 OBDII check engine code.
Symptoms of a Failed TPS
Problems that can arise from your Ford having a throttle position sensor error can range from annoying to dangerous. As stated previously however, if you have a vehicle with an existing throttle position sensor error, it’s probably best to not drive or operate it.
- Inconsistent idle
- Surprise acceleration or deceleration
- Bucking or bogging
- Excessive smoke or emissions
Possible causes of P0120 Throttle Position Sensor Out of Range
- Bad throttle position sensor
- Short or exposed wire in throttle position sensor connector
- Bad grounds or electrical problems
Where is my Ford 4.9L TPS?
The TPS in your 4.9 liter Ford truck engine is located opposite the throttle body butterfly on the throttle body housing. Our Ford F-150 uses a twin intake tube style snorkel led from the airbox mounted to the driver side fenderwell.
To access your TPS you will need to remove the intake snorkel leading from your factory airbox to the throttle body as shown in the image below. The TPS is behind the plastic shield circled in white.
Other possible related Ford Trouble codes
Code 23: Throttle Position Sensor (TPS) Circuit Performance Problem
- Code 53: TPS Circuit High Input
- Code 63: TPS Circuit Low Input
- How To Test your Ford TPS for Power
To conduct these tests, you will not need to unplug the TPS but just backprobe the wires on the TPS connector. This means you will need the ignition set to the ON position but the engine should not be on.The Ford F-150 TPS is a three wire sensor that is fed from the truck’s PCM. There is a switched power circuit, a signal circuit and a low reference circuit or ground.
How to Test the Ford TPS for Power
You will need a multimeter or a DC voltage reading device to begin testing the power and ground signal wires at your Ford TPS. Connect the black lead of your multimeter to the negative terminal of your battery, and backprobe PIN A for a 12 volt switched battery signal. If you are confused which wire is which note the orientation of the slot on the connector below PIN C in the diagram above.
Never use the ground pin or PIN C for testing purposes, as this can damage your PCM or other electrical components of your Ford truck or van.
Still confused? Unplug your TPS connector and the pin identification should be inside the TPS or stamped inside the TPS housing. If power does not exist here, this is a major issue as this power wire is connected to other EFI sensors on your Ford engine. Check your wiring and track back for any possible breaks or shorts, check for exposed wires near the connector.
Now you’ll be checking PIN C for the low reference circuit or the ground of the TPS harness. If you have a ground signal here, your TPS should be receiving the power and ground it needs to operate. Let’s see if your Ford TPS is any good in the next step, or how to check your Ford TPS for Signal.
How To Test your Ford TPS Signal
Here’s where we’ll be checking for the voltage range of your Ford TPS and the trouble code P0120. Because the voltage is out of range, this could be due to damage or wear on the throttle position sensor arms.
Backprobing PIN B on the TPS with the ignition turned to the ON position, manually turn your throttle blade butterfly to see the voltage being sent by the sensor. By turning the throttle body manually you are simulating the same action as depressing the accelerator pedal.
With the throttle blade shut you should have near to one volt of signal being sent on PIN B. Slowly open the throttle blade to see this voltage rise, and it should peak at around 4.5 volts at wide open throttle (WOT).
If your TPS signal is smooth and rises and falls as one would expect, the issue may be intermittent. Try resetting your OBDII check engine light and see if the error returns.
However if you see spikes or dips in voltage or any missing voltage while turning your throttle body, you need a replacement TPS. The part number for this Ford sensor is F2TF-9B989-AA a subdivision of part number E9TF-BA or F2TF-AA. If your local Ford dealer does not have this part number, you can also opt for E9TF-9B989-BA or E9TZ-9B989-B.
Congratulations, you have now resolved your P0120 OBDII check engine code. Please leave me any questions or comments below!
Thanks for reading!