P1120
SubaruThrottle position sensor out of range
Medium SeverityThis code means your Subaru's Engine Control Module (ECM) isn't getting the right signal from the throttle position sensor, which tells it how much you're pressing the gas pedal. When this sensor is out of range, the ECM struggles to accurately control the fuel and air mix, impacting how the engine runs.
⚠️ Before You Begin (Safety First)
Always remember to disconnect the battery before working on electrical components to prevent accidental shorts or shocks. Be careful around moving engine parts and hot surfaces. Wear eye protection when performing any repairs.
Common Symptoms
- Check Engine Light illuminated
- Rough idle or stalling
- Hesitation or surge during acceleration
- Poor fuel economy
- Engine may enter 'limp mode'
Common Causes
- Faulty Throttle Position Sensor (TPS)
- Corroded or damaged wiring harness to the TPS
- Loose or dirty electrical connector at the TPS
- ECM internal failure (less common)
- Issues with the throttle body itself preventing proper TPS movement
Frequently reported on: Subaru Impreza 2000-2005, Subaru Forester 2000-2005, Subaru Legacy 2000-2005, Subaru Outback 2000-2005
Diagnostic Steps
- First, you'll want to visually inspect the throttle position sensor and its wiring for any obvious damage, frayed wires, or loose connections. This is our basic sanity check for external issues.
- Next, let's test the TPS. With the key on but engine off, use a multimeter to check the voltage signal from the TPS. You're looking for a smooth, increasing voltage as you slowly open the throttle by hand. Any sudden drops or spikes tell us there's an issue internally with the sensor itself.
- If the sensor signal is erratic, carefully clean the electrical connector with an appropriate electrical contact cleaner. Sometimes, just a bit of corrosion or dirt can cause these 'out of range' signals. Reconnect it securely, making sure it clicks into place.
- If cleaning doesn't help and the sensor's voltage output is still incorrect, you'll need to replace the throttle position sensor. Make sure to get one specifically for your Subaru model, as they aren't always universal and can vary in design.
- After replacement, clear the trouble code from the ECM using an OBD-II scanner. Then, start the engine and let it idle to see if the symptoms are gone and the code stays away. Always re-check your work to ensure everything is operating correctly!
👨🔧 When to Call a Professional
If after checking the wiring and the sensor itself, you're still getting this code, or if the symptoms are severe and affect safe driving, it's time to consult a professional technician. They have specialized diagnostic tools to pinpoint more complex electrical issues, like internal ECM problems.
Commonly Asked Questions
What exactly does 'out of range' mean for the TPS?
Good question! It means the voltage signal the TPS is sending to the Engine Control Module (ECM) is either too high or too low compared to what the ECM expects for a given throttle position. The ECM has a specific operating window, and if the signal falls outside that, it knows something is wrong and sets this code.
Can I drive with a P1120 code?
While you might be able to, it's really not recommended for long. The engine's behavior can be unpredictable, leading to rough idling, sudden acceleration, or stalling. This isn't just annoying; it can be unsafe, especially in traffic. Plus, running rich or lean can damage other components like your catalytic converter over time, so it's best to address it promptly.
Is adjusting the TPS an option?
Some older TPS units might have had slight adjustability, but most modern Subaru sensors are designed to be a direct replacement and don't require manual calibration. The ECM will learn the new sensor's parameters. If you're trying to adjust it, you might be looking at the wrong kind of sensor or throttle body assembly, or misinterpreting the repair process.
How do I know if it's the TPS or the wiring?
That's a key diagnostic step, and it's why we use the multimeter. If the sensor itself shows a smooth, correct voltage sweep when disconnected from the harness and supplied with proper power and ground, but the ECM is still reading it wrong, then the problem is likely in the wiring harness between the TPS and the ECM. If the sensor output itself is bad, then the sensor is the issue.