P1120
ChryslerThrottle Position Sensor (TPS) output voltage out of expected range for engine operating conditions.
Medium SeverityThis code means the Throttle Position Sensor isn't giving the engine's computer a signal that falls within its expected operational values. This unreliable signal can cause the engine to misinterpret how much throttle you are applying, leading to drivability issues.
⚠️ Before You Begin (Safety First)
Always remember, before you touch anything electrical, disconnect the battery's negative terminal to prevent accidental shorts or unexpected engine responses. Be aware that an erratic throttle signal can cause sudden changes in engine speed, so exercise caution when driving or working near the engine.
Common Symptoms
- Check Engine Light illuminated
- Hesitation or stumble during acceleration
- Rough or erratic idle
- Engine surging at steady throttle
- Difficulty shifting gears (automatic transmissions)
- Vehicle may enter 'limp mode'
Common Causes
- Faulty Throttle Position Sensor (worn internal components)
- Corroded or damaged wiring harness to the TPS
- Poor electrical connection at the TPS connector
- Problem with the Powertrain Control Module (PCM) (less common)
- Throttle body issues (sticky throttle plate affecting TPS position)
Frequently reported on: Chrysler Sebring 2001, Dodge Stratus 2003, Jeep Grand Cherokee 1999, Dodge Ram 1500 2000
Diagnostic Steps
- First, we always start by visually inspecting the TPS and its wiring harness for any obvious damage, frayed wires, or corrosion. Make sure the connector is securely seated.
- Next, you'll want to check for any vacuum leaks around the throttle body, as this can sometimes indirectly affect how the TPS behaves or how the engine interprets its signal.
- Now, let's get out the multimeter. We're going to test the TPS sensor's voltage output. With the key on, engine off, backprobe the signal wire. As you slowly open the throttle by hand, you should see the voltage smoothly increase from a low reading (around 0.5V) to a high reading (around 4.5V). Any drops, jumps, or dead spots indicate a bad sensor.
- If the sensor tests bad, the next step is to replace the Throttle Position Sensor. Remember to often mark its position before removal if it's adjustable, or ensure it's properly indexed if it's a fixed type.
- After replacement, clear the P1120 code using your scan tool and then perform a short test drive to confirm the repair. Pay attention to how the engine responds to throttle input.
👨🔧 When to Call a Professional
If you've checked the wiring and replaced the sensor, and the problem persists, or if you're not comfortable using a multimeter to test voltage, then it's time to consult a professional diagnostician. They can look at live data streams and advanced electrical tests to pinpoint the real issue.
Commonly Asked Questions
What does 'out of range' mean for the TPS?
Think of the TPS like a volume knob. 'Out of range' means the computer isn't getting a signal that makes sense. It might be stuck too high, too low, or sending a garbled signal that doesn't correspond to how far the throttle plate is actually open. The computer knows what values to expect, and if it sees something outside those boundaries, it sets this code.
Can I drive with a P1120 code?
While you might be able to, it's generally not a good idea for long. The engine's computer is struggling to understand your throttle input, which can lead to unpredictable acceleration, stalling, or the vehicle going into 'limp mode' to protect itself. This makes driving unsafe and can potentially cause further issues.
Is replacing the TPS a difficult job?
For most Chrysler vehicles, replacing the Throttle Position Sensor is a relatively straightforward job for someone with basic mechanical skills. It usually involves disconnecting a few bolts and an electrical connector. The trickiest part is often confirming the new sensor is functioning correctly, which is why testing with a multimeter is important before and after.
Does a P1120 always mean the TPS is bad?
Not always, but it's the most common culprit. Remember our visual inspection and multimeter tests? Sometimes, it could be a wiring issue, corrosion in the connector, or even a problem within the Powertrain Control Module itself. That's why we don't just throw parts at it; we diagnose.
How does the TPS affect shifting in an automatic transmission?
That's a good question! The transmission control module (TCM) often uses the TPS signal to understand how much throttle you're giving the engine. This input is crucial for determining the correct shift points and transmission pressure. If the TPS signal is unreliable, the TCM might get confused, leading to harsh shifts, delayed shifts, or staying in a lower gear too long.