P1120
BMWThrottle position sensor out of range
High SeverityThe Engine Control Module (ECM) is detecting a signal voltage from the throttle position sensor that falls outside its programmed acceptable operating parameters. This means the ECM cannot accurately determine the precise angle of the throttle plate, leading to incorrect calculations for fuel delivery and ignition timing.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is in Park or Neutral with the parking brake engaged when performing any diagnostic work. Disconnect the battery before manipulating electrical connectors or components to prevent accidental shorts or damage to sensitive electronics. Be aware that an erratic throttle signal can cause unpredictable engine behavior or sudden power loss during operation.
Common Symptoms
- Erratic idle speed
- Poor or delayed throttle response
- Hesitation or stumbling during acceleration
- Vehicle entering 'limp home' mode with reduced power
- Check Engine Light illuminated
- Automatic transmission shifting abnormalities
Common Causes
- Faulty or worn throttle position sensor (TPS)
- Open circuit, short circuit, or high resistance in the TPS signal wire
- Corroded or loose electrical connection at the TPS connector
- Loss of 5-volt reference voltage or ground at the TPS
- Less commonly, an internal fault within the Engine Control Module (ECM)
Frequently reported on: BMW E46 325i (2001-2005), BMW E39 530i (2001-2003), BMW E53 X5 3.0i (2001-2006), BMW E38 740i (1999-2001)
Diagnostic Steps
- Connect a BMW-compatible scan tool to confirm the P1120 code and check for any related diagnostic trouble codes.
- Visually inspect the throttle body and the throttle position sensor for any obvious damage, loose connections, or corrosion at the electrical connector.
- With the ignition ON but the engine OFF, use a multimeter to back-probe the TPS connector to measure the signal voltage while slowly opening and closing the throttle by hand. Look for smooth, consistent voltage changes, typically from around 0.5V at closed throttle to 4.5V at wide open throttle. Anomalies like sudden drops, spikes, or static voltage indicate a problem.
- Check the 5-volt reference voltage and ground supply at the TPS connector. Ensure the ECM is providing the necessary power and a good ground connection.
- If the signal voltage is erratic or consistently out of the specified range and the power/ground are correct, replace the throttle position sensor.
- After replacement, clear the diagnostic trouble code with your scan tool and perform a test drive to confirm the repair and monitor real-time TPS PID data for proper operation.
👨🔧 When to Call a Professional
If your methodical voltage checks confirm a stable 5V reference and ground, and the wiring harness shows proper continuity, yet the new throttle position sensor still results in an out-of-range signal, then further investigation of the ECM's internal circuits or communication network is warranted by a professional. This suggests the issue may extend beyond typical sensor or wiring faults.
Commonly Asked Questions
Why would the ECM interpret the TPS signal as 'out of range'?
The ECM has a finely tuned expectation for the voltage signal it receives from the throttle position sensor at every given throttle plate angle. If the voltage transmitted by the sensor deviates from this learned 'map' by a significant margin, or if it suddenly drops or spikes, the ECM flags it as 'out of range' because it cannot confidently calculate the airflow characteristics needed for precise combustion control.
Can this code indicate a problem with the throttle body itself, not just the sensor?
Yes, it absolutely can. While P1120 primarily points to the sensor's signal, a physically sticking or binding throttle plate can prevent the TPS from reaching its expected closed or wide-open voltage. Always manually operate the throttle to ensure smooth, unhindered movement before condemning the sensor itself.
How critical is the TPS signal for engine operation?
The TPS signal is one of the most fundamental inputs for the ECM. It dictates engine load, driver demand for acceleration, and is crucial for calculating fuel injection pulse width, ignition timing, and even automatic transmission shift points. An inaccurate signal can lead to a cascade of drivability issues and significantly reduce engine efficiency.
Is it possible for a wiring issue to cause this code without the sensor being bad?
Absolutely. A frayed wire causing an intermittent open circuit, a short to ground or voltage, or even a high-resistance connection at the sensor plug can corrupt the signal before it reaches the ECM. These electrical anomalies will mimic a faulty sensor, causing the ECM to see an 'out of range' condition. Thorough harness inspection and continuity checks are vital.