OBD-II Code P1120 — What It Means & How to Fix It

What Does This Error Mean?

P1120 means the Throttle Position Sensor (TPS) has an Out of Range Low reading. The throttle position sensor tells the PCM how far open the throttle plate is. When the TPS voltage stays below the minimum expected value at idle or during normal driving, P1120 is triggered. You may feel hesitation on acceleration, rough idle, poor throttle response, or the engine stumbling when you press the gas pedal.

Affected Models

Common in Ford and Mercury vehicles with PCM-monitored TPS circuits
Common in Ford Explorer, Expedition, F-150, and Ranger with 4.0L and 4.6L engines
Common in Mazda vehicles sharing Ford powertrain platforms
Also seen on Toyota, Nissan, and some GM vehicles with standalone TPS sensors

Common Causes

Worn throttle position sensor with a dead spot or low voltage output
Corroded or loose TPS connector causing low signal voltage
Open circuit in the TPS signal wire reducing voltage below minimum
Incorrect TPS base voltage adjustment (on older vehicles with adjustable TPS)
Failed throttle body with a worn TPS mounting surface affecting sensor alignment

How to Fix It

Use a scan tool to monitor TPS voltage at idle and slowly through the throttle range. The voltage should sweep smoothly from approximately 0.5V at idle to 4.5V at wide-open throttle.

Any flat spots, jumps, or voltages stuck at 0V confirm a bad sensor or wiring issue.
Inspect the TPS connector for corrosion, bent pins, and loose fit. Clean with contact cleaner and reseat.

Corroded connectors are especially common on older vehicles and those in high-humidity climates.
On older vehicles with an adjustable TPS, check whether the base voltage is set correctly. Idle voltage should be in the range specified for your vehicle (typically 0.45 to 0.55V).

A misadjusted TPS on an older Ford or Mazda can trigger P1120 even if the sensor itself is fine.
Test the TPS reference voltage (5V) and ground at the connector. No 5V reference means a PCM or wiring fault — not a TPS fault.

The PCM supplies 5V to the sensor and monitors how much comes back through the signal wire based on throttle position.
Replace the TPS if it has a dead spot or outputs an out-of-range voltage. On electronic throttle body vehicles, the TPS is integrated and requires the whole throttle body to be replaced.

After throttle body replacement, perform the idle relearn procedure specified for your vehicle to calibrate the new sensor.

When to Call a Professional

TPS replacement costs $80 to $250 parts and labor. Throttle body service or replacement is $200 to $600. Wiring repair is $100 to $300. On drive-by-wire vehicles, electronic throttle body replacement requires PCM relearn after installation.

Frequently Asked Questions

Is P1120 the same as P0122?

They are related — both indicate a low TPS signal. P0122 is a generic OBD-II code for TPS circuit low. P1120 is a manufacturer-specific code (common on Ford) for TPS out of range low. Both usually have the same root causes and repair steps.

Can a bad TPS cause my car to stall?

Yes — especially if the sensor has a dead spot at the idle position. The PCM momentarily loses track of throttle position and may cut or add fuel incorrectly. This can cause stumbling, hesitation, or stalling at idle or low throttle.

Do I need to calibrate a new TPS after installation?

On older cable-driven throttle bodies, the TPS sometimes needs voltage adjustment after installation. On modern drive-by-wire vehicles, the PCM automatically learns the new sensor's range after an idle relearn procedure. Consult your repair manual for the correct post-installation procedure.