Throttle Position Sensor Circuit Malfunction
The P0120 code indicates a malfunction in the throttle position sensor (TPS) circuit, specifically sensor A. The TPS is a potentiometer that monitors the throttle plate angle and sends a voltage signal to the engine control module (ECM). When the ECM detects an abnormal voltage reading (typically outside 0.5-4.5V range) or a signal that doesn't match expected values based on engine load and speed, it sets this code. This can cause drivability issues such as poor acceleration, stalling, or reduced power.
1. Most Common Causes
- Faulty or worn throttle position sensor (TPS)
- Open, short-to-ground, or short-to-voltage wiring in the TPS circuit
- Corroded, loose, or damaged TPS connector
- Incorrect 5V reference voltage or poor ground at the sensor
- Internal potentiometer failure within the TPS
- Mechanical misalignment of the TPS on the throttle body
- Intermittent fault due to harness vibration or movement
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor acceleration or hesitation
- Engine stalling or rough idle
- Reduced power or limp mode
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect TPS wiring and connector for damage or corrosion.
Step 3: Test TPS voltage signal with a multimeter (should vary smoothly from ~0.5V at closed throttle to ~4.5V at wide open throttle).
Step 4: Check for 5V reference and ground at the TPS connector.
Step 5: If sensor is faulty, replace TPS and clear codes.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the vehicle may enter limp mode, reducing power and potentially causing unsafe driving conditions. Immediate diagnosis is advised.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the vehicle and shop rates. DIY replacement can be cheaper.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.