P0122
UniversalThrottle/Pedal Position Sensor/Switch A Circuit Low Input
Medium SeverityThis code indicates that the engine computer (ECM) is receiving an abnormally low voltage signal from the primary Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APP). This signal is crucial for determining how much throttle is being applied, and a low input can lead to erratic engine behavior, reduced power, or the vehicle entering 'limp mode' to prevent damage.
⚠️ Before You Begin (Safety First)
Always ensure the vehicle is turned off and the key removed before inspecting electrical components. For electrical testing, use proper diagnostic tools and follow the vehicle's service manual. Disconnect the battery's negative terminal before performing any significant electrical work to prevent accidental shorts or damage.
Common Symptoms
- Check Engine Light illuminated
- Reduced engine power or 'limp mode'
- Rough or erratic idle
- Hesitation or stalling during acceleration
- Difficulty starting the engine
- Vehicle may not accelerate above a certain speed
Common Causes
- Faulty Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APP)
- Open or short circuit in the sensor's wiring harness
- Poor electrical connection at the sensor or ECM
- Corrosion in the sensor connector
- Faulty Engine Control Module (ECM) (rare)
Frequently reported on: Honda Civic (2001-2005), Toyota Camry (1997-2001), Ford F-150 (1997-2003), Chevrolet Silverado (1999-2007), Nissan Altima (2002-2006)
Diagnostic Steps
- Visually inspect the Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APP) wiring harness and connectors for damage, corrosion, or loose connections.
- Check for proper voltage supply (usually 5V) and ground at the sensor connector using a multimeter, following your vehicle's wiring diagram.
- Test the sensor's signal voltage output across its operational range (e.g., from closed to wide-open throttle) using a multimeter or a scan tool with live data. Look for smooth, consistent voltage changes.
- If wiring and connections are good and the sensor output is consistently low or erratic, replace the Throttle Position Sensor (TPS) or Accelerator Pedal Position Sensor (APP).
- After replacement, clear the fault code with an OBD-II scanner and test drive the vehicle to confirm the repair.
👨🔧 When to Call a Professional
If you've checked wiring and connections and the sensor itself tests good, or if you lack specialized diagnostic tools like a multimeter or scan tool with live data, it's time to consult a professional mechanic. An accurate diagnosis of wiring harnesses or the ECM often requires advanced equipment and expertise.
Commonly Asked Questions
Can I drive with a P0122 code?
It is not recommended. The vehicle may have reduced power or go into limp mode, making it unsafe to drive, especially in traffic. Address the issue promptly.
Is P0122 always a bad sensor?
Not always. While a faulty sensor is common, the issue could also be in the wiring harness (shorts, opens), poor electrical connections, or rarely, a problem with the Engine Control Module (ECM).
How do I test the Throttle Position Sensor (TPS)?
You can test a TPS with a multimeter. With the ignition on (engine off), backprobe the signal wire and ground, then slowly open the throttle. The voltage should smoothly increase from a low voltage (e.g., 0.5V) to a higher voltage (e.g., 4.5V) without drops or spikes.
What is 'limp mode'?
Limp mode is a protective feature where the vehicle's computer limits engine power and speed to prevent further damage when a serious fault is detected, such as an incorrect throttle signal.
Do I need to calibrate a new TPS?
Some vehicles may require a TPS relearn procedure after replacement, which can often be done with a professional scan tool or by following specific manufacturer instructions. Consult your service manual.