P0122

Throttle Position Sensor/Switch A Circuit Low Input

Powertrain Speed/Idle Control Throttle Position Sensor 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Your throttle position sensor is sending a voltage signal that's too low, like a dimmer switch stuck in the off position. The engine computer can't properly gauge how much the driver is pressing the gas pedal.

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Symptoms You May Notice

3 known symptoms for this code
Engine hesitation or lack of power during acceleration
Check Engine Light illuminated
Rough idle or stalling
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors the throttle position sensor's analog voltage output, which normally ranges from 0.5V (closed throttle) to 4.5V (wide open throttle). When the signal drops below the expected minimum threshold at idle, the ECU logs a fault and cannot accurately calculate fuel injection and ignition timing.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
TPS Voltage at Idle 0.5V – 1.0V Below 0.5V
TPS Voltage WOT 4.0V – 4.8V Below 3.5V under load
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Throttle Position Sensor Connector
Inspect and clean the TPS connector pins for corrosion or loose contacts; reseat firmly.
2
Engine Wiring Harness
Check the TPS circuit wiring for breaks, pinches, or corrosion between the sensor and ECU.
3
Throttle Position Sensor
Replace the TPS unit if connector and wiring are intact and voltage remains low.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0122 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code P0122

What happens after you fix the fault

Once the fault is repaired, P0122 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.