P0123

Throttle Position Sensor/Switch A Circuit High Input

Powertrain Fuel and Air Metering Throttle Control 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

The throttle position sensor is sending a signal that's too high, like a volume knob stuck at maximum. The engine computer thinks the throttle is wide open when it actually isn't.

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Symptoms You May Notice

3 known symptoms for this code
Check Engine Light illuminated
Engine hesitation or surging at idle
Poor fuel economy
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors voltage from the Throttle Position Sensor (TPS) to determine throttle opening angle. The sensor typically outputs 0.5–4.5V as the throttle moves from closed to open. A high input means the voltage exceeds the maximum expected threshold, indicating either a sensor malfunction or wiring issue.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
TPS Voltage 0.5V–4.5V (closed to wide open) >4.5V or exceeds max calibrated voltage
Throttle Angle 0–100% >100% or implausible high reading
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
TPS connector and wiring
Inspect the connector for corrosion, loose pins, or damaged insulation; reseat or clean contacts.
2
Throttle Position Sensor
Remove and replace the TPS unit if voltage remains high after cleaning connectors.
3
Throttle body and linkage
Check for mechanical binding or debris preventing normal throttle return and operation.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0123 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 P0123

What happens after you fix the fault

Once the fault is repaired, P0123 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.