P0520
Closed Throttle Position Switch Malfunction
Powertrain Speed/Idle Control Throttle Position Sensing 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your engine's throttle position sensor isn't sending the right signal when the throttle is fully closed, like a light switch that won't click into the off position. The ECU can't confirm the engine is at idle, which affects fuel delivery and engine control.

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Symptoms You May Notice
3 known symptoms for this code
Engine stalling or rough idle at stops
Poor fuel economy and hesitation during acceleration
Check Engine Light illumination
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the Closed Throttle Position (CTP) switch signal, which should be active (high voltage) when the throttle butterfly is fully closed. The ECM expects a clean transition from active to inactive as the throttle opens and back to active when fully closed. If this signal is missing, intermittent, or inverted, the ECU cannot confirm proper idle state.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
CTP Switch Signal at Idle Active/High (4.5-5V) when throttle fully closed Inactive/Low (<0.5V) or no signal change
Signal Continuity Continuous clean signal without dropout Intermittent signal or constant dropout
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Throttle Position Sensor connector
Disconnect and reseat the TPS connector at the throttle body to eliminate corrosion-related signal loss.
2
Throttle body and intake valves
Clean carbon deposits from the throttle butterfly and valve seat using carburetor cleaner to ensure full closure and proper switch contact.
3
Throttle Position Sensor (TPS)
Replace the TPS unit if signal remains faulty after cleaning and connector inspection.