P0123 Throttle Position Sensor/Switch "A" Circuit High Input

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P0123 Throttle Position Sensor/Switch "A" Circuit High Input

What Does Code P0123 Mean?

Diagnostic Trouble Code P0123 indicates that the Engine Control Module (ECM/PCM) has detected an abnormally high voltage signal from the Throttle Position Sensor (TPS) "A" circuit. The voltage exceeds the expected operating range, typically due to an open circuit, short to voltage, faulty TPS, or damaged wiring.

Symptoms

  • Check Engine Light (MIL) illuminated
  • Reduced engine power (Limp Mode)
  • Poor or erratic throttle response
  • Sudden increase in idle speed
  • Engine hesitation
  • Poor acceleration
  • Transmission shift issues on some vehicles

Possible Causes

  • Faulty Throttle Position Sensor (TPS)
  • Open circuit in the TPS signal wire
  • Short to battery voltage
  • Loose or disconnected TPS connector
  • Damaged wiring harness
  • Faulty electronic throttle body
  • ECM failure (rare)

Typical Circuit

ECM (5V Reference)
        │
        ├────────────► TPS Sensor A
        │
Ground ─┘
        │
Signal ─────────────► ECM

Signal Flow

Accelerator Pedal
        │
        ▼
Throttle Body
        │
TPS Sensor A
        │
High Voltage Signal
        ▼
ECM
        │
Throttle Control
Fuel Injection
Ignition Timing

How to Diagnose

1. Visual Inspection

  • Inspect the TPS connector for loose, damaged, or corroded terminals.
  • Check the wiring harness for broken wires or contact with high-voltage circuits.
  • Inspect the throttle body for damage or binding.

2. Live Data Test (Autel)

  • Open Diagnosis → Engine → Live Data.
  • Monitor Throttle Position Sensor A.
  • With the throttle closed, the TPS reading should normally be around 10–20% (manufacturer dependent).
  • If the scan tool shows a very high value (near 100%) while the throttle is closed, suspect a high-input condition.
  • Compare TPS A with TPS B (if equipped). A significant mismatch indicates a sensor or circuit fault.

3. Multimeter Test

  • Verify the 5V reference voltage.
  • Check sensor ground continuity.
  • Measure TPS signal voltage while moving the throttle plate.
  • Inspect the signal wire for an open circuit or short to voltage.

4. Smoke Test (If Applicable)

A smoke test is generally not required for P0123 because it is primarily an electrical fault. Perform a smoke test only if additional symptoms suggest an intake vacuum leak.

Common Repairs

  • Replace the faulty TPS sensor.
  • Replace the electronic throttle body if the TPS is integrated.
  • Repair open or damaged wiring.
  • Repair or replace damaged electrical connectors.
  • Perform a throttle relearn procedure if required by the manufacturer.
  • Clear the DTC and verify proper throttle operation.

Severity

High. P0123 often causes limp mode and serious throttle control problems, significantly affecting vehicle drivability and safety.

Important Note

Throttle Position Sensor voltage ranges, connector pinouts, wiring colors, and throttle relearn procedures vary between manufacturers. Always consult the factory service information for the specific vehicle before performing diagnostics or repairs.

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