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Home / DTC / P0123 — Throttle Position (TP) Sensor Circuit High Voltage

P0123 — Throttle Position (TP) Sensor Circuit High Voltage

Detailed page for trouble code P0123.

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Code

P0123

HUMMER P — Powertrain

Throttle Position (TP) Sensor Circuit High Voltage

Brand: HUMMER
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Damaged or shorted wiring harness (signal shorted to battery/5V reference)
  • Corroded, loose or contaminated TPS connector or terminals
  • Failed throttle position sensor (internal short or stuck potentiometer)
  • Poor or open sensor ground or reference circuit
  • PCM/ECM internal fault (rare)
  • Aftermarket parts or recent repairs with incorrect wiring

Symptoms

  • Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
  • Poor idle quality or unstable idle
  • Reduced engine power or activation of limp/derate mode
  • Throttle hesitation, surging, or poor throttle response
  • Inconsistent throttle readings on scan tool live data

What to check

  • Retrieve freeze frame and live data with OBD-II scanner; confirm TP sensor voltage and related parameters
  • Visual inspection of throttle body, TPS connector and wiring for damage, corrosion, pin push-out, or aftermarket splices
  • Back-probe TPS connector with key ON (engine OFF) and measure: reference voltage, signal voltage, and ground continuity
  • Wiggle test wiring while watching live TPS voltage for intermittent changes
  • Check for related codes (e.g., reference or ground circuit codes)
  • Compare TPS voltage to expected values at closed and wide open throttle

Signal parameters

  • Reference (Vref): approximately 5.0 V (check OEM spec)
  • Signal at closed throttle: ~0.4–1.0 V (sensor dependent)
  • Signal at wide-open throttle: ~4.0–4.5 V (sensor dependent)
  • Signal behavior: smooth, monotonic change with throttle motion; no spikes or dropouts
  • Ground: near 0 V; continuity to chassis ground should be low (

Diagnostic algorithm

  1. Read DTCs, note freeze frame and related codes. Clear codes and perform a test drive to verify repeat. 2) Perform a visual inspection of the TPS connector, pins and wiring harness for damage, corrosion, pin push-out or aftermarket splices. Repair any obvious issues. 3) With ignition ON (engine OFF) back-probe the TPS connector: measure reference (should be ~5 V), measure signal voltage at closed throttle (should be in expected closed range), and verify ground continuity. 4) If signal voltage is higher than expected with ignition ON and throttle closed, disconnect the TPS connector and re-measure the harness signal pin voltage. If the high voltage remains with sensor disconnected, suspect short to battery/ignition or PCM fault. If voltage returns to normal with connector disconnected, suspect TPS internal failure. 5) Wiggle the harness and connectors while monitoring live TPS voltage to find intermittent shorts. 6) Use an oscilloscope if available to check signal for noise/spikes while operating throttle. 7) If wiring is faulty, repair: replace damaged wiring, correct shorts to 12 V or to Vref, clean/replace connector. If wiring checks good and sensor shows abnormal readings, replace TPS/throttle body assembly per OEM procedure. 8) After repair, clear codes, perform functional tests and road test to confirm fault does not return. Document any repairs.
  2. Note: follow safety procedures when probing connectors; avoid shorting terminals to chassis or battery.

Likely causes

  • TPS signal wire shorted to fused 12V/ignition feed or 5V reference
  • Open or high-resistance ground causing elevated sensor output reading
  • Internal TPS failure producing abnormally high voltage
  • Connector corrosion or pin pushed out causing intermittent high reading

Fault status

⚠️ Status
P0123 — Throttle Position (TP) Sensor Circuit High Voltage: PCM detected TP sensor output voltage above expected range (over-voltage).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

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