Code
P0123
ISUZU
P — Powertrain
Throttle Position Sensor Circuit High
Views:
UK: 22
EN: 48
RU: 20
AI status
Completed
Completed
100%
Causes
- Damaged or shorted TPS signal wire to 5V or other voltage source
- Faulty throttle position sensor (open/plastic gear wear or internal short)
- Poor TPS connector contact, corrosion, bent pins or water ingress
- Faulty or contaminated throttle body assembly affecting sensor travel
- ECM/PCM input circuit fault or internal short
- Aftermarket wiring or recent repairs disturbing the harness
Symptoms
- Check Engine Light (MIL) on
- Reduced engine performance or limp mode in some vehicles
- High or erratic idle, hesitation, or surging
- Poor throttle response or unexpected acceleration behavior
- Diagnostic trouble code P0123 stored in ECM
What to check
- Retrieve freeze frame and live data with a scan tool: monitor TPS voltage/PID at closed throttle and during accelerator travel
- Perform visual inspection of TPS connector, wiring harness and throttle body for damage, corrosion or contamination
- Check for related codes (e.g., TPS low, pedal position sensor, throttle actuator codes)
- Backprobe TPS connector and confirm reference (usually 5V), signal voltage and ground at closed throttle and during travel
- Inspect ECM connector and wiring continuity if wiring looks intact
- Wiggle test harness and replay live data to see if voltage changes with movement
Signal parameters
- Typical TPS signal: ~0.2–1.0 V at closed throttle (idle) and ~4.0–4.8 V at wide-open throttle (vehicle-dependent)
- TPS reference/return: 5.0 V reference supply and dedicated ground (check for stable 5.0 V and low-resistance ground)
- Signal should change smoothly and proportionally with throttle movement (no jumps, spikes or drops)
Diagnostic algorithm
- Use a scan tool to verify P0123 and view live TPS voltage at closed throttle and while slowly opening throttle. Note values and behavior.
- Visually inspect TPS connector and wiring for corrosion, bent pins, damage, or water intrusion. Repair any obvious faults.
- With ignition ON (engine off), backprobe the TPS: verify reference voltage (~5 V), signal voltage (should be ~0.2–1.0 V at closed), and ground continuity to chassis/ECM.
- If reference or ground is out of range, trace and repair 5V supply or ground circuit back to ECM before replacing the sensor.
- If voltages at TPS harness are correct but signal is high or erratic when moving the throttle, disconnect TPS and measure sensor output directly at the sensor connector while slowly moving throttle. Replace TPS if output remains out of range.
- If TPS output is normal at the sensor but high at the ECM, check wiring continuity and for shorts between signal and 5V or other voltage sources. Repair or replace harness as needed.
- After repairs, clear codes and perform road test while monitoring TPS voltage to confirm correct operation and no recurrence of P0123.
- If wiring and sensor check good and issue persists, test ECM input circuit or consult manufacturer service information for ECM replacement procedure.
Likely causes
- Short from TPS signal wire to ignition-switched 5V reference or to another high-voltage source
- TPS failed internally (output stuck high or potentiometer worn/spiking)
- Corroded/loose connector at TPS or ECM causing high reading
- Damaged harness insulation with intermittent contact causing high voltage reading
Fault status
Status
P0123 — Throttle Position Sensor Circuit High: ECM detected TPS signal voltage above the expected range. This indicates a high-voltage condition on the TPS signal circuit caused by sensor failure, wiring/connector fault, or ECM input problem. Address wiring and sensor before considering ECM replacement.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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