Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code P0123, Throttle Position Sensor Signal High "S" & "T" Series 4.3L (VIN W): Notes
Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from about .5 volt or at idle to about 4 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by control module for fuel control and for most other control module control outputs. On non-adjustable TPS sensors, each time voltage drops below 1.25 volts and stops, control module assumes this value as 0 throttle angle and measures percent throttle from this point on. With Code P0123 set, throttle position will default to 19 percent and Tech 1 will not indicate fault value. Control module will illuminate Malfunction Indicator Light (MIL).
- If TP signal is greater than 4.8 volts, fault is present.
- With TP sensor disconnected, TP sensor voltage should decrease. This test verifies that control module and wiring are okay.
- Probing ground circuit with a test light checks sensor ground circuit. This isolates a faulty sensor, control module or open ground circuit.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.