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.
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HOMESERVICE MANUALSCHEVROLET1999EXPRESS 1/2 TON VAN V6-4.3L VIN WREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONTHROTTLE POSITION (TP) SENSOR
1999 Chevrolet Express 1/2 Ton Van V6-4.3L VIN W
Throttle Position (TP) Sensor
1999 Chevrolet Express 1/2 Ton Van V6-4.3L VIN WSECTION Throttle Position (TP) Sensor
Throttle Position (TP) Sensor:
The Throttle Position (TP) sensor is a potentiometer. The TP sensor is connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the VCM calculates the throttle position. As the throttle valve angle is changed (the accelerator pedal is moved), the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens, the output increases so that at Wide Open Throttle (WOT), the output voltage should be above 4.0 volts.
The VCM calculates the fuel delivery based on the throttle valve angle (driver demand). A broken or loose TP sensor may cause intermittent bursts of fuel from an injector. This may cause an unstable idle because the VCM detects the throttle is moving.
When the VCM detects a malfunction with the TP sensor circuits, one of the following DTCs will set:
^ DTC P0121 circuit performance malfunction
^ DTC P0122 circuit low
^ DTC P0123 circuit high
^ DTC P1121 intermittent circuit high
^ DTC P1122 intermittent circuit low
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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.