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 MANUALSPONTIAC1998FIREBIRD V8-5.7L VIN GREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTHROTTLE POSITION SENSORDESCRIPTION AND OPERATION
1998 Pontiac Firebird V8-5.7L VIN G
Throttle Position Sensor: Description and Operation
1998 Pontiac Firebird V8-5.7L VIN GSECTION Description and Operation
DESCRIPTION
The Throttle Position (TP) sensor is a potentiometer. The TP sensor is connected to the throttle shaft on the throttle body. The PCM calculates throttle position by monitoring the voltage on the signal line. The TP sensor signal changes as the throttle valve angle is changed (accelerator pedal moved).
OPERATION
The TP sensor signal voltage is low at a closed throttle position. The TP sensor signal voltage increases as the throttle valve opens so that at Wide Open Throttle (WOT), the output voltage should be above 4.0 volts.
The PCM calculates fuel delivery based on 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 PCM detects the throttle is moving.
The following DTCs set when the PCM detects a malfunction with the TP sensor circuits:
^ DTC P0121 TP Sensor Circuit Insufficient Activity.
^ DTC P0122 TP Sensor Circuit Low Voltage.
^ DTC P0123 TP Sensor Circuit High Voltage.
^ DTC P1121 TP Sensor CKT Intermittent High Voltage.
^ DTC P1122 TP Sensor CKT Intermittent Low Voltage.
RENDER: 1.0x
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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.