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 MANUALSCHEVROLET1998EXPRESS 1 TON VAN V8-5.7L VIN RREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTHROTTLE POSITION SENSORTESTING AND INSPECTIONTHROTTLE POSITION SENSOR (DTCS SET)
1998 Chevrolet Express 1 Ton Van V8-5.7L VIN R
Throttle Position Sensor (DTCs Set)
1998 Chevrolet Express 1 Ton Van V8-5.7L VIN RSECTION Throttle Position Sensor (DTCs Set)
The VCM 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 VCM detects the throttle is moving.
When the VCM detects a malfunction with the TP sensor circuits, 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.
A problem in the TP Sensor 5V reference or signal circuits should set either a DTC P0122 or DTC P0123. A problem with the TP Sensor ground circuit may set DTCs P0123 and P0117. Once a DTC is set, the VCM will use an artificial default value based on mass air flow for TP Sensor and some vehicle performance will return. A high idle may result when either DTC P0122 or DTC P0123 is set.
When the VCM detects a malfunction with the TP sensor circuits, 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.
A problem in the TP Sensor 5V reference or signal circuits should set either a DTC P0122 or DTC P0123. A problem with the TP Sensor ground circuit may set DTCs P0123 and P0117. Once a DTC is set, the VCM will use an artificial default value based on mass air flow for TP Sensor and some vehicle performance will return. A high idle may result when either DTC P0122 or DTC P0123 is set.
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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.