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 MANUALSGMC1991C3500 HD 6.2 J, STANDARD, NV4500/MT8REPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSCOMPUTERIZED ENGINE CONTROLSENGINE SENSORS & SWITCHESTHROTTLE POSITION SENSOR (TPS)

1991 GMC C3500 HD 6.2 J, Standard, NV4500/MT8

Throttle Position Sensor (TPS)

1991 GMC C3500 HD 6.2 J, Standard, NV4500/MT8SECTION Throttle Position Sensor (TPS)

Install jumper wires to enable connection of a DVOM in parallel between TPS harness connectors. Connect DVOM positive lead to Dark Blue wire terminal. Connect negative lead to Black wire terminal. See Fig 1.
Turn ignition on, engine off. Signal voltage should gradually change from less than one volt at closed throttle to about 5.0 volts at wide open throttle position. If reading is not as specified, adjust or replace TPS. See ADJUSTMENTS article in this section.
A malfunction in the TPS circuit should set a related trouble code. For further information, see appropriate article below:
- TESTS W/CODES - DIESEL
- TESTS W/CODES - GASOLINE
- TESTS W/CODES - TRANSMISSION (If Transmission Codes Are Displayed)

Also refer to TPS adjustment procedure in ADJUSTMENTS article in this section.

Fig 1: Typical Throttle Position Sensor Circuit

Courtesy of GENERAL MOTORS CORP.

RENDER: 1.0x

NO RELATED

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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.