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 MANUALSCHEVROLET1998SUBURBAN K2500, 7.4 J, PART TIMEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 2 (ENGINE CONTROLS - TESTS W/CODES - 5.7L)DIAGNOSTIC TROUBLE CODESDTC P0121 - TP SENSOR PERFORMANCEDIAGNOSTIC PROCEDURES
1998 Chevrolet Suburban K2500, 7.4 J, Part Time
Diagnostic Procedures
1998 Chevrolet Suburban K2500, 7.4 J, Part TimeSECTION Diagnostic Procedures
WARNING: This page is about a different variant/trim than selected.
- Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.
- Install scan tool. Turn ignition on, with engine off. Using scan tool, observe TP sensor value. If TP sensor value is greater than 2 percent, go to step 4). If TP sensor value is not greater than 2 percent, go to next step.
- Depress throttle while observing scan tool. Throttle value should increase from about zero percent to 99.6 percent. Release throttle. Throttle value should drop to about 2 percent. If TP sensor value is greater than 2 percent, go to next step. If TP sensor value is not greater than 2 percent, go to step 5).
- Disconnect TP sensor connector. Using scan tool, monitor TP sensor. If TP sensor voltage is about zero volts, go to step 6). If TP sensor voltage is not about zero volts, go to step 9).
- DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
- Check for poor connection at TP sensor. If a problem is found, go to next step. If no problem is found, go to step 8).
- Repair as necessary. After repairs, go to step 10).
- Replace TP sensor. After replacing sensor, go to step 10).
- Replace VCM. After replacing VCM, go to next step.
- Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within the conditions for setting this DTC. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, repeat step 2).
- Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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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.