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Home >> Buick >> 1996 >> Roadmaster Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0121 - TP Sensor Circuit Insufficient Activity >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform Powertrain On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, select ENGINE 1 DATA LIST and monitor TP sensor voltage while moving throttle from closed position to wide open position. Scan tool should display TP sensor voltage at less than one volt to greater than 4 volts, as throttle position is changed. If voltage reading is not as specified, go to next step. If voltage reading is as specified, go to step 4).
  3. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within the conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function, then enter DTC P0121. If scan tool indicates this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see DIAGNOSTIC AIDS.
  4. Disconnect TP sensor harness connector. Observe TP sensor display on scan tool. If about zero volts is displayed, go to next step. If not, go to step 7).
  5. Using a fused jumper wire, jumper TP sensor 5-volt reference circuit to TP sensor signal circuit. If TP sensor is about 5 volts, go to next step. If TP sensor value is not as specified, go to step 8).
  6. Replace TP sensor. After replacing TP sensor, go to step 10).
  7. Check TP signal circuit for short to voltage. Check TP sensor ground circuit for high resistance between PCM and TP sensor. Check TP sensor ground circuit for poor connection. Repair as necessary. After repairs, go to step 10). If circuits are okay, go to step 9).
  8. Check TP sensor signal circuit or 5-volt reference circuit for poor connection. Check signal circuit or 5-volt reference circuit for high resistance between PCM and TP sensor. Replace as necessary. After repairs, go to step 10). If circuits are okay, go to next step.
  9. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  10. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0121. Operate vehicle within the conditions that set the DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
  11. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.
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