LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2003 >> Seville SLS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0121: TP Sensor Performance >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedures

  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Inspect for the following:
    • Disconnected, damaged, or incorrectly routed vacuum hoses.
    • Missing or damaged Manifold Absolute Pressure (MAP) sensor seal.
    • Restrictions in the MAP sensor vacuum source.
    • The intake manifold vacuum leaks.

    Did you find and correct the condition? If yes, go to step  25. If no, go to next step.

    3. NOTE: The vehicle used for the comparison is not limited to the same type of vehicle as is being serviced. A vehicle known to provide an accurate reading is acceptable.
  3. Do you have access to another vehicle in which the MAP sensor pressure can be observed with a scan tool? If yes, go to next step. If no, go to step  5.
  4. Turn ignition on, with engine off. Observe the MAP sensor pressure with a scan tool. Observe the MAP sensor pressure in the known good vehicle with a scan tool. Compare the values. Is the difference between the values less than 3 kPa? If yes, go to step. If no, see DTC P0106: MAP SYSTEM PERFORMANCE .
    5. NOTE: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or very low or very high temperature may cause a reading to be slightly out of range.
  5. Turn ignition on, with engine off. Observe the MAP sensor pressure with a scan tool. The MAP sensor pressure should be within the range specified for your altitude. See Figure. Does the MAP sensor indicate the correct barometric pressure? If yes, go to next step. If no, see DTC P0106: MAP SYSTEM PERFORMANCE .
  6. Observe the MAP sensor pressure with a scan tool. Start the engine. Does the MAP sensor pressure change? If yes, go to next step. If no, see DTC P0106: MAP SYSTEM PERFORMANCE .
  7. Turn ignition off. Turn ignition on, with engine off. Observe the TP SENSOR parameter with the scan tool. Is the voltage less than 0.90 volts with the throttle in the closed position? If yes, go to next step. If no, go to step  10.
  8. Observe the TP SENSOR parameter with the scan tool. Depress the accelerator pedal slowly until the throttle is in the Wide Open position. Release the accelerator pedal slowly until the throttle is returned to the Closed position. Repeat this procedure several times. Does the TP SENSOR parameter increase steadily when the pedal is depressed to more than 98 percent and then decrease steadily when the pedal is released returning to less than 1 percent? If yes, go to next step. If no, go to step  11.
    9. NOTE: The ENGINE SPEED parameter must stabilize after each commanded change.
  9. Start the engine and allow the engine to idle. Turn off all accessories. Command the Idle Air Control (IAC) valve to decrease engine speed to 500 RPM with the scan tool RPM control function. Is the engine speed within 100 RPM of the commanded RPM? If yes, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM. If no, see appropriate SYSTEM & COMPONENT TESTING article.
  10. Inspect the throttle body for a binding or damaged throttle blade and a binding or damaged throttle cable. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  11. Disconnect the TP sensor electrical connector. Observe the TP SENSOR parameter with the scan tool. Is the voltage less than 0.16 volts? If yes, go to next step. If no, go to step  16.
  12. Measure the voltage between the TP sensor 5-volt reference circuit and a good ground. Is the voltage more than 5.2 volts? If yes, go to step  17. If no, go to next step.
  13. Probe the TP sensor 5-volt reference circuit with a test light that is connected to a good ground. Is the test light off? If yes, go to step  18. If no, go to next step.
  14. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the TP sensor. Observe the TP SENSOR parameter with the scan tool. Is the voltage more than 4.9 volts? If yes, go to next step. If no, go to step  19.
  15. Turn ignition off. Remove the jumper wire. Connect a jumper wire between each of the terminals in the TP sensor harness connector and the corresponding terminal at the TP sensor. Turn ignition on, with engine off. Measure the voltage between the TP sensor low reference circuit, at the jumper wire terminal, to a good ground. Is the voltage more than 0.2 volts? If yes, go to step  20. If no, go to step  21.
    16. NOTE: Disconnecting the PCM may eliminate the short during testing.
  16. Test the TP sensor signal circuit between the PCM and the TP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step  25. If no, go to step  24.
    17. NOTE: Disconnecting the PCM may eliminate the short during testing.
  17. Test all of the branches of the 5-volt reference circuit that are shared with the TP sensor for a short to voltage. Did you find and correct the condition? If yes, go to step  25. If no, go to step  24.
  18. Test the 5-volt reference circuit between the PCM and the TP sensor for an open or for a high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  22.
  19. Test the TP sensor signal circuit between the PCM and the TP sensor for a short to ground, an open or high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  22.
  20. Test the low reference circuit between the PCM and the TP sensor for an open or for a high resistance. Did you find and correct the condition? If yes, go to step  25. If no, go to step  22.
  21. Test for an intermittent and/or poor connections at the TP sensor. Did you find and correct the condition? If yes, go to step  25. If no, go to step  23.
  22. Test for an intermittent and/or poor connections at the PCM. Did you find and correct the condition? If yes, go to step  25. If no, go to  24.
  23. Replace TP sensor. See THROTTLE POSITION SENSOR under SENSORS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to step  25.
  24. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Did you complete the replacement? If yes, go to next step.
  25. Clear the DTCs with a scan tool. Turn off the ignition for 30 seconds. Start the engine and operate vehicle within the Conditions For Running DTC. You may also operate vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to step  2. If no, go to next step.
  26. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
scientia non olet · About LEMON Manuals