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Home >> Chevrolet >> 2001 >> Camaro Base, 2D Convertible, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 43 (Engine Control System Self-Diagnostics - 3.8L) >> Diagnostic Tests >> DTC P1221: Throttle Position Sensor 1 & 2 Disagree >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
  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. NOTE: If DTCs P1120, P1220 or P1518 are also set, refer to those DTCs first for further diagnosis. See DTC P1120: THROTTLE POSITION SENSOR 1 CIRCUIT , DTC P1220: THROTTLE POSITION SENSOR OUT OF RANGE  or DTC P1518: LOSS OF COMMUNICATION BETWEEN PCM & THROTTLE ACTUATOR CONTROL MODULE  .
  2. Turn ON the ignition, with the engine OFF. With a scan tool, observe the Agree/Disagree parameter of the TP sensors. Does the scan tool indicate Agree? If yes, go to next step. If no, go to step  4.
  3. With a scan tool, observe DTC Info. Move the harness and related connectors while observing the DTC information. Does the harness movement cause this DTC to fail this ignition cycle? If yes, go to step  10. If no, see DIAGNOSTIC AIDS .
  4. Turn OFF the ignition. Disconnect the TAC. Turn ON the ignition, with the engine OFF. Measure the voltage on both the TP 1 and the TP 2 5-volt reference circuits using a DMM that is connected to a good ground. Does the voltage measure within 3.9-4.6 V? If yes, go to next step. If no, go to step  11.
  5. Measure the voltage on both the TP 1 and the TP 2 signal circuits using a DMM that is connected to a good ground. Does the voltage measure within 3.9-4.6 V? If yes, go to next step. If no, go to step  12.
  6. Turn OFF the ignition. Measure for continuity between the TP 1 5-volt reference and the TP 2 5-volt reference at the TAC using a DMM. Does the DMM indicate continuity? If yes, go to step  13. If no, go to next step.
  7. Measure for continuity between the TP 1 signal and the TP 2 signal at the TAC using a DMM. Does the DMM indicate continuity? If yes, go to step  13. If no, go to next step.
  8. Disconnect the TAC module. Leave the TAC disconnected. Measure for continuity between the TP 1 5-volt reference and the TP 2 5-volt reference at the TAC module harness connector using a DMM. Does the DMM indicate continuity? If yes, go to step  15. If no, go to next step.
  9. Measure for continuity between the TP 1 signal and the TP 2 signal at the TAC module harness connector using a DMM. Does the DMM indicate continuity? If yes, go to step  16. If no, go to step  14.
  10. Repair the harness and connections as necessary. After repairs, go to step  17.
  11. Check for short to voltage in the 5-volt reference circuit. Did you find and correct the condition? If yes, go to step  17. If no, go to step  14.
  12. Check for short to voltage in the signal circuit. Did you find and correct the condition? If yes, go to step  17. If no, go to step  14.
  13. Replace the throttle body of the TAC assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  17.
  14. Replace the TAC module. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  17.
  15. Repair the TP 1 and the TP 2 5-volt reference circuits that are shorted together. After repairs, go to step  17.
  16. Repair the TP 1 and TP 2 signal circuits that are shorted together. After repairs, go to step  17.
  17. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  18. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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