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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 141 (Engine Controls Self-Diagnostics - 5.7L - Bi-Fuel) >> Diagnostic Tests >> DTC P0121: TP Sensor Angle Out Of Range >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Turn ignition on. Using scan tool, communicate with AF ECM. Observe TP sensor angle. Observe the TP sensor angle data parameter. Does the scan tool display the throttle angle less than 2 percent? If yes, go to step  3 . If no, go to step  6 .
  3. Depress the throttle slowly to Wide Open Throttle (WOT). Does the scan tool display the throttle angle greater than 98 percent? If yes, next step. If no, go to step  6 .
  4. Release throttle. Does the scan tool display the throttle angle less than 2 percent? If yes, go to next step. If no, go to step  6 .
  5. Fault is not present at this time. Are any additional DTCs are set and need to be repaired? If yes, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  6. Disconnect the TP sensor harness connector. Other DTCs may set. Connect a fused jumper between the TP signal circuit terminal and the 5-volt reference circuit terminal. Observe the TP sensor voltage data parameter. Does the scan tool display the TP sensor voltage greater than 4.9 volts? If yes, go to next step. If no, go to step  10 .
  7. Remove jumper wire. Connect the Digital Multimeter (DMM) test leads between the TP sensor 5-volt reference circuit terminal and a known-good ground. Measure the voltage on the 5-volt reference circuit. Is the voltage within 4.8-5.2 volts? If yes, go to next step. If no, go to step  12 .
  8. Using a fused jumper wire, connect the TP sensor signal circuit terminal to a known-good ENGINE ground. If the jumper fuse opens, repair the signal circuit shorted to battery voltage. Other DTCs may set. Observe the TP sensor voltage data parameter. Does the scan tool display TP sensor voltage less than 0.08 volt? If yes, go to next step. If no, go to step  14 .
  9. Connect a fused jumper between the TP signal circuit terminal and the 5-volt reference circuit terminal. Connect another fused jumper between the TP sensor ground circuit terminal and the 5-volt reference circuit jumper. Other DTCs may set. Observe the TP sensor voltage data parameter. Does the scan tool display TP sensor voltage less than 0.08 volt? If yes, go to step  11 . If no, go to step  15 .
  10. Test the TP signal circuit for a short to ground or to the sensor ground circuit. Repair wiring as necessary. Was a wiring repair made? If yes, go to step  19 . If no, go to step  18 .
  11. Test the TP signal circuit for a short to voltage (jumper fuse opens or a short to the 5-volt reference circuit). Repair wiring as necessary. Was a wiring repair made? If yes, go to step  19 . If no, go to step  16 .
  12. Turn ignition off. Disconnect both AF ECM connectors. Turn ignition on, with engine off. Re-measure the voltage on the 5-volt reference circuit. Is the voltage within 4.8-5.2 volts? If yes, go to step  18 . If no, go to next step.
  13. Test the 5-volt reference circuit for a short to voltage (greater than 5.2 volts), or a short to ground or high circuit resistance (less than 4.8 volts). Repair wiring as necessary. Was a wiring repair made? If yes, go to step  19 . If no, go to step  17 .
  14. Inspect the TP sensor Signal circuit for an open or high resistance condition between the AF ECM connector terminal and the circuit splice. Inspect the AF ECM connector and any in-line connectors, if applicable, for proper terminal contact. Repair wiring or terminals as necessary. Was a repair necessary? If yes, go to step  19 . If no, go to step  18 .
  15. Test the TP sensor ground circuit for high resistance or poor terminal contact at the PCM connector. Repair wiring or terminal contact as necessary. Was a repair made? If yes, go to step  19 . If no, go to step  17 .
  16. Replace TP sensor. See THROTTLE POSITION SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE. When complete, go to step  19 .
  17. Replace PCM. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE. Program (flash) PCM with correct vehicle software and calibration. See POWERTRAIN CONTROL MODULE REPROGRAMMING  under PROGRAMMING. To perform CKP variation learn procedure, a switchover to gasoline operation is necessary. Remove CNG fuse (20-amp) located in underhood fuse block to perform switchover. Perform CKP system variation learn procedure. See CRANKSHAFT POSITION SENSOR SYSTEM VARIATION LEARN PROCEDURE  under PROGRAMMING. After performing repairs and procedures, go to step  19 .
  18. Replace AF ECM. See ALTERNATE FUEL ENGINE CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. Program (flash) AF ECM with correct vehicle software and calibration. See ALTERNATE FUEL ENGINE CONTROL MODULE  under PROGRAMMING. After performing repairs and procedures, go to next step.
  19. Using scan tool, clear the DTC information from BOTH control modules. Operate the vehicle under the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC  . Using scan tool parameter DTC STATUS, ensure that this DTC runs. Did this DTC RUN and PASS? If yes, system is okay. If no, go to step  2 .
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