LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 208 (Automatic Transmission - ALLISON - Diagnosis) >> Diagnostic Tests >> DTC P0721: Output Speed Sensor Circuit - Performance >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the diagnostic system check? If so, go to next step. If not, see DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Install the scan tool. Turn ignition on, engine off. Record the DTC failure records. Start the engine. Using the scan tool, check ignition voltage. Is the voltage 9-18 volts? If so, go to next step. If not, see DTC P0562: SYSTEM VOLTAGE LOW  or DTC P0563: SYSTEM VOLTAGE HIGH  .
  3. Turn ignition off. Disconnect the C2 connector at the TCM. Measure the resistance of output speed sensor circuit between TCM connector C2 terminals No. 15 and 16. See COMPONENT RESISTANCE  under ELECTRONIC COMPONENT SPECIFICATIONS. Is the speed sensor resistance within the specified values? If so, see DIAGNOSTIC AIDS . If not, go to next step.
  4. Disconnect the wiring harness from the output speed sensor. Measure the resistance between the speed sensor terminals. See COMPONENT RESISTANCE  under ELECTRONIC COMPONENT SPECIFICATIONS. Is the speed sensor resistance within the specified values? If so, go to next step. If not, go to step  6.
  5. Repair the vehicle wiring harness. Is the repair complete? If so, go to step  7.
  6. Replace the output speed sensor. See SPEED SENSORS  under REMOVAL & INSTALLATION. Is the repair complete? If so, go to next step.
    CAUTION: Do not rotate the speed sensor in the retaining bracket. Orientation is fixed, and if changed, may cause improper operation.
  7. Perform the following procedure to verify the repair:
    • Clear the DTC.
    • Drive the vehicle under normal operating conditions.
    • Using the scan tool, monitor output speed sensor operation.

    Did the DTC return? If so, go to step  1. If not, system is okay.

scientia non olet · About LEMON Manuals