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Home >> GMC >> 1987 >> Forward Control 6.2 J, Automatic, 475/M40 >> Repair and Diagnosis >> Engine Performance >> System >> CCC TBI Tests W/Codes >> Diagnostic Charts >> Code 24 - Vehicle Speed Sensor Fault ("Scan" Diagnostics) >> Test Description

Test Description

NOTE: Test numbers refer to test numbers on diagnostic chart.

Code 24 will set if the following conditions exist for at least 3 seconds:

The above conditions are met during a road load deceleration.

  1. This monitors ECM voltage on circuit No. 437. With wheels turning, pulsing action will result in varying voltage. Variation will be greater at low wheel speeds to an average of 4-6 volts at about 20 MPH.
  2. A voltage of less than one volt at ECM connector indicates that circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS. If voltage now reads above 10 volts, VSS is faulty. If voltage remains less than 10 volts, circuit No. 437 wire is grounded. If circuit No. 437 is not grounded, check for faulty ECM connector or ECM.
  3. A steady 8-12 volts at ECM connector indicates circuit No. 437 is open or faulty VSS.
  4. This is a normal voltage that indicates a possible intermittent condition.