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Home >> Oldsmobile >> 1987 >> Calais Base, 4D Sedan, 2.3 D >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> 2.3L VIN [D] CEC Tests W/Codes >> Diagnostic Code Flow Charts (Code Charts) >> Code 24 - VSS Circuit >> Notes

Code 24 - VSS Circuit: Notes

The speed sensor, a Permanent Magnet (PM) generator, provides ECM with vehicle speed information. The PM generator, mounted in the transmission, produces a pulsing voltage signal whenever vehicle speed is greater than 3 MPH. The AC voltage level and the number of pulses increase with vehicle speed. ECM converts pulsing voltage to MPH, which is used for calculations. MPH can be displayed with a scan tool. Output of generator can be monitored with a digital voltmeter on the AC scale while rotating generator.

The function of the VSS buffer used in past models years has been incorporated into the ECM. The ECM supplies the signal for the instrument panel (4000 pulses per mile) to operate the speedometer, and for the odometer and cruise control (2000 pulses per mile).

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. Code 24 will set only when following conditions are met:
    • Engine RPM is between 1600 and 3600.
    • TPS is less than 7 percent.
    • Gear selector not in park or neutral.
    • All conditions met for 20 seconds.
    • No Codes 21 or 22.

    The above conditions are met during road load deceleration. Ignore a Code 24 that is set when the drive wheels are turning faster than 3 MPH.

  2. Ensure that correct PROM is used before replacing ECM.
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