DTC 24

Code 24 Chart:

Wiring Diagram For VSS:

CIRCUIT DESCRIPTION:

Vehicle speed information is provided to the ECM by the Vehicle Speed Sensor (VSS). It is a Permanent Magnet (PM) generator and is mounted in the transmission. The generator produces a pulsing voltage whenever the vehicle speed is over 3 mph. The voltage level and number of pulses increase as the vehicle's speed increases. The ECM converts the pulse voltage into miles per hour. This data is used for calculations and can be displayed on the "Scan" tool.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. A Code 24 will set if vehicle speed is one mph or less when:
a. Transmission is not in park or neutral.
b. Engine speed is between 1125 and 4400 RPM.
c. MAP is less than 30 kPa.
d. Low load condition (low air flow).
e. All conditions must be met for 5 seconds. These conditions are met during a road load deceleration.
f. The PM generator only produces a signal if the drive wheels are turning greater than 3 mph.


DIAGNOSTIC AIDS:

1. The "Scan" tool should indicate a vehicle speed whenever the drive wheels are turning greater than 3 mph.
2. A problem in circuit 434 will not affect the VSS input or the readings on the "Scan" tool.
3. On automatic transmissions, a faulty or mis-adjusted park/neutral switch can result in a false Code 24. Use a "Scan" tool and check for a proper signal while in drive or overdrive. See CHART C-1A for P/N switch diagnosis.
4. Carefully check circuits 400 and 401 for proper connections to be sure they are clean and tight. Check for proper harness routing. If a Code 24 is intermittent, see DIAGNOSIS BY SYMPTOM.