With TBI

Fig. 186 - Code 24 Vehicle Speed Senor (VSS):

Fig. 187 - Code 24 Vehicle Speed Sensor (VSS):

CODE 24

VEHICLE SPEED SENSOR (VSS)

CIRCUIT FAULT

VIN R (2.5L) VIN U (2.5L)

FUEL INJECTION (TBI)


Circuit Description: Vehicle speed information is supplied to the ECM by the vehicle speed sensor, which is a permanent magnet (PM) generator mounted in the transmission. The PM generator produces a pulsing voltage when vehicle speed exceeds 3 MPH. The A/C voltage level and number of pulses increase with vehicle speed. The ECM converts the pulsing voltage to MPH and the MPH can be displayed with a "scan" tool.
The function of VSS buffer used previously is incorporated into the ECM. The ECM supplies the signal for the instrument panel (4000 pulses per mile) for operating the speedometer and odometer.

Test Description: Numbers below refer to circled numbers on Diagnostic Charts.

1. Code 24 will set if vehicle speed equals 0 mph when:
Engine speed is between 1100 and 3600 rpm.
TPS is less than 2%
Low load condition, low MAP voltage, high manifold vacuum.
Not in Park or Neutral.
All conditions met for 5 seconds.
These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning.
The PM generator produces a signal only if the wheels are turning above 3 mph.

Diagnostic Aids:

"Scan" should indicate a vehicle speed whenever the drive wheels are turning greater than 3 mph.
A faulty or misadjusted Park/neutral switch can result in a false Code 24. Use a "Scan" and check for proper signal, while in drive. Refer to CHART C-1A P/N switch check.
If Code 24 is intermittent, refer to DIAGNOSIS BY SYMPTOM.
Check circuit 400 and 401 for proper connections, that they are clean and tight and the harness is routed correctly.
A problem in circuit 993 will not affect the VSS input or the "scan" readings.