DTC 24

Flowchart Code 24:

Vehicle Speed Sensor (VSS) Circuit:

CIRCUIT DESCRIPTION
The Electronic Control Module (ECM) applies and monitors 12 volts on Circuit (CKT) 437. CKT 437 connects to the vehicle speed sensor, which alternately grounds CKT 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile, and the ECM will calculate vehicle speed based on the time between "pulses."
"Scan" reading should closely match with speedometer reading with drive wheels turning.

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

1. Code 24 will set, if vehicle speed equals 0 mph when:

^ Engine speed is between 1400 and 3600 rpm

^ Throttle Position Sensor (TPS) is less than 2%

^ Low load condition (low air flow)

^ 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.

2. 8 to 12 volts at the I/P connector indicates CKT 437 is open between the I/P connector and the Vehicle speed Sensor (VSS), or there is a faulty vehicle speed sensor. A voltage of less than 1 volt, at the I/P connector, indicates that CKT 437 wire is shorted to ground.

If after disconnecting CKT 437 at the vehicle speed sensor the voltage reads above 10 volts, the vehicle speed sensor is faulty. If voltage remains less than 8 volts, then CKT 437 wire is grounded. If 437 is not grounded, there is a faulty connection at the ECM or a faulty ECM.


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 (125C) or overdrive (440- T4). Refer to C-Charts Component Testing / Chart C-1A for P/N switch diagnosis check. Chart C-1A Park/Neutral Switch Diagnosis