DTC 24

Vehicle Speed Sensor Circuit:

Circuit Description
The ECM applies and monitors 12 volts on CKT 437. CKT 437 connects to the vehicle speed buffer 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."

Tech 1 "Scan" tool reading should closely match the speedometer reading with drive wheels turning.

Disregard a Code 24 set when drive wheels are not turning.

Code 24 Diagnostic Chart:

Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Code 24 will set if vehicle speed is less than 2 mph when:
^ Engine speed is greater than 1400 rpm.
^ TPS is greater than 5%.
^ Load condition is less than 25 kPa of vacuum.
^ All conditions met and accumulated for 30 seconds.

2. 8-12 volts, at the lip connector, indicates CKT 437 is open between the lip connector and the VSS, or there is a faulty vehicle speed sensor. A voltage of less than 1 volt, at the lip connector, indicates that CKT 437 wire is shorted to ground. If, after disconnecting CKT 437 at the vehicle speed buffer, the voltage reads above 10 volts, the vehicle speed buffer is faulty. If voltage remains less than 8 volts, then CKT 437 wire is grounded. If CKT 437 is not grounded, there is a faulty connection at the ECM, or a faulty ECM.


Diagnostic Aids
Tech 1 "Scan" tool should indicate a vehicle speed whenever the drive wheels are turning.

A faulty or misadjusted Park/Neutral (P/N) switch can result in a false Code 24. Use a Tech 1 "Scan" tool and check for proper signal while in drive. See chart C-1A for P/N switch diagnosis check. Testing and Inspection

If all OK, - Intermittent Malfunctions