DTC 24

Code 24 - Vehicle Speed Sensor (VSS) Circuit:

Wiring Diagram For Code 24 - Vehicle Speed Sensor (VSS) Circuit:

CODE 24 - VEHICLE SPEED SENSOR (VSS) 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".

"Scan" reading should closely match with speedometer reading with drive wheels turning. To prevent misdiagnosis, the technician should identify the type of Vehicle Speed Sensor (VSS) used prior to using this chart. Disregard a Code 24 set when drive wheels are not turning.


Test Description: Numbers below refer to circled numbers 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.

Disregard Code 24 that sets when drive wheels are not turning.

2. 8-12 volts, at the I/P connector, indicates CKT 437 is open between the I/P connector and the 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 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 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. A faulty or misadjusted Park/Neutral (P/N) switch can result in a false Code 24. "Scan" tool and check for proper signal while in drive. Refer to CHART C-1A for P/N switch diagnosis check.

See Diagnosis By Symptoms - No Trouble Codes Stored.