With 4L60 Automatic Transmission

Code 24 VSS Circuit Fault:

Wiring Diagram For Code 24 VSS Circuit Fault:

CODE 24 - VSS CIRCUIT FAULT


CIRCUIT DESCRIPTION:

The ECM applies and monitors 12 volts on CKT 437. CKT 437 connects to the DRAC, which alternantely grounds CKT 437, when receiving voltage pulses from Vehicle Speed Sensor (VSS) when drive wheels are turning. This pulsating action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between pulses.

A "Scan" tool 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:

^ CKT 437 voltage is constant.
^ Engine speed is more than 1200 rpm .
^ Vehicle speed signal indicates less than 2 mph on scanner.
^ All conditions must be met for 5 seconds. These conditions are met during a road load deceleration.

2. This test determines if the DRAC is receiving the A/C signal from the VSS.

3. This test monitors the DRAC voltage on CKT 437. With the wheels turning, the pulsating actioning will result in a varying voltage. The variation will be greater at low wheel speeds to an average of 4-6 volts at about 20 mph.



DIAGNOSTIC AIDS:

1. "Scan" reading should closely match with speedometer reading, with drive wheels turning.

2. Check park/neutral switch diagnosis chart if vehicle equipped with automatic transmission.

3. If park/neutral switch is OK, SEE DIAGNOSIS BY SYMPTOM - NO TROUBLE CODES STORED.