DTC Confirmation Test (Overall Function Check)
NOTE:
Use the following test to check overall function of VSS circuit. During this test, DTC may not be confirmed.
Malfunction is detected when zero MPH signal is sent to ECM while vehicle is moving. Possible causes are:
- VSS circuit open or shorted.
- Defective VSS.
Depending on equipment available, use one of the following to check function of VSS circuit:
- Using Scan Tool
Raise drive wheels and support vehicle. Start engine. With transmission in a forward gear and wheels turning at 6 MPH, select MODE 1 and check VSS output signal. VSS output signal should be 6 MPH. - Using MIL
Raise drive wheels, and support vehicle. Connect an oscilloscope between ground and ECM terminal No. 26 by backprobing. See Figure. Start engine. Shift transmission into a forward gear. Increase engine speed until drive wheels are rotating at 25 MPH. VSS signal should be as shown. See Fig 1.