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 overall function of VSS circuit:
- Using Scan Tool
Raise drive wheels and support vehicle. Start engine. Ensure TCS switch is in OFF position. Select MODE 1 on scan tool and read VSS signal. Shift transmission into Drive and let drive wheels rotate. VSS signal should be able to exceed 6 MPH. - Using MIL
Raise drive wheels and support vehicle. Start engine. Ensure TCS switch is in OFF position. Using an oscilloscope, measure voltage between ground and ECM terminal No. 68 by backprobing. See Figure and Figure . Shift transmission into Drive and let drive wheels rotate. VSS signal should be as shown. See PIN VOLTAGE CHARTS article.
CAUTION:
DO NOT use ECM ground terminals when measuring voltage.