Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information
Special Tools
* EL-49742 - Battery Voltage B+ and Ground Source Harness
* J 35616 - GM-Approved Terminal Test Kit
Circuit/System Verification
1. Raise and support the drive wheels.
2. Start and idle the engine.
3. Place the transmission in DRIVE.
4. Monitor VSS on the scan tool under engine data.
5. The VSS on the scan tool should be greater than 100 RPM.
Circuit/System Testing
1. Key OFF. Let sit for 2 minutes to ensure that the ECM shuts down.
2. Disconnect the X1 connector from the VSS. Using the J 35616-2A GY probes, test for less than 0.1 V between the following circuits and a
good ground.
* VSS high signal circuit, VSS harness X1 pin A.
* VSS low signal circuit, VSS harness X1 pin B.
锟斤拷If the voltage is greater than the specified value, test the affected circuit for a short to voltage. If all circuits and connections test
normal, test the ECM for proper operation.
3. Key ON, engine OFF. Test for a diagnostic 2-3 V (low current) between the following circuits and a good ground.
* VSS high signal circuit, VSS harness X1 pin A.
* VSS low signal circuit, VSS harness X1 pin B.
锟斤拷If the voltage is less than the specified value, test the affected circuit for an open/high resistance, short to ground or short together. If
all circuits and connections test normal, test the ECM for proper operation.
锟斤拷If the voltage is greater than the specified value, test the affected circuit for a short to voltage. If all circuits and connections test
normal, test the ECM for proper operation.
4. Test the VSS for proper operation.
Component Testing
VSS
1. Key OFF.
2. Disconnect the X1 connector from the VSS. Using the J 35616-3 GY probes, test for 1200-2140 ohm between the VSS high signal circuit,
VSS pin A, and the VSS low signal circuit, VSS pin B.
锟斤拷If the resistance is outside the specified value, replace the VSS.
3. Test for greater than 10 M ohm between the following circuits and a good ground.
* VSS high signal circuit, VSS pin A.
* VSS low signal circuit, VSS pin B.
锟斤拷If the resistance is below the specified value, Replace the VSS.
4. Block the front wheels. Raise and support the driver's side rear wheel. While rotating the raised wheel by hand, test for greater than 0.4 V AC
between the VSS high signal circuit, VSS pin A, and the VSS low signal circuit, VSS harness pin B. The passenger side rear wheel takes
more effort to turn. If both drive wheels are raised and unblocked, twice the effort will be required to reach 0.4 V AC. If the vehicle is
sufficiently supported to safely place the transmission in neutral, less effort will be required to turn the raised wheel.
锟斤拷If the AC voltage is below the specified value, replace the VSS.
ECM
1. Remove key from the ignition. Let sit for 2 minutes to ensure ECM shut down
2. Disconnect the X1 connector from the ECM. Using the J 35616-64B L-BU probes, test for 1200-2140 ohm between the VSS high signal
circuit, ECM X1, pin 71 and the VSS low signal circuit, ECM X1, pin 72.
锟斤拷If the resistance is below the specified value, test the affected circuits for being shorted together. If all circuits and connections test
normal, test the VSS for proper operation.
锟斤拷If the resistance is above the specified value, test the affected circuits for open/high resistance condition. If all circuits and connections
