Externally Generated Electronic Interference (Speed Sensor Signals)

Externally Generated Electronic Interference (Speed Sensor Signals)
Use the following procedures to determine if speed sensor signals generated by a source external to the transmission or wiring harness are present:

1. Turn ignition ON.
2. Keep engine OFF.
3. If the TCM is ON, connect the scan tool.

Important: If false speed signals were present at the previous shutdown, the TCM might still be ON even though the ignition is OFF. The scan tool is powered by ignition power so the ignition must be ON to use the scan tool to read the speed signals.

4. Read speed sensor signals.
5. If a speed sensor signal is other than one (1), then there is a short to another circuit that is carrying an AC or PWM signal.
6. Check the resistance of the sensor.
7. Check for shorts to other circuits within the harness or transmission connector.
8. Check to ensure there is no conductive material inside the connector.
9. Check to be sure a there the speed sensor circuit wires are a twisted pair.
10. Check to ensure a properly grounded drain wire.
11. Check for the presence of a strong external AC signal.
12. Repair or replace parts as required.