Externally Generated Electronic Interference (Speed Sensor Signals)

Use the following procedures in order to determine if speed sensor signals, generated by a source external to the transmission or wiring harness, are present:

1. Turn the ignition ON.
2. Keep the engine OFF.
3. If the transmission control module (TCM) is ON, install 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. The ignition must be ON in order to use the scan tool to read the speed signals.
4. Read the speed sensor signals.
5. If a speed sensor signal is something other than one (1), there is a short to another circuit that is carrying an AC or pulse width modulated (PWM) signal.
6. Measure the resistance of the sensor.
7. Inspect for shorts to other circuits within the harness or transmission connector.
8. Inspect to ensure there is no conductive material inside the connector.
9. Inspect to ensure the speed sensor circuit wires are a twisted pair.
10. Inspect to ensure a properly grounded drain wire.
11. Inspect for the presence of a strong external AC signal.
12. Repair or replace parts as required.