Item 7 Output Speed Sensor

While vehicle is in park and engine idling, check the output speed sensor on the DRB III(R). If the TCM indicates an output speed greater than zero RPM, the speed sensor, TRS, or thermistor may be picking up electrical noise from the wiring harness or there is an intermittent ground problem. It is important to note that the thermistor uses the same ground circuit as the speed sensor. Follow wiring harness check described in DTC Tests 56, 57 and 58 to help with further diagnosis. Also, see TSB 08-07-94 Rev. B.

Intermittent noise may cause reverse block logic to be activated. Look for output speed during a park to reverse shift. If output speed noise exceeds 400 RPM, reverse block logic will be activated. If the electrical noise is continuous, reverse block logic will exist until the condition is repaired. If the condition is intermittent, or has been fixed, the output speed reading may be latched above 400 RPM. This will prevent a shift into reverse until the shifter is cycled to overdrive and back into reverse.