Code 39

CIRCUIT DESCRIPTION
The transmission speed sensor provides information on vehicle speed to the TCM. The speed sensor is a magnetic inductive pickup. The sensor is mounted above a toothed target wheel in the transmission extension. The toothed target wheel is connected to the transmission output shaft. As the output shaft turns, the target wheel teeth induce a variable voltage in the magnetic pickup. As a result, the sensor sends an alternating current (AC) signal to the TCM. The signal is proportional to vehicle speed. As the vehicle moves faster, the signal alternates faster between positive and negative voltages.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. This test checks the continuity of circuit wiring and transmission speed sensor.
2. This test determines if terminal 20 of the TCM connector is shorted to ground.
3. This test checks the continuity of the trans mission speed sensor.

DIAGNOSTIC AIDS
Trouble Code 39 sets when the TCM detects an open at terminals 20 or 14. Code may also set if the mode switch is misadjusted when selector is in neutral. If so, the mode switch must be adjusted before continuing diagnosis. Tech-1 should indicate a vehicle speed whenever the drive wheels are turning. If the wire to terminal 14 is shorted to voltage, the TCM will also be damaged. A misadjusted mode switch when selector is in N range may be detected by Diagnostic Trouble Code 39. Mode switch must be adjusted before continuing of diagnosis.

CIRCUIT DIAGRAM

Trans. Speed Sensor Circuit:

CODE 39 DIAGNOSTIC CHART

Code 39 Diagnostic Chart: