CM850 Electronic Control System – 019-409   Transmission Shift Modulation Signal Circuit

Disconnect the transmission shift modulator from the OEM harness.

Disconnect the OEM harness connector from the ECM connector.

Check the transmission shift modulator and harness connector for broken, bare, or melted wires; loose, dirty, damaged, or missing pins; and other visible signs of damage.

CAUTION  The leads must fit tightly in the connector without expanding the pins in the connector otherwise the connector will be damaged.

Disconnect the OEM harness connector from the ECM connector. Disconnect the transmission shift modulator from the OEM harness. Set the multimeter to measure resistance.

Insert a test lead into the transmission shift modulator signal pin of the OEM harness connector. Connect the alligator clip to a multimeter probe. Insert the second test lead to the signal pin of the transmission shift modulator harness connector and connect the clip to the other multimeter probe. Measure the resistance.

The multimeter
must show a measurement of 10 ohms or less (closed circuit).

If the measured value is more than 10 ohms, there is an open circuit in the signal wire. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

Repeat the resistance check for the return wire. Measure the resistance from the transmission shift modulator return pin of the OEM harness connector to the transmission shift modulator return pin of the harness connector.

The multimeter
must show a measurement of 10 ohms or less (closed circuit).

If the measured value is more than 10 ohms, there is an open circuit in the return wire. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

Disconnect the OEM harness connector from the ECM connector. Disconnect the transmission shift modulator from the OEM harness. Set the multimeter to measure resistance.

Insert the test lead into the transmission shift modulator signal pin of the OEM harness connector. Touch the other multimeter probe to engine block ground. Measure the resistance.

The multimeter
must show a measurement of 100k ohms or more (open circuit).

If the measured value is less than 100k ohms, there is a short circuit to ground in the signal wire. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

Repeat the short to ground check for the return wire. Measure the resistance from the transmission shift modulator return pin of the OEM harness connector to engine block ground.

The multimeter
must show a measurement of 100k ohms or more (open circuit).

If the measured value is less than 100k ohms, there is a short circuit to ground in the return wire. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

Disconnect the OEM harness connector from the ECM connector. Disconnect the transmission shift modulator from the OEM harness. Set the multimeter to measure resistance.

Measure the resistance from the transmission shift modulator signal pin in the OEM harness connector to all other pins in the connector.

The multimeter
must show a measurement of 100k ohms or more (open circuit).

If the measured value is less than 100k ohms, there is a short circuit between the signal wire and any other pin that measured a closed circuit. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

Disconnect the OEM harness connector from the ECM connector. Disconnect the transmission shift modulator from the OEM harness.

Set the multimeter to measure VDC. Turn the keyswitch to the ON position.

Insert the test lead connected to the positive (+) multimeter probe into the transmission shift modulator signal pin of the OEM harness connector. Touch the negative (-) multimeter probe to engine block ground and measure the voltage.

The voltage
must be 5.5-VDC or less.

If the voltage is incorrect, there is a short circuit from the signal wire to an external voltage source. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

Repeat the short to external voltage source check for the return wire. Measure the voltage from the transmission shift modulator return pin of the OEM harness connector to engine block ground.

If voltage is present, there is a short circuit from the return wire to an external voltage source. Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.