ISB/ISBe Series Engines – 019-087   Unswitched Battery Supply Circuit

The ECM receives constant voltage from the batteries through the unswitched battery wires that are connected directly to the positive (+) battery post. There is either one 30-amp or two 15-amp fuses in the unswitched battery wires to protect the ECM. The ECM receives switched battery input through the vehicle keyswitch wire when the vehicle keyswitch is turned on. The battery return wires are connected directly to the negative (-) battery post.

The unswitched battery wires and the battery return wires are in the OEM harness.

Always check the unswitched battery supply fuse or fuses when troubleshooting the ECM power supply circuits.

Disconnect the OEM harness 89-pin connector from the ECM. Lift the connector lever and pull the connector from the ECM.

Check the unswitched battery supply wires in the OEM harness for proper connection. Disconnect the OEM harness from the ECM. Check for damaged pins in the ECM and the OEM harness connector. The unswitched battery supply pins are: 1, 7, 12, and 13.

CAUTION  To reduce the possibility of damage to the connector pins, do not use probes or leads other than Part Number 3164110. The OEM harness will be damaged. The leads must fit tightly in the harness without expanding the pins of the connector.

Set the multimeter to measure resistance.

Insert one multimeter probe on pins 1, 7, 12, and 13 of the OEM harness connector. Touch the other multimeter probe to the positive (+) battery terminal, and measure the resistance.

The multimeter

must show 10 ohms or less.

Then, repeat the check as follows. Touch the multimeter probe with attached lead to pins 3, 9, 14, and 15 of the OEM harness connector. Touch the other multimeter probe to the negative (-) battery terminal, and measure the resistance.

The multimeter

must show 10 ohms or less.

If the resistance value is

not correct, check the batteries, cables, and cable connections. Repair or replace the parts as required.

If more than 10 ohms are measured in any check, there is an open circuit. Repair or replace the OEM harness.

Refer to Procedure

019-323
or

019-071.

After completing the checks, reconnect the 89-pin OEM harness connector to the ECM.

Disconnect the OEM harness 89-pin connector from the ECM. Lift the connector level and pull the connector from the ECM.

Check the unswitched battery supply wires in the OEM harness for proper connection. Disconnect the harness from the ECM. Check for damaged pins in the ECM and the harness. The unswitched battery supply pins are 1, 7, 12, and 13.

CAUTION  To reduce the possibility of damage to the connector pins, do not use probes or leads other than Part Number 3164110. The leads must fit tightly in the connector without expanding the pins of the connector.

Set the multimeter to measure resistance.

Insert one test lead connected to the multimeter probe to pins 1, 7, 12, and 13 of the OEM harness connector. Touch the other multimeter probe to the engine block ground, and measure the resistance. The multimeter

must show 100k ohms or more.

If the resistance value is

not correct, check the batteries, cables, and cable connections. Repair or replace the parts as required.

After completing the checks, reconnect the 89-pin connector to the ECM.

Disconnect the OEM harness 89-pin connector from the ECM.

Check the unswitched battery supply wires in the OEM harness for short circuit from pin to pin. Disconnect the harness from the ECM. Check for damaged pins. The unswitched battery supply pins are 1, 7, 12, and 13.

CAUTION  To reduce the possibility of damage to the connector pins, do not use probes or leads other than Part Numbers 3164110 and 3164112. The leads must fit tightly in the connector without expanding the pins of the connector.

Set the multimeter to measure resistance.

Insert one test lead attached to the multimeter probe to pins 1, 7, 12, and 13 of the OEM harness connector. Measure the resistance to all other pins in the 89-pin connector. The resistance

must be 100k ohms or more on all pins

except 1, 7, 12, and 13.

If the resistance value is

not correct, check the batteries, cables, cable connections, and fuses. Repair or replace the parts as required.

After completing the checks, reconnect the 89-pin OEM harness connector to the ECM.

Disconnect the 89-pin connector from the ECM. Lift the connector lever and pull the connector from the ECM. Inspect for damaged pins in the ECM and OEM harness connectors.

CAUTION  To reduce the possibility of damage to the connector pins, do not use probes or leads other than Part Number 3164110. The leads must fit tightly in the connector without expanding the pins of the connector.

Set the multimeter to measure VDC.

Insert one test lead attached to the multimeter probe to pins 1, 7, 12, and 13 of the OEM harness 89-pin connector. Touch the other multimeter probe to the engine block ground, and measure the voltage. The multimeter

must show battery voltage.

If voltage value is

not correct, check the batteries, cables, and cable connections. Repair or replace the parts as required. Repair or replace the OEM harness. Refer to Procedure

019-323 or

019-071.

After completing the checks, reconnect the 89-pin connector to the ECM.