Cummins ISX11.9 CM2250 – Service Manual 019-087   Unswitched Battery Supply Circuit

The electronic control module (ECM) receives constant voltage from the batteries through the ECM battery supply positive (+) wire that is connected directly to the positive (+) battery post. There is one in-line 30-ampere fuse in the ECM supply wire to protect the ECM. The ECM receives switched battery input through the keyswitch input signal when the vehicle keyswitch is turned ON. The ECM battery supply negative (-) wire is connected directly to the negative (-) battery post.

The ECM battery supply positive (+) wire and the ECM battery supply negative (-) wire are in the ECM power harness.

Always check the ECM battery supply fuse when troubleshooting the ECM and power supply circuit.

Check the battery voltage. Refer to Procedure 019-008 in Section 19.

Disconnect the ECM power harness connector from the ECM.

Adjust the multimeter to measure resistance.

Insert a test lead into the ECM battery supply negative (-) pin of the OEM harness connector. Attach it to a multimeter probe.

Touch the other multimeter probe to the engine block ground and measure the resistance.

The multimeter must show 10 ohms or less.  Repeat this for all ECM battery supply negative (-) pins in the OEM harness connector.

If the resistance value is not correct, check the OEM harness battery supply negative (-) circuit.

Repair or replace the OEM harness. Refer to Procedure 019-071 in Section 19.

When the checks have been completed, connect the OEM harness connector.

Check the battery voltage supply at the ECM battery supply positive (+) pin of the OEM harness connector.

Turn the keyswitch to the OFF position. Disconnect the OEM harness connector from the ECM. Set the multimeter to measure VDC.

Measure the voltage from the ECM battery supply positive (+) to ground.

The voltage must read battery voltage at this pin.

If the voltage is not correct, repair or replace the ECM power harness.

Repeat this step for all battery supply positive (+) pins in the OEM harness connector.