Electronic Control System Gas Plus Engines – 019-087   Unswitched Battery Supply Circuit

The ECM receives constant voltage from the batteries through the switched battery wires that are connected directly to the positive (+) battery post. There are four in-line fuses in each of the unswitched battery wires to protect the ECM. The ECM receives switched battery input through the keyswitch wire, when the 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 engine harness and the OEM harness.

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

Disconnect the engine harness from the OEM harness at the 23-pin connector.

Loosen the locking collar and separate the connector.

Set the multimeter to measure resistance. Insert a test lead into one of the unswitched battery supply pins in the 23-pin OEM connector, OEM side. Touch the other multimeter probe to the battery positive (+) terminal, and measure the resistance.

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

Repeat the resistance check from each unswitched battery supply pin in the 23-pin connector to the battery positive (+) terminal.

If the resistance value is not correct, check the batteries, cables, OEM harness, and cable connections. Repair or replace the parts as required.

After completing the checks, connect the 23-pin connector.

Check the battery supply wires in the engine harness for proper resistance.

Disconnect engine harness ECM 1 connector from the ECM.

Check for damaged pins in the ECM and the harness connectors.

Insert a test lead into one of the unswitched battery supply pins in the 50-pin ECM connector. Touch the other multimeter probe to the battery positive (+) terminal, and measure the resistance.

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

Repeat the resistance check from each unswitched battery supply pin in the 50-pin ECM connector to the battery positive (+) terminal.

If the multimeter shows a measurement of more than 10 ohms in either of the previous resistance checks, there is an open circuit in the engine harness.

Repair or replace the engine harness. Refer to Procedure 019-204 or 019-043.

Disconnect the engine harness from the OEM harness at the 23-pin connector.

Loosen the locking collar and pull the connector apart.

Set the multimeter to measure resistance. Insert a test lead into one of the unswitched battery supply pins in the 23-pin OEM connector, OEM side. Touch the other multimeter probe to the engine block, and measure the resistance.

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

Repeat the resistance check from each unswitched battery supply pin in the 23-pin connector to ground.

If the resistance value is not to specification, repair or replace the OEM harness.

Refer to the OEM manual.

After completing the checks, connect the 23-pin connector.

Check the battery supply wires in the engine harness for a short circuit to ground.

Disconnect the engine harness ECM 1 connector from the ECM.

Check for damaged pins in the ECM and the harness connectors.

Insert a test lead into one of the unswitched battery supply pins in the 50-pin ECM connector. Touch the other multimeter probe to engine block ground, and measure the resistance.

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

Repeat the resistance check from each unswitched battery supply pin in the 50-pin ECM connector to ground.

If the multimeter shows a measurement of less than 100k ohms in either of the previous resistance checks, there is a short circuit in the engine harness.

Repair or replace the engine harness. Refer to Procedure 019-204 or 019-043.

Disconnect the engine harness from the OEM harness at the 23-pin connector.

Loosen the locking collar and separate the connector.

Set the multimeter to measure resistance. Insert a test lead into one of the unswitched battery supply pins in the 23-pin OEM connector, OEM side. Touch the other test lead to all other pins in the connector, and measure the resistance at each pin.

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

Repeat the resistance check from each unswitched battery supply pin in the 23-pin connector to all other pins in the connector.

If the resistance value is not to specification, repair or replace the OEM harness.

Refer to the OEM manual.

After completing the checks, connect the 23-pin connector.

Check the battery supply wires in the engine harness for a short circuit from pin to pin.

Disconnect engine harness ECM connectors 1 and 2 from the ECM.

Check for damaged pins in the ECM and the harness connectors.

Insert a test lead into one of the unswitched battery supply pins in the 50-pin ECM connector 1. Touch the other test lead to all other pins in connector 1, and measure the resistance. Then, repeat check from the unswitched battery supply pin in connector 1 to all pins in connector 2.

The multimeter must show a measurement of 100k ohms or more (open circuit) at all pins in both ECM connectors.

Repeat the resistance check from each unswitched battery supply pin in the 50-pin ECM connector to all pins in engine harness ECM connectors 1 and 2.

If the multimeter shows a measurement of less than 100k ohms in either of the previous resistance checks, there is a short circuit from pin to pin in the engine harness.

Repair or replace the engine harness. Refer to Procedure 019-204 or 019-043.

Disconnect the engine harness from the OEM harness at the 23-pin connector.

Loosen the locking collar and pull the connector apart.

Set the multimeter to measure VDC. Turn the keyswitch to the ON position. Insert a test lead into one of the unswitched battery supply pins in the 23-pin OEM connector, OEM side. Touch the other multimeter probe to the engine block and measure the voltage.

The multimeter must show a measurement of battery voltage.

Repeat the voltage check from each unswitched battery supply pin in the 23-pin connector to ground.

If the voltage value is not to specification, check batteries, cables, and cable connections. Repair or replace the parts as required. If the batteries, cables, and connections are okay, and voltage value is not to specification, repair or replace the OEM harness.

Refer to the OEM manual.

After completing the checks, connect the 23-pin connector.

Check the battery supply wires in the engine harness for proper grounding.

Disconnect engine harness ECM connector 1 from the ECM.

Check the engine harness and ECM connectors for damaged pins.

Set the multimeter to measure VDC. Turn the keyswitch to the ON position. Insert a test lead into one of the unswitched battery supply pins in the 50-pin ECM connector. Touch the other multimeter probe to the engine block and measure the voltage.

The multimeter must show a measurement of battery voltage.

Repeat the voltage check from each unswitched battery supply pin in the 50-pin ECM connector to ground.

If battery voltage is not measured in any check, there is an open circuit. If the circuit has been checked for proper connection in the OEM harness, repair or replace the engine harness. Refer to Procedure 019-204 or 019-043.