Electronic Control System Gas Plus Engines – 019-357   Humidity Sensor Circuit

Disconnect engine harness ECM connectors 1 from the ECM. Disconnect the humidity sensor from the engine harness. Set the multimeter to measure resistance.

Measure the resistance from the humidity sensor +5 VDC supply pin in engine harness ECM connector 1 to the corresponding pin in the engine harness sensor connector.

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

If the circuit is not closed, there is an open circuit in the supply wire.

Repair or replace the engine harness. Refer to Procedure 019-205, 019-204, or 019-043.

Measure the resistance from the humidity sensor return pin in engine harness ECM connector 1 to the corresponding pin in the engine harness sensor connector.

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

If the circuit is not closed, there is an open circuit in the return wire. Repair or replace the engine harness. Refer to Procedure 019-205, 019-204, or 019-043.

Measure the resistance from the humidity sensor signal pin in engine harness ECM connector 1 to the corresponding pin in the engine harness sensor connector.

The multimeter must show a closed circuit (10 ohms or less) for both checks.

If either circuit is not closed, there is an open circuit in the applicable signal wire. Repair or replace the engine harness. Refer to Procedure 019-205, 019-204, or 019-043.

Disconnect engine harness ECM connectors 1 from the ECM. Disconnect the humidity sensor from the engine harness. Set the multimeter to measure resistance.

Measure the resistance from the humidity sensor return pin in engine harness ECM connector 1 to engine block ground.

The multimeter must show an open circuit (100k ohms or more).

If the circuit is not open, there is a short circuit to ground in the return wire.

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

Measure the resistance from the humidity sensor signal pin in engine harness ECM connector 1 to engine block ground.

The multimeter must show an open circuit (100k ohms or more) for both signal wire checks.

If the circuit is not open, there is a short circuit to ground in the applicable signal wire. Repair or replace the engine harness. Refer to Procedure 019-204, or 019-043.

Measure the resistance from the humidity sensor +5 VDC supply pin in engine harness ECM connector 1 to engine block ground.

The multimeter must show an open circuit (100k ohms or more).

If the circuit is not open, there is a short circuit to ground in the supply wire. Repair or replace the engine harness. Refer to Procedure 019-204, or 019-043.

Disconnect engine harness ECM connectors 1 and 2 from the ECM. Disconnect the humidity sensor from the engine harness. Set the multimeter to measure resistance.

Measure the resistance from the humidity sensor signal pin in engine harness ECM connector 1 to all other pins in the connector and to all pins in engine harness ECM connector 2.

The multimeter must show an open circuit at all pins.

If any pin-to-pin check does not show an open circuit, there is a short circuit between the applicable pins.

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