ISB/ISBe Series Engines – 019-083   Tachometer Circuit

The ECM can supply an output signal to operate the vehicle tachometer. The highside output is wire number 37, referenced to ground. The lowside output is wire number 49, referenced to battery voltage.

Refer to the OEM troubleshooting and repair manual for troubleshooting instructions.

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

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

Locate the tachometer connector of the OEM harness.

Insert a test lead attached to the multimeter probe to the connector terminal at the tachometer that is coming from the engine ECM. Consult the equipment manufacturer’s repair manual for wiring schematics.

Set the multimeter to measure resistance, and measure the resistance.

The multimeter must show a closed circuit (10 ohms or less). If the circuit is not closed, there is an open circuit or the wires in the tachometer connector are reversed. Repair or replace the wire connected to pin 37 or 49 in the 89-pin OEM harness connector. Refer to Procedure 019-071.

Disconnect the tachometer from the OEM harness.

Insert the test lead into pin 37 of the OEM harness connector. Touch the other multimeter probe to the engine block. Measure the resistance.

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

Repeat the procedure for pin 49, if applicable.

If the circuit is not open, repair or replace the OEM harness. Refer to Procedure 019-071.

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.

Insert the test lead into pin 37 or 49 of the OEM harness connector. Insert the other lead into pin 1 of the connector, and measure the resistance.

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

Remove the lead from pin 1 and check all other pins. Measure the resistance. The multimeter must show an open circuit (100k ohms or more)
at all pins. If the multimeter does not show an open circuit at any pin, a short circuit exists between pin 37 or 49 and any pin that reads less than 100k ohms.

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