CM2150 Electronic Control System – 019-325   Tachograph Circuit

General Information

TOC

The ECM can supply an output signal to operate the vehicle tachograph. The circuit consists of the tachograph signal wire and the common switch return (-) wire.

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

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Resistance Check

TOC

 CAUTION 

To reduce the possibility of pin and connector damage, use test lead, Part Number 3822758, when taking a measurement.

Disconnect the 50-pin OEM harness connector from the ECM connector.

Disconnect the tachograph from the OEM harness.

Set the multimeter to measure resistance.

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Insert one of the test leads into the tachograph signal pin of the 50-pin OEM harness connector. Connect the alligator clip to the multimeter probe.

Insert the other test lead into the tachograph signal pin of the sensor harness connector, and connect the alligator clip to the other multimeter probe. Measure the resistance.

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

If the circuit is not closed, there is an open circuit or the wires in the tachograph connector are reversed. Repair or replace the wire connected to the signal pin in the 50-pin OEM harness connector. Refer to the OEM troubleshooting and repair manual.

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Check for Short Circuit to Ground

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Disconnect the 50-pin OEM harness connector from the ECM connector. Disconnect the tachograph from the OEM harness. Set the multimeter to measure resistance.

Touch the test lead to the tachograph signal pin of the 50-pin OEM harness connector. Touch the other multimeter lead to the engine block. Measure the resistance.

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

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Check for Short Circuit from Pin to Pin

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Disconnect the 50-pin OEM harness connector from the ECM connector. Set the multimeter to measure resistance. Insert a test lead into the tachograph signal pin of the 50-pin OEM harness connector.

Insert the other test lead into the first pin of the 50-pin OEM harness connector, and measure the resistance.

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

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Remove the lead from the first pin and check all other pins, one at a time.

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

If the multimeter does not show an open circuit at any pin, a short circuit exists between the signal pin and any pin that measures less than 100k ohms.

Repair or replace the OEM harness. Refer to the OEM troubleshooting and repair manual.

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Last Modified:  21-Aug-2006