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Electronic Control System Signature, ISX and QSX15 Engines – 019-083   Tachometer Circuit

General Information

 TOC

The ECM can supply an output signal to operate the vehicle tachometer.

The circuit is wire No. 11 (the output signal) and a tachometer internal ground in the OEM harness.

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Resistance Check

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Disconnect the OEM harness from the ECM. Disconnect the tachometer from the OEM harness.

 CAUTION 

Do not use probes or leads other than Part No. 3822758. The connector will be damaged. The leads must fit tightly in the connector without expanding pins in the connector.

Insert the test lead into pin 11 of the OEM harness connector and connect it to the multimeter probe.

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Locate the tachometer connector of the OEM harness.

Connect the other lead to the multimeter probe and connect it to the connector terminal of the tachometer that is coming from the engine ECM. Consult the OEM troubleshooting and repair manual for wiring schematics.

Adjust the multimeter to the resistance setting. 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 11 in the OEM harness according to the vehicle manufacturer’s procedures.

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Check for Short Circuit to Ground

 TOC

Disconnect the tachometer from the OEM harness.

Insert the test lead into pin 11 of the harness connector and connect it to the multimeter probe. Touch the other multimeter probe to the engine block ground. Measure the resistance.

The multimeter

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

If the circuit is

not open in either of the prior checks, repair the wires which have incorrect readings. Refer to the OEM troubleshooting and repair manual for the repair procedures.

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Check for Short Circuit from Pin to Pin

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Disconnect the tachometer from the OEM harness. Insert the test lead into pin 11 of the OEM harness connector and connect it to the multimeter probe. Insert the other lead into pin 10 of the OEM harness connector, connect it to the other multimeter probe, and measure the resistance.

The multimeter

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

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Remove the test lead from pin 10 and measure the resistance from pin 11 to all other pins in the OEM harness connector.

The multimeter

must show an open circuit (100k ohms or more) at all pins. If any pin-to-pin check measures as

not open, there is a short circuit between pin 11 and any other pin that measured a closed circuit. Repair or replace the OEM harness. Refer to Procedure

019-250 for harness repair or Procedure

019-071 for harness replacement.

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Last Modified:  21-Jan-2003
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Published by Jack

Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.