Test Step 6. Check the ECM Connection to the Tachometer

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TM 9-2320-312-24-2

Troubleshooting Section

Expected Result:

The wires from the ECM to the tachometer are

The "Tachometer Calibration" matches the ECM

undamaged.

tachometer calibration.

Results:

OK The tachometer is correctly calibrated.

OK The wiring is OK. Proceed to Test Step 7.

Not OK The wiring is damaged.

Repair: Perform the following repair:

1. If the tachometer is correctly calibrated but

Repair: Perform the following repair:

the tachometer does not work, replace the

tachometer or send the tachometer to the OEM

Either repair the wiring or send the vehicle to the

dealer for repair.

OEM dealer. Verify that the repair eliminates the

problem.

2. Verify that the repair eliminates the problem.

STOP.

Test Step 7. Check the Tachometer

Battery Supply Voltage.

Not OK The tachometer is not correctly

calibrated.

A. Connect the tachometer lines to the ECM and

Repair: Perform the following repair:

the tachometer.

B. Check the +Battery connections and the -Battery

1. Calibrate the tachometer in order to match

the ECM.

connections to the tachometer. Include the fuses

and the circuit protection.

a. If the tachometer calibration is known and

the tachometer calibration is within 12.0 to

Expected Result:

500.0 pulses per revolution, change the

Customer Programmable Parameter of the

The tachometer is receiving the correct battery

ECM "Tachometer Calibration" in order to

supply voltage.

match the tachometer.

Results:

2. Verify that the repair eliminates the problem.

OK The battery supply voltage is OK.

STOP.

Repair: Perform the following repair:

Test Step 6. Check the ECM Connection

to the Tachometer.

If the tachometer is receiving the correct battery

supply voltage but the tachometer does not work,

A. Find the tachometer signal connections to the

replace the tachometer or send the tachometer to

tachometer.

the OEM dealer for repair.

B. Disconnect the wires from the ECM to the

STOP.

tachometer at the ECM connector and at the

tachometer.

Not OK The battery supply voltage is incorrect.

Refer to Illustration 177.

Repair: Perform the following repair:

C. Check for continuity through the wires to the

1. Repair the wiring for the battery supply.

ECM connector P1:39 (Tachometer-) and P1:38

(Tachometer+).

2. Verify that the repair eliminates the problem.

Note: Some of the tachometers require only one

STOP.

signal line to be connected. Either of the ECM

terminals can be used for this type of tachometer.

The other wire should be left disconnected. If both

wires are connected, and one indicates an open

circuit, repair this line.