Illustration 174 Schematic No. 1 for tachometer

400

TM 9-2320-312-24-2

Troubleshooting Section

The most likely source of a tachometer circuit

problem is the vehicle wiring. The second most

likely source of a tachometer circuit problem is

the tachometer and the least likely source of a

tachometer circuit problem is the ECM.

Note: A tachometer may also be driven by the SAE

J1587 Data Link. If the engine ECM communicates

with the electronic service tool and the instrument

cluster uses the signal from the SAE J1587 data

link, the problem is in one of two locations. Either

the problem is in the wiring from the ECM to the

dash, or the problem is in the dash. The vehicle

should be referred to the OEM dealer for service.

Note: Do not disturb the camshaft position sensor

and the crankshaft position sensor in order to

troubleshoot a tachometer circuit problem. If there is

a problem that is associated with the sensors, refer

to Troubleshooting, "Engine Speed/Timing Sensor

Circuit - Test". Any problem that is associated with

the camshaft position sensor and the crankshaft

position sensor will be apparent because of engine

operation with a diagnostic code that is present.

There are no diagnostic codes that are associated

with the tachometer circuit.

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Illustration 174

Schematic No. 1 for tachometer

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Illustration 175

Schematic No. 2 for tachometer