Did you perform the Instrument Cluster Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - Instrument Cluster

1. With a scan tool select Powertrain, Data Display, Engine Data Display, and Data in order to monitor the engine speed.
2. Start the engine.
3. Compare the engine speed on the scan tool to the engine speed displayed on the tachometer.

Does the scan tool agree with the tachometer?

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Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

1. Test the tachometer signal circuit at the instrument cluster by backprobing with a digital multimeter (DMM). Refer to Instrument Cluster Replacement .
2. Select the AC Voltage scale then select frequency
3. Measure the frequency between the tachometer signal circuit and a good ground with the engine idling. Refer to Circuit Testing in Wiring Systems.

is the frequency within the specified range?

15-25 HZ at 500-800 RPM

Go to Step 4

Go to Step 5

Replace the instrument cluster. Refer to Instrument Cluster Replacement

Did you complete the replacement?

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Go to Step 7

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Test the tachometer signal circuit for an open, short to ground, or a short to voltage. Refer to Circuit Testing in Wiring Systems.

Did you find and correct the conditions?

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Go to Step 7

Go to Step 6

Important: Program the replacement PCM/VCM.

Replace the PCM/VCM. Refer to Powertrain Control Module Replacement in Engine Controls - 4.3L or VCM Replacement/Programming in Engine Controls - 4.8L, 5.3L, 6.0L.

Did you complete the replacement?

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Go to Step 7

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Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 3