Refer to Engine Controls Schematic
I/P, Generator and Driver Information Display
Circuit Description
The PCM supplies the ground to energize the Instrument Cluster tachometer. When the ignition switch is first turned ON the PCM grounds the tachometer circuit. The circuit will remain grounded until the PCM receives the first 24X reference pulse. Once the 24X reference pulse is received, the PCM controls the pulse frequency in relationship to engine RPM. The tachometer is controlled at a rate of two pulses per crankshaft revolution.
Diagnostic Aids
Refer to Instrument Cluster System Check in Instrument Panel, Gauges and Console for additional diagnostic information.
Check for the following conditions:
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Poor terminal connection. |
| Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Wiring Systems for diagnosis and repair. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Systems for diagnosis and repair. |
| • | Inspect the PCM and the engine grounds for clean and secure connections. |
If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.
Test Description
Numbers below refer to the step numbers on the Diagnostic Table:
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Normally, ignition feed voltage should be present on the output driver circuit with the PCM disconnected and the ignition turned on.
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Test for a shorted component or a short to battery positive voltage on the output driver circuit. Either condition would result in a measured current of over 0.5 amps.
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Tests for a faulty instrument cluster.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Instrument Cluster System Check? | -- | Go to Instrument Cluster System Check in Instrument Panel, Gauges and Console | |||||
2 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||||||
Is the voltage near the specified value? | B+ | |||||||
Does the current reading remain less than the specified value? | 0.5 Amp | |||||||
Is the voltage at the specified value? | 0.0V | |||||||
6 | Locate and repair short to voltage in the tachometer control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |||||
7 | Inspect the ignition feed fuse for the instrument cluster. Is the fuse open? | -- | ||||||
8 |
Did you complete the repair? | -- | -- | |||||
9 |
Is the voltage near the specified value? | B+ | ||||||
10 | Test the tachometer control circuit for an open or a short to ground. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||
11 | Test the tachometer control circuit and the ignition feed circuit for a poor connection at the instrument cluster and at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Was a problem found? | -- | ||||||
12 | Inspect for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Was a problem found? | -- | ||||||
13 | Inspect the tachometer control circuit for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | ||||||
14 | Locate and repair open in ignition feed circuit to the instrument cluster. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |||||
15 | Replace the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console. Did you complete the repair? | -- | -- | |||||
|
Important: : Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the repair? | -- | -- | ||||||
17 | Operate the vehicle while observing the I/P tachometer. Does the I/P tachometer operate properly? | -- | System OK | Go to Instrument Cluster System Check in Instrument Panel, Gauges and Console |
