For 1990-2009 cars

## Tachometer Inaccurate or Inoperative L18 8.1L Gasoline Engine

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Instrument Cluster Schematics
1 | Did you perform the Instrument Cluster Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Instrument Cluster
2 |

1. Install a scan tool.
2. Start the engine.
3. With the scan tool, observe the Engine Speed parameter in the PCM Engine Data 1 data list.

Does the Engine Speed parameter match the tachometer display?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3 |

1. Turn the ignition OFF.
2. Disconnect the PCM connector C2.
3. Turn the ignition ON, with the engine OFF.
4. Measure the voltage from the engine speed signal circuit to a good ground.

Does the voltage measure greater than the specified value?

9.0 V

Go to Step 5

Go to Step 4

4 | Test the engine speed signal circuit for an open, or for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 6
5 | Test the engine speed signal circuit for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 7
6 | Inspect for poor connections at the harness connector of the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8
7 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9
8 | Replace the IPC. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 10 | --
9 | Important: Program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 8.1L. Did you complete the replacement? | -- | Go to Step 10 | --
10 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2

## Tachometer Inaccurate or Inoperative LG5 7.2L Diesel Engine

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Instrument Cluster Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Instrument Cluster
2 |

1. Disconnect the generator connector.
2. Start the engine.
3. Using a J 39200 DMM, measure the DC voltage at the Generator Output Tachometer Pulse signal circuit of the generator to a good ground.

Does the generator voltage measure at or near the specified value?

7.5 V

Go to Step 3

Go to Charging System Test in Engine Electrical

3 |

1. Disconnect the instrument cluster connector and C200.
2. Connect a test lamp between the IPC harness connector engine speed signal circuit and battery voltage.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 7

4 | With the test lamp connected at the same location from the previous step, disconnect the MFAM. Does the test lamp still illuminate? |  | Go to Step 5 | Go to Step 10
5 | With the test lamp connected at the same location from the previous step, disconnect the hourmeter. Does the test light still illuminate? |  | Go to Step 6 | Go to Step 11
6 | Test the engine speed signal circuit for a short to ground between the instrument cluster and C200. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8
7 | Test the engine speed signal circuit for an open, or for a high resistance between the instrument cluster and C200. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8
8 | Test the engine speed signal circuit for an open, for a high resistance, or for a short to ground between the generator and C200. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9
9 | Replace the IP cluster. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
10 | Replace MFAM. Refer to Multifunction Alarm Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
11 | Replace Hourmeter. Refer to Engine Hour Meter Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
12 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | --