Circuit Description
The engine control module (ECM) creates the vehicle speed signal by pulsing the signal circuit to ground at a rate of 4K PPM. The instrument panel cluster (IPC) converts the 4K PPM signal to a speedometer position. The IPC also receives a class 2 message from the ECM indicating the vehicle speed. The IPC uses this class 2 message for diagnostic purposes.
Conditions for Running the DTC
| • | The IPC receives a class 2 message from the ECM indicating that the vehicle speed is greater than 10 km/h (6 mph). |
| • | The ignition voltage is between 9.0 volts and 18.0 volts. |
Conditions for Setting the DTC
| • | The IPC does not detect a 4K PPM signal on the vehicle speed signal circuit. |
| • | The condition above must be present for a minimum of 5 seconds. |
Action Taken When the DTC Sets
The IPC stores a DTC B0540 in memory.
Conditions for Clearing the DTC
| • | The history DTC clears after 100 malfunction free warm-up cycles. |
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The IPC receives the clear code command from the scan tool. |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Instrument Cluster Schematics | ||||||||
1 | Did you perform the IPC Diagnostic System Check? | -- | Go to Step 2 | |||||
2 |
Does the voltage measure greater than the specified value? | 9.0 V | Go to Step 3 | Go to Step 4 | ||||
3 | Test the vehicle 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 9 | Go to Step 5 | ||||
4 | Test the vehicle 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 9 | Go to Step 6 | ||||
5 | Inspect for poor connections at the harness connector of the ECM. 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 9 | Go to Step 7 | ||||
6 | Inspect for poor connection at the harness connector of the instrument panel cluster (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 9 | Go to Step 8 | ||||
7 |
Important: Program the replacement ECM. Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data in Engine Controls - 7.8L. Did you complete the replacement? | -- | Go to Step 9 | -- | ||||
8 |
Important: Program the replacement IPC. Replace the IPC. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | ||||
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK | ||||
