Circuit Description
The engine control module (ECM) creates the engine speed output signal by pulsing the circuit to ground at a predetermined hertz rate. The ECM pulses the circuit at the same rate as the engine speed signal input. The ECM monitors the voltage on the engine speed output circuit. If the ECM determines the voltage is out of the normal operating range, a DTC sets. The IPC converts the 2 pulses per engine revolution signal to a tachometer position. The engine speed is sent to the IPC over a discreet wire from the ECM. The tachometer signal is pulled up to B+ in the IPC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0654 Engine Speed Output Circuit
Conditions for Running the DTC
| • | The engine speed is greater than 400 RPM. |
| • | The ignition voltage is greater than 9 volts and less than 18 volts. |
Conditions for Setting the DTC
| • | The ECM detects that the commanded state of the driver and the actual state of the control circuit do not match. |
| • | All conditions are present for a minimum of 5 seconds. |
Action Taken When the DTC Sets
| • | The ECM stores the DTC information into memory when the diagnostic runs and fails. |
| • | The ECM records the operating conditions at the time the diagnostic fails. The ECM displays the failure information in the Failure Records on the scan tool. |
Conditions for Clearing the DTC
| • | The history DTC clears after 40 malfunction-free warm-up cycles. |
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The ECM receives the clear code command from the scan tool. |
Diagnostic Aids
Important: Remove any debris from the ECM connector surfaces before servicing the ECM. Inspect the ECM connector gaskets when diagnosing/replacing the ECM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the ECM.
Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature, etc.) that you observed. This will isolate when the DTC failed.
For an intermittent, refer to Testing for Intermittent Conditions and Poor Connections .
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Instrument Cluster Schematics Connector End View Reference: Master Electrical Component List | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the tachometer indicate engine RPM? | -- | Go Diagnostic Aids | Go to Step 3 |
3 |
Does the voltage measure greater than the specified value? | 9.5 V | Go to Step 4 | Go to Step 6 |
4 | Test the engine speed signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 5 |
5 | Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and repair the condition? | -- | Go to Step 8 | Go to Step 7 |
6 | Repair the short to ground in the vehicle speed signal circuit. Refer to Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | -- |
7 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 8 | -- |
8 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
