Circuit Description
Various components apply a voltage to the vehicle speed output circuit. The powertrain control module (PCM) creates the vehicle speed output signal by rapidly grounding this circuit via an internal switch called a driver. The various components recognize the voltage being pulled to ground as an indication of vehicle speed.
The driver supplies the ground for the component being controlled. Each driver has a fault line which the PCM monitors. When the PCM commands a component ON, the voltage of the control circuit should be low, near 0 volts. When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the fault line status changes causing the DTC to set. This DTC sets when the VSS output circuit is grounded or shorted to a voltage.
Conditions for Running the DTC
| • | The engine speed is more than 400 RPM. |
| • | The ignition voltage is between 6-18 volts. |
Conditions for Setting the DTC
| • | The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match. |
| • | The condition must be present for a minimum of 5 seconds. |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
Using Freeze Frame and Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and 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 or a fail. Operate the vehicle within the same Freeze Frame conditions, such as RPM, load, vehicle speed, temperature etc., that you observed. This will isolate when the DTC failed.
For an intermittent, refer to Symptoms .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies if the fault is present.
-
This step tests for the proper signal voltage.
-
This step tests for an open circuit between the instrument panel cluster (IPC) and connector C100.
-
This step tests for a grounded circuit between the IPC and connector C100.
-
This step tests for an open circuit between the PCM and connector C100.
-
This step tests for a grounded circuit between the PCM and connector C100.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Important: If the instrument panel (IP) is completely inoperative, refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console. Caution: To avoid any vehicle damage, serious personal injury or death when major components are removed from the vehicle and the vehicle is supported by a hoist, support the vehicle with jack stands at the opposite end from which the components are being removed and strap the vehicle to the hoist. Does the vehicle speedometer indicate a vehicle speed? | -- | Go Diagnostic Aids | ||
Does the DMM display a voltage more than the specified value? | 9.5 V | |||
Does the DMM display continuity? | -- | |||
Test continuity from the vehicle speed output (4K) circuit to battery ground. Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity? | -- | Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console | ||
Does the DMM display continuity. | -- | |||
Test the continuity of the vehicle speed output (4K) circuit from the PCM harness connector to ground using the DMM . Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity? | -- | |||
8 | Repair the open vehicle speed output (4K) circuit from the IPC to connector C100. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
9 | Repair the grounded vehicle speed output (4K) circuit from the IPC to connector C100. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
10 | Repair the open vehicle speed output (4K) circuit from the PCM to C100. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
11 | Repair the grounded vehicle speed output (4K) circuit from the PCM to C100. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
12 |
Did you find and repair the condition? | -- | ||
13 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
14 |
Does the scan tool indicate that this test passed? | -- | ||
15 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
