Circuit Description
The vehicle speed signal circuit is an input to the throttle actuator control (TAC) module from the powertrain control module (PCM). The PCM provides a constant voltage signal on the vehicle speed signal circuit. The PCM creates the vehicle speed signal by internally pulsing the vehicle speed signal to ground. The TAC module uses the vehicle speed signal from the PCM, in order to determine the vehicle speed. The TAC module then sends a universal asynchronous receiver transmitter (UART) serial data message to the PCM indicating the vehicle speed that the TAC module has detected.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0608 Vehicle Speed Output Circuit
Conditions for Running the DTC
| • | The vehicle is in Drive or Reverse. |
| • | The vehicle speed is greater than 8 km/h (5 mph). |
| • | There are no VSS DTCs present in the PCM. |
| • | The ignition voltage is between 9-16 volts. |
Conditions for Setting the DTC
| • | The PCM sends a 8 km/h (5 mph) signal on the vehicle speed signal circuit to the TAC module. The TAC module sends a UART serial data message to the PCM indicating that the vehicle speed is 0 km/h (0 mph). |
| • | The condition must be present for greater than 4 seconds. |
Action Taken When the DTC Sets
| • | The cruise control system is disabled. |
| • | The PCM stores a DTC P0608 in memory. |
| • | The PCM records the operating conditions at the time the DTC sets. The PCM 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 PCM receives the clear code command from the scan tool. |
Diagnostic Aids
| • | If any additional powertrain DTCs are stored, refer to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information. |
| • | For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Cruise Control Schematics Connector End View Reference: Powertrain Control Module Connector End Views in Engine Controls - 3.5L (LX9) | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the Vehicle Speed Sensor parameter indicate any vehicle speed? | -- | Go to Step 4 | Go to Step 3 |
3 | Is DTC P0502 or P0503 current in the PCM? | -- | Go to Diagnostic Aids | Go to Step 7 |
4 |
Does the voltage measure greater than the specified value? | 8.5 V | Go to Step 5 | Go to Step 6 |
5 | 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 11 | Go to Step 8 |
6 | 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 11 | Go to Step 7 |
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 11 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the TAC module. 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 11 | Go to Step 10 |
9 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the TAC module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
