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 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 the DTC information into memory when the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM displays this failure information in the Failure Records. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
Conditions for Clearing the DTC
| • | 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. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | use a scan tool in order to clear the DTC. |
Diagnostic Aids
For intermittent diagnosis, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics in Engine Controls - 3.4L Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views in Engine Controls - 3.4L | ||||
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 P0717 or P0722 current in the transmission control module (TCM)? | -- | Go to DTC P0717 or DTC P0722 in Automatic Transaxle - AF33-5 | 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 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 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 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 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 |
