Circuit Description
The vehicle speed output signal is generated by the powertrain control module (PCM). The signal is a duplicate of the vehicle speed sensor (VSS) signal that the PCM receives from the VSS. The PCM contains an integrated circuit called a driver that switches the signal circuit to ground at a rate of 4,000 pulses for every 1.6 km/h (1 mph) the vehicle is driven. Various modules that are connected to the vehicle speed output circuit convert the 4K PPM into a vehicle speed value.
This DTC sets when the Alternative Fuels ECM cannot monitor an accurate vehicle speed.
Conditions for Running the DTC
The engine is operating on Alternative Fuel.
Conditions for Setting the DTC
The Alternative Fuels ECM monitors a vehicle speed output signal circuit fault.
Action Taken When the DTC Sets
| • | A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History. |
| • | The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails. |
| • | The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | The Last Test Failed status will clear when the DTC runs and passes. |
| • | The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes. |
| • | The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC. |
| • | All DTC Information can be cleared with a scan tool. |
Step | Action | Yes | No | ||||
|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||||||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) | ||||
2 |
Is DTC P0608 stored as History? | Go to DTC P0608 in Instrument Panel, Gages, and Console in the C/K Pickup Service Manual | Go to Step 3 | ||||
3 |
Does the DTC fail this ignition cycle? | Go to Step 4 | Go to Intermittent Conditions | ||||
4 | Test the vehicle speed output circuit for an open condition between the circuit splice and the Alternative Fuels ECM connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you find and correct the condition? | Go to Step 7 | Go to Step 5 | ||||
5 | Inspect for poor terminal contact at the harness connector of the Alternative Fuels ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual. Did you find and correct the condition? | Go to Step 7 | Go to Step 6 | ||||
6 | Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement . Did you complete the replacement? | Go to Step 7 | -- | ||||
7 |
Does the DTC run and pass? | Go to Step 8 | Go to Step 2 | ||||
8 | With a scan tool, select Capture Info in order to observe the stored information. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |||||
