GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Savana (CNG) 🢒 DTC 🢒 DTC P0500

Circuit Description

The vehicle speed output signal is generated by the gasoline Control Module (VCM/PCM or ECM). The signal is a duplicate of the vehicle speed sensor (VSS) signal that the gasoline Control Module receives from the VSS. The gasoline Control Module (VCM/PCM or ECM) contains an integrated circuit called a driver that switches the signal circuit to ground at a rate of 4,000 pulses for every km/h (mph) the vehicle is driven. Various modules -- IP, Cruise, Alternative Fuels ECM, etc. -- that are connected to the vehicle speed output circuit convert the 4K PPM into a vehicle speed value.

This DTC is used to indicate that 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.

Diagnostic Aids

Intermittent Condition

A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermittent Conditions diagnostic information located in Symptoms - Engine Controls. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Engine Controls) .

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Alternative Fuels Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2
  1. Using the scan tool, establish communication with the gasoline Control Module (VCM/PCM or ECM).
  2. Inspect for DTC P0608.

Is DTC P0608 stored as History?

Go to DTC P0608 in the Instrument Panel, Gages, and Console section of the G Van Service Manual

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 5

Go to Step 4

4

The fault is not present. Refer to Diagnostic Aids.

Are there any DTCs stored that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

Go to Intermittent Conditions

5
  1. Test the vehicle speed output circuit for an open condition between the circuit splice and the Alternative Fuels ECM connector.
  2. Inspect the Alternative Fuels ECM connector for poor terminal contact.
  3. Repair circuit or terminal contact as necessary.

Was a circuit or terminal repair made?

Go to Step 7

Go to Step 6

6
  1. Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .
  2. Program the replacement Control Module with the correct vehicle software and calibration.

Is the replacement complete?

Go to Step 7

--

7
  1. Reconnect all disconnect or removed components, connectors, fuses, etc.
  2. Using a scan tool, clear all DTC Information from BOTH the gasoline Control Module (VCM/PCM or ECM) and the Alternative Fuels ECM.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. Operate the vehicle within the Conditions for Running the DTC until the scan tool indicates the diagnostic ran.

Does the scan tool indicate the DTC passed?

 

Go to Step 2