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

Circuit Description

The vehicle speed sensor (VSS) is connected to the powertrain control module (PCM). The VSS is mounted on the transmission and monitors the axle drive speed. Based upon the signal that is received from the VSS the PCM supplies a vehicle speed output signal on the VSS output circuit. The cruise control module and the alternative fuels engine control module (ECM) utilize the VSS output circuit.

This DTC is used to indicate no VSS output signal is being monitored by the alternative fuels ECM while engine sensor conditions indicate the vehicle is moving.

Conditions for Running the DTC
    • The engine is operating on alternative fuel.
    • The following DTC's are not set:
      • P0106
      • P0107
      • P0121
      • P0122
      • P0123
    • The MAP sensor signal indicates greater than 57 kPa (17 in Hg).
    • The TP sensor signal indicates throttle angle is open greater than 12 percent.
    • The calculated engine airflow is greater than 40 gms/sec.
    • All conditions have been met for at least 15 seconds.

Conditions for Setting the DTC

The AF ECM monitors vehicle speed of less than 3.2 km/h (2 mph).

Action Taken When the DTC Sets

    • The Alternative Fuels ECM will illuminate the MIL and store the DTC as History during 1 drive trip in which 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 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 the Diagnostic System Check - Alternative Fuels (Engine Controls) .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for a proper vehicle speed output signal. The frequency created by the PCM is equal to about 1 Hz per mile an hour.

    2.

  2. This step tests for a proper vehicle speed output signal at the alternative fuels ECM. The frequency created by the PCM is equal to about 1 Hz per mile an hour.

Step

Action

Values

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 (PCM).
  2. Inspect for stored powertrain DTCs.

Are DTCs DTC P0502 or DTC P0503 stored?

--

Go to Powertrain On Board Diagnostic (OBD) System Check - Automatic Transmission in Transmission/Transaxle in the J Platform Service Manual

Go to Step 3

3
  1. Observe the alternative fuels ECM Freeze Frame and/or 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 and/or 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 any DTCs stored that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Intermittent Conditions

5

  1. Turn the ignition OFF.
  2. Disconnect the cruise control module electrical connector.
  3. Raise and support the vehicle with the drive wheels off the ground.
  4. Connect the J 39200 DMM negative test lead to the VSS input circuit terminal of the cruise control module connector.
  5. Connect the J 39200 DMM positive test lead to battery positive.
  6. Start the engine and place the transmission in Drive.
  7. Measure the DC frequency on the VSS input circuit while rotating the drive wheels at the specified value.

Is the frequency measured greater than the value specified?

32 km/h (20 mph)

15 Hz

Go to Step 6

Go to Step 7

6

  1. Turn the ignition OFF.
  2. Disconnect the alternative fuels ECM.
  3. Connect the J 39200 DMM negative test lead to the VSS input circuit terminal of the ECM connector.
  4. Connect the J 39200 DMM positive test lead to battery positive.
  5. Start the engine and place the transmission in Drive.
  6. Measure the DC frequency on the VSS input circuit while rotating the drive wheels at the specified value.

Is the frequency measured greater than the value specified?

32 km/h (20 mph)

15 Hz

Go to Step 8

Go to Step 11

7
  1. Test the VSS circuit for an open or shorted condition.
  2. Inspect the gasoline control module (PCM) connector terminals for proper contact.
  3. Repair the wiring or terminals as necessary.

Was a repair necessary?

--

Go to Step 12

Go to Step 10

8
  1. Inspect the alternative fuels ECM connector for proper terminal contact.
  2. Repair the terminal as necessary.

Was a repair necessary?

--

Go to Step 12

Go to Step 9

9
  1. Replace the alternative fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .
  2. Program -- flash -- the replacement control module with the correct vehicle software and calibration.

Is the replacement complete?

--

Go to Step 12

--

10
  1. Replace the gasoline control module (PCM). Refer to Powertrain Control Module Replacement .
  2. Program -- flash -- the replacement control module with the correct bi-fuel vehicle software and calibration.

    3. Important: In order to perform the variation learn procedure a switch-over to gasoline operation is necessary. Remove the CNG 20 amp fuse in order to perform the switch-over.

  3. Perform the Crankshaft Position System Variation Learn in Engine Controls-2.2L (LN2) in the J Platform Service Manual.

Is the replacement complete?

--

Go to Step 12

--

11

Repair the open VSS circuit between the alternative fuels ECM and the circuit splice.

Is the repair complete?

--

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs from both control modules.
  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.

Does the DTC run and pass?

--

System OK

Go to Step 2