GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Optra 🢒 Engine 🢒 Engine Controls and Fuel - 2.0L (L34 GMDAT) 🢒 DTC P0502

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0502: Vehicle Speed Sensor (VSS) Circuit

Circuit/System Description

The vehicle speed information is provided to the engine control module (ECM) by the vehicle speed sensor (VSS). The VSS is a permanent magnet generator that is mounted to the transmission and produces a pulsing voltage. The AC voltage amplitude and frequency increases with vehicle speed. The ECM converts the pulsing voltage into km/h (mph). The ECM supplies the VSS signal to the following components:

    • The instrument panel for speedometer and odometer operation
    • The cruise control module
    • The multi-function alarm module

Conditions for Running the DTC
    • DTCs P0106, P0107, P0108, P0115, P0117, P0118, P0122, P0123, P0125, P0128, P0217, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0300, P0351, P0352, P0402, P0404, P0405, P0406, and P042E are not set.
    • The engine is running.
    • The engine coolant temperature (ECT) is greater than 60°C (140°F).
    • The ignition 1 voltage is between 11-16 volts.
    • DTC P0502 runs continuously once the above conditions are met.
    • The following are additional Conditions for Running for the applicable test:

Power Test

       - The engine speed is between 1,200-4,000 RPM.
       - The throttle position (TP) sensor is between 25-60 percent.
       - The manifold absolute pressure (MAP) is greater than 60 kPa.

Deceleration Test

       - The MAP is less than 30 kPa.
       - The change in engine speed per cycle is less than or equal to 50 RPM/cycle.
       - The throttle position (TP) sensor is less than or equal to 0.8 percent.
       - The engine speed is between 1,800-6,000 RPM.

Conditions for Setting the DTC

The ECM detects that the vehicle speed is less than 5 km/h (3.1 mph) for greater than 35 seconds.

Action Taken When the DTC Sets
    • DTC P0502 is a Type B DTC.
    • The cruise system will be disabled.
    • The cooling fans will be commanded ON at low speed.

Conditions for Clearing the DTC

DTC P0502 is a Type B DTC.

Diagnostic Aids
    • Ensure the VSS is correctly torqued to the transmission housing.
    • This DTC may be set due to an instrument panel (IP) cluster condition.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Raise the drive wheels.

    2. Notice: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel.

  2. Support the lower control arms so that the drive axles are in a horizontal position.
  3. Engine idling, place the transmission into 2nd gear.
  4. Observe the scan tool VSS parameter. The following should display a vehicle speed once the drive wheels are at a speed above 8 km/h (5 mph):
    5. • The VSS parameter
    • The speedometer
  5. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the VSS.
  2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal A and ground.
    3. ⇒If greater than the specified range, repair the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the ignition 1 voltage circuit terminal C and ground.
    4. ⇒If the test lamp does not illuminate, test the ignition 1 voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition 1 voltage circuit fuse is open, test all components connected to the ignition 1 voltage circuit and replace as necessary.
  4. Ignition ON, test for 9-11 volts between the signal circuit terminal B and ground.
    5. ⇒If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
    ⇒If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  5. If the voltage is within the specified range, test or replace the VSS.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine control module replacement, setup, and programming