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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 Sierra Denali 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC P0502 or P0503

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 Low Voltage

DTC P0503: Vehicle Speed Sensor (VSS) Circuit Intermittent

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

VSS Low Signal

--

P0502, P0503

--

--

VSS High Signal

P0502, P0503

P0502, P0503

P0502, P0503

--

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

Conditions for Running the DTC

P0502

    • DTC P0120, P0220 or P0503 are not set.
    • The TP sensor angle is more than 3.5 percent.
    • The engine is running.
    • The system voltage is 8-18V.
    • TFT is more than -40°C (-40°F)
    • The engine speed is 1,500-6,500 RPM.
    • Vehicle speed is less than 200 km/h (124 mph).
    • Engine torque is 68-8192 N·m (50-6,042 lb ft).
    • The PTO is not active.

P0503

    • The system voltage is 8-18V.
    • The engine speed is 500-7,500 RPM.
    • Transmission out speed change is less than 146 RPM for 2 seconds.
    • The PTO is not active.
    • The OSS is at least 292 RPM for 2 seconds.
    • The OSS has not changed more than 146 RPM for 2 seconds.
    • The 4WD range has not changed within 6 seconds.

Conditions for Setting the DTC

P0502

The transmission output speed is 58 RPM or less for 5 seconds.

P0503

The transmission output speed drops 351 RPMs in less than 3 seconds.

Action Taken When the DTC Sets

P0502 and P0503 are Type B DTCs.

Conditions for Clearing the DTC

P0502 and P0503 are Type B DTCs.

Reference Information

Schematic Reference

Manual Transmission Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual Transmission Description and Operation

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

Special Tools

J 35616 GM-Approved Terminal Test Kit

Circuit/System Verification
  1. Raise and support the drive wheels.
  2. Start and idle the engine.
  3. Place the transmission in second gear and release the clutch pedal.
  4. Monitor VSS parameter on the scan tool. The VSS parameter should increase as the drive wheel speed increases.
  5. Operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

Circuit/System Testing
  1. Disconnect the ECM harness connector X1.
  2. Measure for 1,300-1,500 ohms at 25°C (77°F) between the VSS high signal circuit terminal 71 and the VSS low signal circuit terminal 72.
    3. ⇒If the value is greater than 1,500 ohms test the VSS high signal circuit and the VSS low signal circuit for an open/high resistance. If the circuits/connections test normal, replace the vehicle speed sensor.
    ⇒If the value is less than 1,300 ohms test the VSS high signal and the VSS low signal circuits for a shorted together condition. If the circuits/connections test normal, replace the vehicle speed sensor.
  3. Measure for more than 10 ohms of resistance between the VSS high signal circuit terminal 71 and ground.
    4. ⇒If the value is less than the specified range, repair the short to ground.
  4. Measure for more than 10 ohms of resistance between the VSS low signal circuit terminal 72 and ground.
    5. ⇒If the value is less than the specified range, repair the short to ground.
  5. Reconnect the ECM connector. Disconnect the VSS connector.
  6. Ignition ON, test the VSS high signal circuit terminal B for a short to voltage.
    7. ⇒If all circuits/connections test normal, test or replace the VSS.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  Vehicle Speed Sensor Replacement
    •  Control Module References for ECM replacement, setup and programming.