P0503
DTC P0502 or P0503
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.
DTC Descriptors
DTC P0502
- Vehicle Speed Sensor (VSS) Circuit Low Voltage
DTC P0503
- Vehicle Speed Sensor (VSS) Circuit Intermittent
Diagnostic Fault Information
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 8-18 V.
* 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 Nm (50-6,042 lb ft).
P0503
* The system voltage is 8-18 V.
* The engine speed is 500-7,500 RPM.
* Transmission output speed change is less than 146 RPM for 2 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 (Tremec 6-Speed - Manual Transmission)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Manual Transmission Description and Operation (Manual Transmission Description and Operation)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Engine Control Module Scan Tool Information (LS3, L99) (Scan Tool Testing and Procedures)Engine Control Module Scan Tool Information (LLT) (Scan Tool Testing and Procedures)
Special Tools
J 35616 - GM-Approved Terminal Test Kit
For equivalent regional tools, refer to Special Tools (Special Tools and Equipment).
Circuit/System Verification
1. Raise and support the drive wheels.
Caution: 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. Start and idle the engine.
4. Place the transmission in second gear and release the clutch pedal.
5. Monitor VSS parameter on the scan tool. The VSS parameter should increase as the drive wheel speed increases.
6. After performing the above steps, verify that the DTC does not reset by operating the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions you observe from the Freeze Frame/Failure Records data. If the vehicle passes the Circuit/System Verification procedure, then STOP. Do not perform the Circuit/System Testing or Component Testing as this may result in an unnecessary part replacement. Refer to Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections).
Circuit/System Testing
Note: You must perform the Circuit/System Verification first.
1. Disconnect the ECM harness connector X1.
2. Measure for 1,300-1,500 ohm at 25°C (77°F) between the VSS high signal circuit terminal 71 and the VSS low signal circuit terminal 72.
• If the value is greater than 1,500 ohm 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 ohm 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 ohm between the VSS high signal circuit terminal 71 and ground.
• If the value is less than the specified range, repair the short to ground.
4. Measure for more than 10 ohm between the VSS low signal circuit terminal 72 and ground.
• 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.
• If all circuits/connections test normal, test or replace the VSS.
7. If all circuits test normal, replace the ECM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Vehicle Speed Sensor Replacement (Tremec 6-Speed - Manual Transmission)
* Engine Control Module Replacement (Service and Repair)
* Engine Control Module Programming and Setup (LS3, L99) (Testing and Inspection)Engine Control Module Programming and Setup (LLT) (Testing and Inspection)