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 Descriptors
DTC P0502: Vehicle Speed Sensor (VSS) Circuit Low VoltageDTC 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, P0121 or P0503 is not set. |
| • | The TP sensor angle is more than 12 percent. |
| • | The engine speed is 1,000-6,800 RPM for 8 seconds. |
| • | The system voltage is 10-18V. |
| • | Engine torque is 40-300 N·m (30-221 lb ft). |
P0503
| • | DTC P0502 is not set. |
| • | The engine speed is 450-6,800 RPM for 8 seconds. |
| • | The system voltage is 10-18V. |
| • | The time since the last gear change is 6 seconds or more. |
| • | The engine speed change is more than 500 RPM in 2 seconds. |
Conditions for Setting the DTC
P0502
The transmission output speed is 100 RPM or less for 3 seconds.
P0503
The transmission output speed drops 1,500 RPM in less than 0.5 seconds.
Action Taken When the DTC Sets
| • | P0502 and P0503 are Type B DTCs. |
| • | Cruise control is disabled. |
Conditions for Clearing the DTC
P0502 and P0503 are Type B DTCs.
Reference Information
Schematic Reference
Manual Transmission Schematics
Connector End View Reference
Description and Operation
Transmission System Description and Operation
Electrical Information Reference
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information.
Special Tools
J 35616 GM-Approved Terminal Test Kit
Circuit/System Verification
- Raise and support the drive wheels.
- Support the lower control arms so that the drive axles are in a horizontal position.
- Start and idle the engine.
- Place the transmission in second gear and release the clutch pedal.
- Monitor VSS parameter on the scan tool. The VSS parameter should increase as the drive wheel speed increases.
- 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.
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.
Circuit/System Testing
- Disconnect the ECM harness connector X1.
- Measure for 1,300-1,500 ohms at 25°C (77°F) between the VSS high signal circuit terminal 54 and the VSS low signal circuit terminal 34.
- Measure for more than 10 ohms of resistance between the VSS high signal circuit terminal 54 and ground.
- Measure for more than 10 ohms of resistance between the VSS low signal circuit terminal 34 and ground.
- Reconnect the ECM connector. Disconnect the VSS connector.
- Ignition ON, test the VSS high signal circuit terminal B for a short to voltage.
| ⇒ | 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. |
| ⇒ | If the value is less than the specified range, repair the short to ground. |
| ⇒ | If the value is less than the specified range, repair the short to ground. |
| ⇒ | If all circuits/connections test normal, test or replace the VSS. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for ECM replacement, setup and programming |
