For 1990-2009 cars

### 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 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).

#### P0503

• | The system voltage is 8-18V.

• | 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

#### 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

Engine Control Module Scan Tool Information

#### Special Tools

J 35616 GM-Approved Terminal Test Kit

### Circuit/System Verification

1. Raise and support the drive wheels.

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. 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. 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.

⇒ | 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 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 ohms 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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• | Vehicle Speed Sensor Replacement

• | Engine Control Module Replacement or Engine Control Module Replacement

• | Engine Control Module Programming and Setup