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 provide 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, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0300, P0351, P0352, P0402, P0404, P0405, P0406, and P042E are not set.

• | The engine is running.

• | The engine coolant temperature (ECT) is more 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 more 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 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 more than 35 seconds.

### Action Taken When the DTC Sets

DTC P0502 is a Type A DTC

### Conditions for Clearing the DTC

DTC P0502 is a Type A DTC

### Diagnostic Aids

• | Ensure the VSS is correctly torqued to the transmission housing.

• | This DTC may be set due to an instrument panel (I/P) cluster condition.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

1. Raise 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. Engage the transmission into 2nd gear.
5. Observe the VSS parameter with a scan tool. The following should display a vehicle speed once the drive wheels are at a speed above 8 km/h (5 mph):

• | The VSS parameter

• | The speedometer

6. If the vehicle passes the Circuit/System Verification Test, then 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 Data List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the VSS.

Important: The test lamp is used to load the circuit and may not illuminate.

2. Connect a test lamp between the ignition voltage circuit and ground circuit of the VSS.
3. Ignition ON, test for battery voltage between the ignition voltage circuit and ground.

⇒ | If less than battery voltage, repair the ignition voltage circuit for a short to ground, or an open/high resistance.

4. Ignition ON, test for less than 0.1 volt between the VSS ground circuit and ground.

⇒ | If greater than 0.1 volt repair the ground circuit for an open/high resistance.

5. Ignition ON, test for 9-11 volts between the signal circuit of the VSS and ground.

⇒ | If less than 9 volts test the VSS signal circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the ECM.

⇒ | If greater than 11 volts test the VSS signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.

6. If the voltage is within the specified range replace the VSS.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Instrument Cluster Replacement

• | Control Module References for ECM replacement, setup, and programming