Vehicle Speed Sensor (VSS) (Peugeot Eurovans 806)

Vehicle Speed Sensor (VSS) (see illustration 11.28) used to notify the electronic control unit of the vehicle's speed. This sensor is a Hall sensor and is located directly on the gearbox. Voltage is supplied to the vehicle speed sensor from the energized relay. When the speedometer drive cable rotates, the Hall sensor alternately turns on and off to send a square wave signal to the electronic control unit. Signal frequency (8 pulses per revolution) determines the speed of the car.

Vehicle Speed Sensor (VSS) Voltage Values

Terminal numbers

See illustration 11.29

Vehicle Speed Sensor (VSS) Frequency

8 pulses per revolution of the speedometer drive cable.

Checking the vehicle speed sensor (VSS) (general check)

1. Inspect the vehicle speed sensor multi-pin connector for signs of corrosion or damage.

2. Make sure the connector terminal pins are properly installed and have good contact with the vehicle speed sensor connector.

Checking the functionality of the vehicle speed sensor (VSS)

1. The test is quite simple. The sensor has three wires: a power wire, a ground wire, and a signal wire.

2. Connect the positive lead of the voltmeter to the vehicle speed sensor multi-pin connector (see note 2) or connect the output block (OB) between the ECU multi-pin connector and the ECU.

3. Connect the negative probe of an oscilloscope, breaker duration meter, or voltmeter to ground on the engine.

4. Connect the positive probe of an oscilloscope, contact duration meter, or voltmeter to terminal #3 of the vehicle speed sensor signal wire (see illustration 11.30).

Checking the signal from the vehicle speed sensor (VSS)

Note: The supply voltage can be generated from the ignition switch or a relay. If the voltage is supplied from a relay, the connection can be from the first or second contact of the relay. The first relay contact supplies voltage when the ignition is on, the second relay contact supplies voltage only when the engine is running.

1. Turn on the ignition or start the engine.

2. The signal is sent by the sensor when the drive wheels rotate. Wheel rotation can be achieved in one of two ways:

• Push the car forward.
• Place the vehicle on an inclined plane so that the drive wheels can rotate freely. Either spin the wheels manually or start the engine at low speed.

3. The device should display the waveform, duty cycle or voltage.

No signal or signal is unstable, duty cycle or voltage

1. The vehicle speed sensor multi-pin connector is disconnected, ignition is on.

2. Check the voltage supply to the vehicle speed sensor power wire terminal.

3. No voltage: Check the voltage supply from the ignition switch or relay, depending on the system design.

4. Check the ground at the vehicle speed sensor ground wire terminal.

5. Disconnect the vehicle speed sensor multi-pin connector.

6. Connect the positive probe of the voltmeter to the signal wire terminal.

7. The device should indicate voltage between 8.5 and 10.0 Volts.

The voltage in the grounding and power supply wires is within normal limits

• The vehicle speed sensor may be faulty or not turning the speedometer drive (i.e. the cable is broken or there is a malfunction in the gearbox).

There is no signal voltage

1. Check the voltage at the multi-pin connector terminal of the electronic control unit.

2. If the voltage of the electronic control unit is within the normal range, check the signal wire for continuity.

3. If there is no voltage at the contact of the electronic control unit, then check the power and ground contacts of the unit. If the contacts are in working order, then the electronic control unit may be faulty.

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