No Vehicle Speed Sensor Signal

NAME OF CODE
No Vehicle Speed Sensor Signal

WHEN MONITORED
With engine running more than 31 seconds, engine temperature greater than 120°F, transmission not in PARK or NEUTRAL, brakes not applied, engine RPM greater than 1800, and Manifold Absolute Pressure (MAP) vacuum less than 11".

SET CONDITION
No signal from the vehicle speed sensor for more than 11 seconds.

THEORY OF OPERATION
The vehicle speed sensor (VSS) is a hall-effect type sensor used to detect vehicle speed. The Powertrain Control Module (PCM) calculates the vehicle speed based on the VSS signal. The PCM supplies 8 volts from cavity 7 to power up the sensor. Sensor ground is supplied by PCM cavity 4. The PCM also supplies a 5.0 volt pull up voltage to the sensor from cavity 47. The VSS signal is created when the sensor alternates the 5.0 volt pull up from high to low.

POSSIBLE CAUSES
- Open or shorted signal circuit
- Speedometer pinion damaged
- Open 8-volt supply circuit
- Open sensor ground circuit
- Failed vehicle speed sensor
- Failed PCM