15 No Vehicle Speed Sensor Signal - (P 0500)

15 NO VEHICLE SPEED SENSOR SIGNAL - (P 0500)





The Vehicle Speed Sensor (VSS), is a Hall-effect sensor mounted on the transmission extension housing. It delivers vehicle speed information to the Powertrain Control Module (PCM) as an input switching voltage between 0 and 5 volts at pin 5 of the PCM's 60-pin connector. When the PCM recognizes 4000 0-to 5-volt switching signals, the PCM assumes the vehicle has traveled one mile. The VSS receives a 9-volt power supply from the PCM on pin 44, and is grounded at pin 51.

ENABLING CONDITIONS
To enable the test of the Vehicle Speed Sensor, the following conditions must be met:

- PCM must not be in the start mode
- Engine temperature must be at least 180°F
- The transmission must be in gear if the vehicle has an automatic transmission
- The engine must have been running for at least 31 seconds
- PCM cannot register that the brake is being applied
- PCM cannot be indicating engine is at idle
- RPM must be 1,792 or higher
- The vacuum indicated by the MAP sensor must be between barometric pressure and ten in. of mercury below barometric pressure

Once the PCM assumes that the vehicle is in motion, information from the VSS is sampled. If the sensor 5 output voltage indicates a speed less than one MPH for 11 seconds. the VSS is then considered to be malfunctioning.

Failure of the VSS is quite noticeable because the speedometer fails to operate. Diagnostic features that depend upon the speed sensor may never execute if the VSS fails, and the speed control will not function (if the vehicle is equipped with speed control). However, since the speedometer is wired independently of the PCM, never assume that the speed sensor has failed just because the speedometer is malfunctioning. Also, never assume that just because the speedometer is working that the PCM is receiving the VSS signal.

The speed sensor is used in the calculation of pulse width (deceleration programs), and is used to aid in the diagnostics of other OBD monitors. Therefore, the MIL is illuminated after the conditions have been met and no VSS pulses are recognized for a total of 11 seconds.

This malfunction could possibly be caused by problems with any of the following components:

- VSS
- 5-volt wire from the VSS to the PCM (open)
- Ground wire from the VSS to the PCM (open)
- Transmission Control Module (TCM)
- PCM
- Pinion gear on the VSS (damaged)