| Free A.S.E. Study Guide An ASE Study Guide for the Automotive Technician |
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| Vehicle Speed Sensors |
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Vehicle Speed Sensors come in several different designs and are used as an
important sesnor input to several vehicle computerized systems. This sensor
inputs data to the transmission for shift control, cruise control for desired
operation, ABS (anti-lock brakes) only to name a few.
Most mount on the transmission or rear axle and send a varying frequency to a
meter and on to the PCM (powertrain control module). In many later model
vehicles you will find them located in the ABS module.
If you don’t see a VSS signal on your scan tool and don’t see it mounted on the
transaxle, it’s probably in the ABS system. This system uses the signal from the
front or all four wheel speed sensors to calculate the vehicle speed.
Transmission/Transaxle mounted speed sensors are driven by a gear located
on the output shaft. This drive gear can be either machined or held in place buy
a clip. Either way it must be inspected for damage as this could be an underlying
cause of premature driven gear wear.
The driven gear is typically made of plastic making it softer than the drive gear. It
is located on the end of the vehicle speed sensor. As the shaft of this sensor
spins it generates an on off signal to the vehicles PCM / TCM. In later model
vehicles this information is shared between computer systems via multiplexing.
Vehicle speed sensors located in the differential use a trigger wheel to generate
the pulse signal required by the related control modules. These VSS systems
use different techniques to achieve the same results.
Diagnosing vehicle speed sensors includes checking the sensor, the wiring,
PCM, and well as comparing symptoms if no code is present. The vehicle code
should in the P 0500 range. The sensor can be tested with a scanner,
multimeter, and specifications.
If a code is not present there are several symptoms leading to this sensor. The
speed sensor affects so many different systems it may not be so difficult to
figure out. For instance, if the vehicle suffered a transmission shifting condition
and a dysfunctional speedometer it may be necessary to check for proper VSS
operation.
important sesnor input to several vehicle computerized systems. This sensor
inputs data to the transmission for shift control, cruise control for desired
operation, ABS (anti-lock brakes) only to name a few.
Most mount on the transmission or rear axle and send a varying frequency to a
meter and on to the PCM (powertrain control module). In many later model
vehicles you will find them located in the ABS module.
If you don’t see a VSS signal on your scan tool and don’t see it mounted on the
transaxle, it’s probably in the ABS system. This system uses the signal from the
front or all four wheel speed sensors to calculate the vehicle speed.
Transmission/Transaxle mounted speed sensors are driven by a gear located
on the output shaft. This drive gear can be either machined or held in place buy
a clip. Either way it must be inspected for damage as this could be an underlying
cause of premature driven gear wear.
The driven gear is typically made of plastic making it softer than the drive gear. It
is located on the end of the vehicle speed sensor. As the shaft of this sensor
spins it generates an on off signal to the vehicles PCM / TCM. In later model
vehicles this information is shared between computer systems via multiplexing.
Vehicle speed sensors located in the differential use a trigger wheel to generate
the pulse signal required by the related control modules. These VSS systems
use different techniques to achieve the same results.
Diagnosing vehicle speed sensors includes checking the sensor, the wiring,
PCM, and well as comparing symptoms if no code is present. The vehicle code
should in the P 0500 range. The sensor can be tested with a scanner,
multimeter, and specifications.
If a code is not present there are several symptoms leading to this sensor. The
speed sensor affects so many different systems it may not be so difficult to
figure out. For instance, if the vehicle suffered a transmission shifting condition
and a dysfunctional speedometer it may be necessary to check for proper VSS
operation.