Vehicle Speed Sensor
M/T - Vehicle speed information is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor (VSS). The VSS is a permanent magnet generator that is mounted on the transaxle and produces a pulsing voltage whenever vehicle speed is over 3 MPH. See Fig 1 . The AC voltage amplitude and frequency increases with vehicle speed. The PCM converts the pulsing voltage into MPH (km/h). The PCM supplies the necessary signal to the instrument panel for speedometer, odometer operation and to the cruise control and multi-function alarm module.
A/T Input Shaft Speed Sensor - The Automatic Transmission Input Shaft Speed Sensor (AT ISS) is a magnetic inductive pickup that relays information about the transmission input speed to the PCM. See Fig 2 . The PCM uses this information to control the line pressure, TCC apply and release, and the transmission shift patterns. This information is also used to calculate the appropriate operating gear ratios and TCC slippage. On Impala, the AT ISS mounts on the transmission cover, next to the automatic transmission input shaft speed sensor reluctor wheel assembly. An air gap of 0.0032-0.0834" (0.08-2.12 mm) occurs between the sensor and the teeth on the speed sensor reluctor wheel as the drive sprocket rotates. The speed sensor reluctor wheel is secured to and turns with the drive sprocket by the tangs on the drive sprocket forward thrust washer. On Alero and Monte Carlo, the AT ISS mounts on the transmission case under the channel plate next to the drive sprocket. An air gap of 0.010-0.114" (0.26-2.90 mm) is maintained between the sensor and the teeth of the drive sprocket.
The sensor consists of a permanent magnet surrounded by a coil of wire. As the turbine shaft rotates the speed sensor reluctor wheel and the drive sprocket, an AC signal is produced by the AT ISS sensor. This AC signal consists of a voltage and frequency that changes based on vehicle speed. The PCM uses the frequency portion of this signal to determine input shaft speed. Higher input shaft speeds induce a higher frequency and a higher voltage measurement at the sensor. The voltage portion of the signal is used in diagnostic procedures.
Sensor resistance should measure between 820-1020 ohms at 68°F (20°C). Output voltage will vary with the vehicle speed from a minimum of 0.5 volt AC at 300 RPM to 200 volts at 6000 RPM.
A/T Output Shaft Speed Sensor - The Automatic Transmission Output (Shaft) Speed Sensor (A/T OSS) is a magnetic inductive pickup that relays vehicle speed information to the PCM. See Fig 3 . The PCM uses this information to control shift timing, line pressure, and TCC apply and release.
The VSS mounts in the case extension at the vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. An air gap of 0.011-0.062" (0.27-1.57 mm) occurs between the sensor and the teeth on the vehicle speed sensor reluctor wheel as the final drive carrier assembly rotates.
The sensor consists of a permanent magnet surrounded by a coil of wire. As the vehicle speed sensor reluctor wheel on the final drive carrier assembly rotates, an AC signal is produced by the VSS. This AC signal consists of a voltage and frequency that changes based on vehicle speed. The PCM uses the frequency portion of this signal to determine vehicle speed. Higher vehicle speeds induce a higher frequency and a higher voltage measurement at the sensor. The voltage portion of the signal is used in diagnostic procedures.
On Impala, sensor resistance should measure between 1650-2200 ohms at 68°F (20°C). Output voltage will vary with vehicle speed from a minimum of 0.5 volt AC at 100 RPM to 200 volts at 6000 RPM.
On Alero and Monte Carlo, sensor resistance should be 1500-1650 ohms when measured at 68°F (20°C). Output voltage will vary with speed from a minimum of 0.5 volt AC at 25 RPM to 200 volts AC at 1728 RPM.