Q: How to replace the ISS or OSS sensors on automatic transmissions on Chevrolet Express?
A: ISS and OSS sensors are located on the Jeff side of 4LB0-E and 4L85-E automatic transmissions; the ISS sensor near the front of the transmission and the OSS near the rear. ISS and OSS sensors are not used on 4L60-E and 4L65-E automatics, which are equipped instead with a single Vehicle Speed Sensor (VSS). Disconnect the cable from the negative battery terminal. Raise the vehicle and support it securely on jackstands. The ISS and OSS sensors are identical in appearance (and are replaced exactly the same way), so make sure that you've correctly identified the sensor that you wish to replace. Disconnect the electrical connector from the ISS or OSS sensor. To remove an ISS or OSS sensor, disconnect the electrical connector and remove the sensor mounting bolt. Place a drain pan underneath the sensor that you're going to replace. Remove the sensor mounting bolt and pull out the sensor. Installation is the reverse of removal. When you're done, check the transmission fluid level and add fluid as necessary.
Q: What is the location and removal process for the VSS on Chevrolet Express?
A: The 4L60-E and 4L65-E transmissions have their VSS located on the right side of the extension housing. However, both of the 4L80-E and 4L85-E transmissions do not use VSS, instead, they have Input Shaft Speed (ISS) and Output Shaft Speed (OSS) sensors. Disconnecting the cable at its negative battery terminal is important. To prevent rolling and slipping off, put the vehicle on jack stands after lifting it. In case of oil spills while working with the vehicle speed sensor, keep a drain pan beneath it. The electrical connector should be detached from the Vehicle Speed Sensor. For removal of VSS remove the electrical connector as well as sensor mounting bolt. After that remove VSS mounting bolt and extract VSS from transmission. If you want to remove a VSS in this situation, you can grab it tightly then move it back and forth while removing it out of transmission. In case VSS has O-ring, ensure that you check whether it is torn or worn out so that you can replace it if need be. Replace if damaged. When installing a new VSS replace the O-ring even if old one looks fine here. Reinstallation is simply done by reversing what was done during removal process for installation purposes. Therefore, fill up transmission fluid up to required level after inspection process is over.