SMU - Speedometer Control Unit Configuration/Replacement

This bulletin is being issued to update the service and configuration information for the speed sensor control module on pages 8-77 through 8-79 of the 2000 Isuzu Commercial Truck, Forward, Tiltmaster Service Manual supplement.

When replacing or servicing the speed sensor control module, the following procedure must be completed to insure speedometer accuracy.

When servicing a speed sensor control module for an inaccuracy condition, the module should be reconfigured based on the vehicle configuration. The module should not need replacement. However, replacement of the module may be required if no speedometer output is found and Service Manual diagnostics lead to a replacement.

When servicing a vehicle for improper speedometer display, perform the following steps:

1. Locate the speed sensor control module (GM P/N 97725738 or Isuzu P/N 1-80190-021-1). This module is mounted beneath the dash panel, just above and in front of the ALDL connector. The module is black with a wiring harness stuck into the front of the module.
2. Using a 6 mm (¼ in) drill bit, with a drill stop placed 6 mm (¼ in) from the tip, carefully drill a hole in the speed sensor control module closeout cover (GM P/N 97726176 or Isuzu P/N 1-80199-001-0). This cover is located just to the side of the wiring harness connector and is approximately 25 mm (1 in) wide and 13 mm (½ in) high.
3. Carefully place a small pry bar into the drilled hole and snap the cover cap from the module.
4. Set the calibration switches within the speed sensor control module using the following information in the table. Transmission Type (manual or automatic) and Differential Gear Ratio information are required prior to setting the speed sensor control module switches. Set the switches to match the correct values in the table.
5. Snap a new cover in place.