Fault Detection / Management
The ECM performs diagnostic checks on the VSS circuit when the engine is operating at 0 mph. The ECM transmits a voltage signal on the VSS circuit and determines if the return voltage is out of range high or low. When a fault condition is detected, the ECM disables the cruise control and power takeoff. If the road speed limiting option is enabled, the ECM will limit engine rpm for all gears.
The ECM will not set DTCs for VSS circuit failure for vehicles equipped with Allison transmissions.
NOTE: See truck Chassis Electrical Circuit Diagram Manual for circuit numbers, connector and fuse locations. To diagnose Allison transmission VSS sensor problems, see truck Electrical System Troubleshooting Guide and Allison maintenance and diagnostic manuals.
VSS Diagnostic Trouble Codes (DTCs)
DTCs are read using the EST or by counting the flashes from the amber and red ENGINE lamp.
DTC 141
VSS signal out-of-range low
• DTC 141 is set by the ECM when an out of range low condition is detected in the VSS circuit.
• When DTC 141 is active the amber ENGINE lamp is not illuminated.
DTC 142
VSS signal out-of-range high
• DTC 142 is set by the ECM when an out of range high condition is detected in the VSS circuit.
• When DTC 142 is active the amber ENGINE lamp is not illuminated.
DTC 215
VSS signal frequency out-of-range high
• DTC 215 is set by the ECM when the ECM detects a VSS signal greater than 4365 Hz.
Tools
• EST with MasterDiagnostics® software
• EZ-Tech® interface cable
• Electrical System Troubleshooting Guide (truck manual)
• Electrical Circuit Diagrams (truck manual)
