Vehicle Speed Sensor: Description and Operation

The Vehicle Speed Sensor (VSS) -G68- sends a speed signal to the speedometer and from there the signal goes on to the Engine Control Module (ECM). This speed signal initiates the following control functions:

^ Gear recognition, i.e. for A/C compressor cut-out in first gear
^ IDLE-to-DRIVE switch-over, i.e. for automatic transmissions, at speeds over 4 km/h (2.5 mph).
^ Automatic transmission protection, i.e. under 20 km/h (12.5 mph), stall speed drops to 2900 RPM after 4 seconds
^ Speed limiting, i.e. at 210 km/h (130mph).

Self-diagnosis:

^ Self-diagnosis (OBD) recognizes the fault "no signal" (Diagnostic Trouble code 1231).