Operation and Vehicle Speed

The ABS control module sends a vehicle speed signal to pin 39 of the Trionic ECM. The signal is a square-wave which varies between 0 V and Batt+ 29 times/wheel rotation. This speed signal is used to:
^ decide which gear is engaged at the time
^ activate the SHIFT UP lamp (does not apply to 5th gear)
^ limit the boost pressure in Reverse, 1st and 2nd gears
^ activate fuel shut-off in 3rd, 4th and 5th gears
^ activate speed limiting (by limiting the boost pressure at 230 km/h)

If there is no speed signal, the above functions do not occur and the boost pressure, on cars with manual transmission, is limited.