Wheel-speed signal output
Wheel-speed signal output |
The main instrument unit (MIU) receives the wheel-speed signal via a lead connected to the rear left wheel. The reason that a rear-wheel sensor has been chosen is that the distance travelled (recorded milage) can be measured more accurately on a non-driving wheel. The MIU converts the frequency-modulated signal to km/h, a computation that includes a preprogrammed correction for tyre size.
Because the MIU is connected to a bus, all the other control modules connected to the bus are able to share the RL wheel-speed and milometer (odometer) data.
The Trionic system is connected to the ABS control module via pin 26, and it receives wheel-speed data from the front right wheel.
For more information on wheel-speed data from the bus, see “Electrical system: bus and diagnostic data comms ” and “Electrical system: main instrument unit (MIU) ”.
If voltmeter measurements are made at any of the relevant terminal pins, the reading should alternate between 0 V and B+ voltage when the respective wheel is rotated slowly. Provided that the RL and FR wheel sensors are functioning, the wheel-speed signal is sent even if the ABS system is inoperative and the ABS warning light is on.