Wheel-speed signal output
| Wheel-speed signal output |
Several other systems in the car need to be aware of the wheel speed. Therefore, the TC/ABS control module, which is not connected to the bus, has a control module output for each wheel speed signal (RL and FL are connected). A transistor in the TC/ABS control module grounds each output 29 times per wheel revolution. The output is supplied with power by the receiving system.
The main instrument unit is connected to the TC/ABS control module pin 23, the output for the rear left wheel speed signal. It converts the frequency modulated signal to km/h (mph) and corrects the value according to the programmed tyre dimension. The speed information is then distributed on the bus.
Trionic is connected to pin 25 on the TC/ABS control module and receives speed information from the front left wheel.
A voltage reading taken across any of these pins should show the values switching between 0V and B+ when the respective wheel is rotated slowly. The voltage will be 0 or B+ when the wheel is stationary. Speed information is sent even if the TC/ABS control module is out of order and the ABS, brake fluid and central warnings lamps or the TCS OFF lamp is on. The information is sent as long as the RL/FL wheel sensors are working.
For more information on wheel-speed data from the bus, see “Electrical system, Bus and diagnostics communication
” and “Electrical system, Main instrument unit
”.
Diagnostics
If the wheel-speed signal output is faulty, a DTC will be set in the receiving system.This project is supported by memberships and donations. If you use this site, please consider Joining SCNA and/or making a donation.
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