Vehicle Speed Signal: Description

The vehicle speed signal is transmitted from either the Self Levelling, Anti-lock Braking System (SLABS) or the ABS control module. This signal is then passed by the ECM to the automatic TCM via the CAN bus. The ECM has input diagnostics for this signal; the SLABS/ABS signal is compared to the vehicle speed signal on CAN from the automatic TCM, derived from the main gearbox output shaft speed; if the difference is greater than a threshold then a fault is detected. See Fig 1 .

Fig 1: Vehicle Speed Signal DTC Testing

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