Cummins ISB CM550 (1990-94) Fault Code: 241 PID: 84 SPN: 84 FMI: 2 Vehicle Speed Sensor Circuit

Circuit Description
The vehicle speed sensor (VSS) uses two separate coils of wire (some applications use a
single-coil sensor) to count gear teeth as they pass in front of the sensor. One coil is used by
the electronic control module (ECM) to sense vehicle speed. The other coil is sometimes used by the OEM to send a vehicle speed signal to the speedometer.

Component Location
The VSS is most commonly installed in the rear of the transmission.

Shop Talk
1) Disconnect the vehicle speed sensor connector that connects to the OEM speedometer,
or trip recorder, and move the truck. If the fault goes inactive, there is probably electrical noise being fed into the vehicle speed sensor circuit from the OEM device.
2) Verify the vehicle speed sensor wires in the OEM harness are twisted-pairs.
3) Check brake switch operation with INSITE™. Fault could be caused by rear-wheel lockup
without brake indication to ECM.
4) Verify the speed sensor is installed properly and its locking nut has not vibrated loose.