CHANNEL A 0687796 - Caterpillar

Illustration 1 g02222833
Front Differential and Right Front Axle Speed SensorThe MID 087, CID 3531 diagnostic code is associated with the Front Differential Speed Sensor. The sensor outputs a square wave frequency input signal and can determine whether the sensor is electrically connected to the Chassis ECM. When the sensor is not electrically connected to the ECM, the sensor outputs an abnormal signal to indicate a disconnected sensor.The speed sensors do not measure wheel speed directly. The sensors determine wheel speed from the measured differential case speed and the side gear speed (same speed as the axle shaft). The ECM detects the frequency of the signal change and uses the frequency to determine the speed of the wheel.The FMI 08 diagnostic fault code activates when the following conditions occur on the differential speed sensor:
An open in the power supply circuit to the speed sensor
An open in the return circuit to the speed sensor
An open in the speed sensor signal circuit to the speed sensor
A short to ground in the speed sensor signal circuit
A short to battery in the speed sensor signal circuit
The speed sensor has failed
The Chassis ECM has failed. An ECM failure is unlikelyThe inputs that impact the FMI 08 diagnostic codes are listed below:
Speed sensor
24 VDC Supply
8 VDC SupplySystem Response:
ATC is not available
The ATC will automatically engage the interaxle lock clutch when throttle and retarding are available
ATC lamp on the main cluster display will flash when the fault is active and a warning message will pop up on the CMPD.Note: The CID 3531 FMI 08 diagnostic code may be an intermittent condition.Test Step 1. CHECK FOR POWER AT THE SENSOR
Do not disconnect the harness connector from the sensor.
At the back of the harness connector for the sensor, insert a 7X-1710 Multimeter Probe along contact 1 (wire A105-OR) for the voltage supply and insert a 7X-1710 Multimeter Probe along contact 2 (wire C241-BK) for the voltage return.
Turn the key start switch and the disconnect switch to the ON position.
Measure the voltage from contact 1 (wire A105-OR) to contact 2 (wire C241-BK).Expected Result:The voltage is 8.0 0.3 VDC.Results:
OK - The voltage is 8.0 0.3 VDC. Proceed to Test Step 2.
NOT OK - The voltage is not 8.0 0.3 VDC.Repair: Confirm the following fault codes are not active on the system:
MID 087 CID 0041 FMI 03 8 VDC Supply "Voltage above normal"
MID 087 CID 0041 FMI 04 8 VDC Supply "Voltage below normal"If the fault codes are not active, repair or replace the sensor harness.STOPTest Step 2. CHECK THE SIGNAL CIRCUIT OF THE SENSOR AT THE SENSOR CONNECTOR
Turn the key start switch and the disconnect switch to the OFF position.
At the back of the harness connector for the sensor, remove the 7X-1710 Multimeter Probe from contact 1.
Insert the probe along the signal wire (contact 3).
At the back of the harness connector for the sensor, do not remove the 7X-1710 Multimeter Probe inserted in Step 1 for contact 2
Turn the disconnect switch and the key start switch to the