A speed sensor is used to monitor speed at specific locations within the transmission system of a machine, or the ground speed of the machine. The most common measurements monitored are input speed, output speed, torque converter speed, ground speed, or cooling fan speed. Problems that can fault these sensors include debris, a failed resistor, air gap not adjusted correctly, a short circuit, an open circuit, improper mounting, or a failure of the sensor.
The following is a list of diagnostic codes that are associated with the speed sensors of the machine.
| Transmission ECM (MID 81) | ||
|---|---|---|
| DTC | Code Description | System Response |
| 190-8 | Engine Speed Sensor: Abnormal Frequency, Pulse Width, or Period | This code is activated when the ECM discovers disagreement with the transmission input speed sensor.
The code is recorded when the signal of the engine speed sensor is below the dropout value and the engine speed is above low idle. |
| 585-8 | Transmission Output Speed (TOS) Sensor #1: Abnormal Frequency, Pulse Width, or Period | The ECM determines if a problem exists by comparing the signal data between TOS 1 and TOS 2 sensors.
Transmission shifting may be harsh. |
| 669-8 | Transmission Input Speed (TIS) Sensor: Abnormal Frequency, Pulse Width, or Period | Transmission shifting may be harsh.
Shift hesitation during directional shifts. |
| 673-8 | Transmission Output Speed (TOS) Sensor #2: Abnormal Frequency, Pulse Width, or Period | The ECM determines if a problem exists by comparing the signal data between TOS 1 and TOS 2 sensors.
Transmission shifting may be harsh. |
Possible causes for an FMI 8 diagnostic code are:
- The sensor has failed.
- Intermittent connections or poor connections.
- Incorrect software is loaded to the ECM.
- The ECM has failed. ECM failure is unlikely.
| |
| Illustration 1 | g03651813 |
|
Transmission ECM J1 Speed Sensors | |
Note: The diagram above is simplified schematic of the Transmission ECM connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to: Electrical Schematic, UENR4996, "844K Wheel Dozer (T4F) Electrical System Schematic". Electrical Schematic, UENR1697, "844K Wheel Dozer (LRC) Electrical System Schematic"
Note: The Transmission Output Speed sensors do not have an adjustable gap.
Diagnostic Trouble Code Procedure
Note: Poor harness connections are often the cause of a problem in electrical circuits. Before performing any troubleshooting procedure, inspect all of the connectors involved in the circuit. Verify that all of the connections in the circuit are dry, clean, secure, and in good condition. Each pin and socket in the connectors should mate correctly when the connectors are fastened together. Check for exposed wires at the connectors for nicks or abrasion. If a problem is found with any of the connections: correct the problem and verify that the diagnostic code is still active, before performing the following procedures. For more information, refer to Troubleshooting, "Electrical Connector - Inspect".
| Troubleshooting Test Steps | Values | Results |
|---|---|---|
| 1. Identify Active DTC Code Associated With Sensor Circuit | Code present. |
FMI 8 diagnostic code, proceed to Test Step 8. |
| Begin Process For FMI 08 Troubleshooting HERE | ||
| 2. Inspect The Harness Connectors A. Turn the disconnect switch and the key start switch to the OFF position. B. Inspect all harness connections that are related to the sensor. Make sure that the connectors are clean and tight. C. Check the connectors for proper mating. Ensure that all the seals are present and in place. D. Check the harness for signs of damage or abrasion. E. Check the wires at the connector. Ensure that the wires are secured tightly into the connector. F. Perform a G. Check the exposed wires at the connectors for nicks or signs of abrasion. H. Check the connectors for moisture, dirt, or corrosion. |
The machine harness connectors are tight and free of corrosion. |
OK - The machine harness connectors are tight and free of corrosion. Proceed to Test Step 3. NOT OK - The machine harness connectors are in need of repair. Repair: Repair the machine harness or replace the machine harness. STOP |
| 3. Check The Circuit For An Open A. Turn the disconnect switch and the key start switch to the OFF position. B. Disconnect the machine harness from the sensor. C. At the machine harness connector for the sensor, install a jumper wire between contact 1 and contact 2 of the harness. D. Disconnect the machine harness connector from the ECM. E. At the machine harness connector for the ECM, measure the resistance between the positive and negative contacts for the sensor. |
There was less than 5 Ω of resistance measured. |
OK - The machine harness is correct. Proceed to Test Step 4. NOT OK - The measured resistance is greater than 5K Ω. There is an open circuit in the machine harness. The open is in the positive or negative wire for the sensor. Note: A resistance greater than 5 Ω but less than 5K Ω indicates a loose connection or corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. Repair- Repair the machine harness or replace the machine harness. |
| 4. Check The Sensor For An Open A. The disconnect switch and the key start switch remain in the OFF position. B. Remove the jumper wire that was used in the previous Test Step. C. The sensor remains disconnected from the machine harness. Insert a multimeter probe in contact 1 and contact 2 of the sensor. D. Measure the resistance of the sensor. |
The resistance should be between 600 Ω and 1800 Ω for the transmission output speed sensors.. The resistance should be between 110 Ω and 200 Ω, for the remaining sensors. |
OK - The resistance is correct for the individual speed sensor. Proceed to Test Step 5. NOT OK - The resistance is not correct according to the expected results listed in the center column. The sensor has failed. Repair: Replace the sensor. |
| 5. Check For The Active Diagnostic Code A. Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that is caused by excessive heat, battery acid, or chafing. B. Perform a C. Reconnect all harness connectors. Make sure that the connectors are fully seated. Observe that the clips for each connector are fastened securely. D. Turn the disconnect switch and the key start switch to the ON position. E. Operate the machine. F. Determine if the diagnostic code is active. |
The diagnostic code is no longer active. |
OK - The diagnostic code is no longer active. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors. Resume normal machine operation. STOP NOT OK - The diagnostic code is active. Repair: Check the circuit again. A failure of the ECM is unlikely. Exit this procedure and perform this procedure again. If the cause of the diagnostic code is not found, replace the ECM. Prior to replacing an ECM, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Troubleshooting, "ECM - Replace". |