Condition Switch (Two Wire) - Test
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| Transmission ECM (MID 81) | ||
|---|---|---|
| DTC | Code Description | System Response |
| 793-3 | Primary Steering Pressure Switch : Voltage Above Normal | All implement commands are still allowed |
| 793-4 | Primary Steering Pressure Switch : Voltage Below Normal | |
| 794-3 | Secondary Steering Pressure Switch : Voltage Above Normal | |
| 794-4 | Secondary Steering Pressure Switch : Voltage Below Normal | |
| 794-7 | Secondary Steering Pressure Switch : Not Responding | |
The 793 DTC and the 794 DTC can only be recorded if the optional secondary steering system is installed. The primary steering pressure switch is connected to two inputs of the ECM. One contact is open and the other contact is grounded during proper operation.
Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure, and in good condition. Check the wiring for pinch points or abrasions. Look for and repair areas that indicate wires are exposed. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing a troubleshooting procedure.
Possible Causes for an FMI 3 Diagnostic code are:
- The ground source is bad.
- A signal is permanently open.
- The switch has failed.
- The ECM has failed. A failure of the Transmission ECM is unlikely.
The ECM has determined that both contacts are open.
Possible Causes for an FMI 4 are:
- A short to ground.
- The switch has failed.
- The ECM has failed. A failure of the Transmission ECM is unlikely.
The ECM has determined that both contacts are grounded.
Possible Causes for an FMI 7 are:
- There is secondary steering pressure when the relay is deactivated
Note: The DTC 794-7 cannot be deactivated until the secondary steering system is activated and the secondary steering pressure switch indicates that there is pressure in the system.
Note: The secondary steering motor requires a large amount of current. A weak battery may have an effect on the operation of the motor.
Note: If the switch is failed to ground, then the power train ECM believes that the operator is manually turning on the secondary steering system. If the pressure switch for the secondary steering system is not indicating pressure, then the CID 0794 FMI 07 diagnostic code will be active.
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| Illustration 1 | g03376242 |
Schematic of the pressure switch circuits associated with the ECM. | |
Note: The diagram above is a simplified schematic of the ECM switch connections. The schematic is electrically correct, however, not all of the possible harness connectors are shown. Refer to the latest revision of Electrical Schematic, UENR1687 for the complete schematic of 966H and 972H Wheel Loaders Electrical System. Refer to the latest revision of Electrical Schematic, UENR1699 for the complete schematic of 980H Wheel Loaders Electrical System.
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| Primary Steering Pressure Switch | ||
|---|---|---|
| Switch Position | 417-GY Circuit N/O J2-37 |
484-YL Circuit N/C J2-38 |
| Low Pressure | Open | Closed |
| High Pressure | Closed | Open |
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| Secondary Steering Pressure Switch | ||
|---|---|---|
| Switch Position | 453-PK Circuit N/O J2-60 |
416-OR Circuit N/C J2-61 |
| Low Pressure | Open | Closed |
| High Pressure | Closed | Open |
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| Troubleshooting Test Steps | Values | Results |
|---|---|---|
| 1. Identify Active FMI Code Associated With Sensor Circuit | Code present. |
FMI 3 diagnostic code, proceed to Test Step 2. FMI 4 diagnostic code, proceed to Test Step 8. FMI 7 diagnostic code, proceed to Test Step 12. |
| Begin Process For FMI 3 Troubleshooting HERE | ||
| 2. Check the Ground Source A. Turn the key start switch and the disconnect switch to the OFF position. B. Disconnect the machine harness connector from the switch. D. At the machine harness connector for the switch, measure resistance between the ground contact and frame ground. |
The resistance is less than 5 Ω. |
OK - The resistance is less than 5 Ω. The ground circuit is good. Proceed to Test Step 3. NOT OK- The resistance greater than 5K Ω. The ground source is not good. Repair: Repair or replace the machine harness for the ground. Note: A resistance that is greater than 5 Ω but less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. STOP |
| 3. Check The Switch Circuits For A Short To The +Battery Circuit A. The disconnect switch and the key start switch remain in the OFF position. B. The machine harness connector remains disconnected from the switch. C. Disconnect the J1 and J2 machine harness connector. D. At the machine harness connector for the ECM, measure the resistance from the (N/O) contact and the (N/C) contact of the machine harness to all the contacts that are used in the machine harness connectors for the ECM. |
The resistance is greater than 5 K Ω. |
OK - The resistance is greater than 5 K Ω. Proceed to Test Step 4. NOT OK - One or more of the resistance measurements were less than 5 Ω. There is a short in the machine harness. Repair: Repair or replace the machine harness. Note: A resistance that is greater than 5 Ω but less than 5 K Ω indicates a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5 K Ω indicates an open in the circuit. STOP |
| 4. Check the Harness For an Open A. The disconnect switch and the key start switch remain in the OFF position. B. The machine harness remains disconnected from the ECM and the switch. C. At the machine harness connector for the switch, place a jumper wire between the (N/O) contact and the (N/C) contact . E. At the machine harness connector for the ECM, measure the resistance between the (N/O) contact and the (N/C) contact. |
The resistance is less than 5 Ω. |
OK - The resistance is less than 5 Ω. The circuit is correct. Proceed to Test Step 5. NOT OK - The resistance is greater than 5 K Ω. The circuit is open. Repair: Repair or replace the machine harness. Note: A resistance that is greater than 5 Ω but less than 5 K Ω indicates a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5 K Ω indicates an open in the circuit. STOP |
| 5. Check The Operation Of The Switch (Low Pressure) Do NOT run the engine during this Test Step. This will cause low system pressure to the primary steering pressure switch. A. The disconnect switch and the key start switch remain in the OFF position. B. Remove the jumper that was installed in the previous Test Step. C. The machine harness remains disconnected from the switch. D. Reconnect the machine harness to the ECM. E. Connect one lead from a multimeter to contact A ) of the harness connector for the switch. F. Connect the other lead from a multimeter to contact B of the harness connector for the switch. G. Measure the resistance between contact A and contact B. Note the resistance. H. Disconnect the lead from contact B and connect the lead to contact C . I. Measure the resistance between contact A and contact C. Note the resistance. |
The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. |
OK - The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. Proceed to test step 6. Repair: The switch is faulty. Replace the switch. STOP NOT OK - The resistance from contact A to contact C is not less than 5 Ω, or the resistance from contact A to contact B is not greater than 5 K Ω. The switch has failed. STOP |
| 6. Check The Operation Of The Switch (High Pressure) A. Turn the disconnect switch and the key start switch to the ON position. B. Start the engine. This will cause the system pressure to activate the primary steering pressure switch. C. Reconnect the machine harness to the ECM. D. Connect one lead from a multimeter to contact A ) of the harness connector for the switch. E. Connect the other lead from a multimeter to contact B of the harness connector for the switch. F. Measure the resistance between contact A and contact B. Note the resistance. G. Disconnect the lead from contact B and connect the lead to contact C . H. Measure the resistance between contact A and contact C. Note the resistance. |
The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. |
OK - The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. Proceed to test step 12. Repair: The switch is faulty. Replace the switch. STOP NOT OK - The resistance from contact A to contact C is not less than 5 Ω, or the resistance from contact A to contact B is not greater than 5 K Ω. The switch has failed. STOP |
| Begin Process For FMI 4 Troubleshooting HERE | ||
| 7. Check The Switch A. Turn the key start switch and the disconnect switch to the OFF position. B. Disconnect the machine harness connector from the switch. C. Turn the key start switch and the disconnect switch to the ON position. D. At the machine harness connector for the switch, measure resistance between the ground contact and frame ground. |
The DTC 793 - 4 has been replaced by DTC 793 - 3. |
OK - The DTC 793 - 4 has been replaced by DTC 793 - 3. The machine harness and the ECM are correct. Proceed to Test Step 9. NOT OK- The DTC 793 - 4 is still active. Proceed to Test Step 8. |
| 8. Check The Harness A. Turn the key start switch and the disconnect switch to the OFF position. B. The machine harness connector remains disconnected from the switch. C. Disconnect the J1 and J2 machine harness connector from the ECM. D. At the machine harness connector for the ECM, measure the resistance from the (N/O) contact and the (N/C) contact of the machine harness to all the contacts that are used in the machine harness connectors for the ECM. |
Each resistance is greater than 5 K Ω. |
OK - Each resistance is greater than 5 K Ω. The ECM has failed Repair: Prior to replacing the ECM, contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, refer to Troubleshooting, "ECM - Replace" STOP NOT OK - One or more of the resistance measurements were less than 5 Ω. There is a short in the machine harness. Repair: Repair or replace the machine harness. STOP |
| 9. Check The Operation Of The Switch (Low Pressure) Do NOT run the engine during this Test Step. This will cause low system pressure to the primary steering pressure switch. A. The disconnect switch and the key start switch remain in the OFF position. B. Remove the jumper that was installed in the previous Test Step. C. The machine harness remains disconnected from the switch. D. Reconnect the machine harness to the ECM. E. Connect one lead from a multimeter to contact A ) of the harness connector for the switch. F. Connect the other lead from a multimeter to contact B of the harness connector for the switch. G. Measure the resistance between contact A and contact B. Note the resistance. H. Disconnect the lead from contact B and connect the lead to contact C . I. Measure the resistance between contact A and contact C. Note the resistance. |
The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. |
OK - The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. Proceed to test step 10. Repair: The switch is faulty. Replace the switch. STOP NOT OK - The resistance from contact A to contact C is not less than 5 Ω, or the resistance from contact A to contact B is not greater than 5 K Ω. The switch has failed. STOP |
| 10. Check The Operation Of The Switch (High Pressure) A. Turn the disconnect switch and the key start switch to the ON position. B. Start the engine. This will cause the system pressure to activate the primary steering pressure switch. C. Reconnect the machine harness to the ECM. D. Connect one lead from a multimeter to contact A ) of the harness connector for the switch. E. Connect the other lead from a multimeter to contact B of the harness connector for the switch. F. Measure the resistance between contact A and contact B. Note the resistance. G. Disconnect the lead from contact B and connect the lead to contact C . H. Measure the resistance between contact A and contact C. Note the resistance. |
The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. |
OK - The resistance from contact A to contact C is less than 5 Ω, and the resistance from contact A to contact B is greater than 5 K Ω. Proceed to test step 11. Repair: The switch is faulty. Replace the switch. STOP NOT OK - The resistance from contact A to contact C is not less than 5 Ω, or the resistance from contact A to contact B is not greater than 5 K Ω. The switch has failed. STOP |
| 11. Check If The Diagnostic Code Remains A. Inspect the harness connectors and clean the contacts of the harness connectors. B. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit. B. Reconnect all harness connectors. C. Turn key start switch and disconnect switch ON. D. Operate the machine. Check the status of the diagnostic code. |
The diagnostic code is not active. |
OK - The diagnostic code is not active. Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation. STOP NOT OK - The diagnostic code is still active. The ECM may have failed. Repair: Prior to replacing the ECM, contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, refer to Troubleshooting, "ECM - Replace" STOP |
| Begin Process For FMI 7 Troubleshooting HERE | ||
| 12. Check The Status Of The Diagnostic Code A. Start the engine. B. Press and hold the secondary steering test switch for 5 to 10 seconds. B. Reconnect all harness connectors. C. Check the status of the DTC 794-7. |
The DTC indicator is not active and the DTC is not active. |
OK - The DTC indicator is not active and the DTC is not active. Repair: Repeat this test to verify the result. STOP NOT OK - The DTC indicator remains active and the DTC remains active. The harness has failed or the ECM has failed. Proceed to test step 12. |
| 13. Check For Other Recorded DTCs Other recorded diagnostic codes may indicate the reason for the improper operation of the secondary steering system. A. Check for other recorded DTCs. B. Press and hold the secondary steering test switch for 5 to 10 seconds. B. Reconnect all harness connectors. C. Check the status of the DTC 794-7. |
There are NOT any other recorded DTCs |
OK - There are NOT any other recorded DTCs Proceed to test step 14. NOT OK - There are other recorded diagnostic codes. Repair: Exit the DTC 794-7procedure. Correct the other recorded diagnostic codes. Return to the DTC 794-7 procedure after the other recorded diagnostic codes are corrected. |
| 14. Check The Battery Voltage A.Check the battery voltage. |
The battery voltage is correct. |
OK - The battery voltage is correct. Proceed to test step 15. NOT OK - The battery voltage is NOT correct. Repair: Correct the cause of the low battery voltage and verify that the battery voltage is correct. If the conditions are not resolved, continue. Proceed to Step 15. |
| 15. Check The Secondary Steering Test Switch A. Check the secondary steering test switch. |
The secondary steering test switch is correct. |
OK - The secondary steering test switch is correct. Proceed to test step 16. NOT OK - The secondary steering test switch is not correct .Repair: Repair the harness or the cause of the failed circuit. STOP. |
| 16. Check The Secondary Steering Pressure A. Check the secondary steering pressure. |
The secondary steering pressure is correct. |
OK - The secondary steering pressure is correct. Repair: Exit this procedure. Use the procedure for DTC 794-3 and DTC 794-4 to verify that the secondary steering pressure switch is operational. NOT OK - The secondary steering pressure is not correct. Repair the harness or the cause of the failed circuit. STOP. |
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