621K OEM Wheel Tractor-Scraper Operator Control Switch (Switch to Ground)

Operator Control Switch (Switch to Ground) - Test

621K OEM Wheel Tractor-Scraper [UENR5941]

621K OEM Wheel Tractor-Scraper Indicator Lamp - Test

621K OEM Wheel Tractor-Scraper Relay - Test

ELECTRICAL AND STARTING SYSTEM

SWITCH GP

621K OEM Wheel Tractor-Scraper Condition Switch (Two Wire) - Test

621K OEM Wheel Tractor-Scraper Operator Control Switch (Switch to Ground) - Test

621K OEM Wheel Tractor-Scraper Relay - Test

621K OEM Wheel Tractor-Scraper Switch Circuits - Test

1.1. Implement ECM

2.1. Transmission/Chassis ECM

3.1. Diagnostic Trouble Code Procedure

Implement ECM

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Table 1
Implement ECM (MID 82)
DTC	Code Description	System Response
490-3	Implement Lockout Switch : Voltage Above Normal	Switch may be inoperable.
490-4	Implement Lockout Switch : Voltage Below Normal	Switch may be inoperable.

Transmission/Chassis ECM

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Table 2
Transmission/Chassis ECM (MID 27)
DTC	Code Description	System Response
70-2	Parking Brake Switch : Erratic, Intermittent, or Incorrect	Parking Brake will not release.
788-2	Engine Retarder Selection Switch : Erratic, Intermittent, or Incorrect	Retarder Switch will not engage.
1046-3	Power train Oil Filter Bypass Switch : Voltage Above Normal	Bypass switch will not function when required.
1292-3	Gear Hold Switch : Voltage Above Normal	The gear hold function will be inoperable.
1292-4	Gear Hold Switch : Voltage Below Normal	The gear hold function will be inoperable.
3629-3	Left Ladder Position Proximity Switch : Voltage Above Normal	The indicator for the ladder will display that the ladder is not in the UP position. The alarm will sound.
3629-4	Left Ladder Position Proximity Switch : Voltage Below Normal	The indicator for the ladder will display that the ladder is not in the UP position. The alarm will sound.
3797-3	Operator Seat Belt Switch : Voltage Above Normal	Operator is unable to start machine.
3797-4	Operator Seat Belt Switch : Voltage Below Normal	Operator is unable to start machine.

Possible Causes for an FMI 2 Diagnostic code are:

A short circuit exists.
An open circuit exists.
The switch has failed.
The ECM has failed. A failure of the ECM is unlikely.

Possible Causes for an FMI 3 Diagnostic code are:

The ground wire is open.
A wire is shorted to another circuit.
The switch has failed.
The ECM has failed. A failure of the ECM is unlikely.

Possible Causes for an FMI 4 Diagnostic code are:

A wire is shorted to ground.
The switch has failed.
The ECM has failed. A failure of the ECM is unlikely.

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Table 3
Status of Transmission/Chassis Gear Hold Switch
Gear Hold Switch	Switch Position	Circuit
Released	Up	Open
Pressed	Down	Closed

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Table 4
Status of "Ladder Poxition Proximity" Switch Contact
Ladder Extended	N/O Input J1-34 (wire E457-GY)	N/C InputJ1-35 (wire E788-BU)
Ladder Retracted	Open⁽¹⁾	Closed⁽²⁾
"Ladder Position" Switch	Open	Closed

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⁽¹⁾	Open to ECM return J2-22 (J766-PU - ground)
⁽²⁾	Closed to ECM return J2-22 (J766-PU - ground)

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Illustration 1	g03320169
Transmission ECM Switch-To-Ground Connections

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Illustration 2	g03350155
Implement ECM Switch-To-Ground Connections

Note: Before performing this procedure, inspect the harness connectors that are involved in the 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. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure. Refer to the list below to identify the correct schematic for your machine.

Electrical Schematic, UENR2689 for the 621K Tractor/Scraper.

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 diagnostic code is still active, before performing the following procedures. For more information, refer to Troubleshooting, "Electrical Connector - Inspect".

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Table 5
Troubleshooting Test Steps	Values	Results
1. Identify Active FMI Code Associated With Sensor Circuit.	Code present.	FMI 2 diagnostic code, proceed to Test Step 2. FMI 3 diagnostic code, proceed to Test Step 5. FMI 4 diagnostic code, proceed to Test Step 10.
Begin Process For FMI 2 Troubleshooting HERE
2. Check The Switch. A. Turn the disconnect switch and the key start switch OFF. B. Disconnect the switch from the machine harness. C. Measure the resistance between the return or ground pin and all input pins, one at a time. D. Move the switch through the range of selections, and verify continuity.	The resistance should be less than 5 Ω when switch operation indicates continuity, and greater than 5K Ω when switch operation indicates no continuity.	OK - The resistance meets expectations. Proceed to Test Step 3. NOT OK - The resistance is not as expected. Repair: Replace the switch. Verify that the new switch resolves the diagnostic code. 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 switch. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. STOP
3. Check The Circuit For An Open. A. Turn the disconnect switch and the key start switch OFF. B. Disconnect the switch and ECM from the machine harness. C. Use a jumper wire between each contact on the machine harness at the switch end, one at a time. D. Measure the resistance at the corresponding ECM harness pins.	The resistance is less than 5 Ω.	OK - The resistance is less than 5 Ω. Proceed to Test Step 4. NOT OK - The resistance is greater than 5K Ω. Repair: The circuit wire is open in the machine harness. Repair or replace the machine harness. 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
4. Check The Circuit For A Short. A. The harness connectors for the switch and ECM remain disconnected. B. Remove any jumper wires used from a previous test step. C. At the machine harness connector for the ECM measure the resistance between the signal circuits and every other contact in the wiring harness.	The resistance is greater than 5K Ω.	OK - The resistance is correct. Proceed to Test Step 10. NOT OK - The resistance check is not correct. Repair: There is a short in the signal circuits of the machine harness. Repair or replace the machine harness. STOP
Begin Process For FMI 3 Troubleshooting HERE
5. Check The Harness For An Open. A. Turn key start switch and disconnect switch OFF. B. Disconnect the switch from the machine harness. C. Disconnect the J1 and J2 machine harness connectors at the ECM. D. At the machine harness connector for the switch, place a jumper between the two signal wires at the switch connector. Check for low resistance at the ECM connector. E. At the machine harness connect for the ECM, measure the resistance between the "NORMALLY OPEN" and "NORMALLY CLOSED" contacts for the switch.	The resistance is less than 5 Ω.	OK - The circuit is correct. Proceed to Test Step 6. NOT OK - The resistance is greater than 5K Ω. One or both of the input wires to the circuit is open or has a poor connection. Repair: Check the continuity of each input wire individually. Refer to the schematic for your machine. Check all connectors to insure the couplings are good, clean, and secure. Check the wiring harness for locations where the bundle could be damaged by chaffing or crush points. If needed, repair or replace the machine harness. Note: A resistance that is greater than 5 Ω but less than 5K Ω indicates a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω indicates an open in the circuit. STOP
6. Check The Ground Source For The Switch. A. The key start switch and disconnect switch remain OFF. B. All harness connectors remain disconnected. C. At the machine harness connector for the switch, connect a jumper wire between the common ground contact and the NORMALLY CLOSED (N/C) contact. D. At the J1 and J2 harness connector for the ECM, measure the resistance between common ground and the N/C contact.	The resistance is less than 5 Ω.	OK - The resistance is less than 5 Ω. The circuit for the common ground is not open in the machine harness. Proceed to Test Step 7. NOT OK - The resistance is greater than 5K Ω. The circuit for the common ground is open or has a poor connection. Repair: There is an open or poor connection in the ground wire of the switch. Confirm that no problems exist at the electrical connections for the circuit. (Refer to the complete electrical schematic for your machine for connector locations.) Repair or replace the harness if crimp points or chaffing have damaged the wiring harness. Note: A resistance that is greater than 5 Ω but less than 5K Ω indicates a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω indicates an open in the circuit. STOP
7. Check The Harness For A Short. A. The key switch and disconnect switch remain OFF. B. All harness connectors remain disconnected. C. Remove the jumper wire installed in the previous step. D. At the machine harness connector for the ECM, measure resistance between the NORMALLY CLOSED (N/C) contacts and all other contacts of the J1 and J2 harness connectors. E. At the machine harness connector for the ECM, measure resistance between the NORMALLY OPEN (N/O) contacts and all other contacts of the J1 and J2 harness connectors.	The resistances are greater than 5K Ω.	OK - The resistance is greater than 5K Ω. The harness circuit is correct. Proceed to Test Step 8. NOT OK- The resistance less than 5 Ω. Repair: A short exists in the harness between the signal circuit and the wire with the low resistance reading. Repair or replace the machine harness. 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
8. Check the Operation of the Switch. Note- The switch remains disconnected from the machine harness. The disconnect switch and the key start switch remain in the OFF position. A. At the connector for the switch, measure the resistance (continuity) between the common contact and the switch N/C contact 2. Measure this resistance as the switch is engaged and disengaged. B. At the connector for the switch, measure the resistance (continuity) between the common contact and the switch N/O contact 2. Measure this resistance as the switch is engaged and disengaged.	The continuity checks of the switch agree with the table at the beginning of this procedure.	OK - The switch is operating correctly. Proceed to Test Step 9. NOT OK - The switch is not operating correctly. The switch has failed. Repair: Replace the switch. After replacement of the switch, verify that the operation of the new switch is correct before operating the machine. STOP
9. Check The Operation Of The ECM. A. The key start switch and disconnect switch remain OFF. B. Reconnect all harness connections. C. Using a wire removal tool, remove the signal wires and socket from the machine harness connector to the switch. D. Turn the key start switch and disconnect switch ON. E. Use a multimeter probe to contact both signal wire pins through the empty space in the harness connector. F. Ground the other end of the multimeter probe to frame ground. G. .Observe the status of the diagnostic code.	The FMI 3 changes to an FMI 4.	OK - The ECM is operating correctly. The diagnostic code is no longer active. The diagnostic code may have been caused by an intermittent problem. If the problem cannot be readily identified, return the machine to service and monitor for any reoccurrence. STOP NOT OK - The FMI 3 diagnostic code remains active. The ECM may have failed. Prior to replacing the ECM, always contact the Technical Communicator at your dealership for possible consultation with AVSpare ^®. This consultation may greatly reduce repair time. If the ECM requires replacement, see Troubleshooting, "ECM - Replace" STOP
Begin Process For FMI 4 Troubleshooting HERE
10. Check The Switch. A. Turn the key start switch and disconnect switch ON. B. Ensure that the diagnostic code is active. C. Connect a laptop, with the latest version of Cat^® ET, to the machine. Use the Cat ET program on the laptop to monitor the status of the diagnostic code. D. Observe the status of the diagnostic code while the connector of the switch is disconnected from the machine harness. Reconnect the switch and disconnect the switch again. Observe the status of the diagnostic code.	The FMI 4 diagnostic code remains active at all times during the check of the switch.	OK - The FMI 4 diagnostic code remains active during the check of the switch. Proceed to Test Step 11. NOT OK - The FMI 4 changes to an FMI 3 as the switch is disconnected from the harness. The switch has failed. Repair: Replace the switch. Verity that the new switch corrects the diagnostic code. STOP
11. Check the Harness for a Short. Note- The switch remains disconnected from the machine harness. A. The key start switch and disconnect switch remain OFF. B. Unplug the J1 and J2 machine harness connectors from the ECM. C. At the machine harness connector for the ECM, measure resistance between the NORMALLY CLOSED (N/C) signal contact and all other contacts used in the J1 and J2 harness connectors. D. At the machine harness connector for the ECM, measure resistance between the NORMALLY OPEN (N/O) signal contact and all other contacts used in the J1 and J2 harness connectors.	Each resistance is greater than 5K Ω.	OK - Each resistance is greater than 5K Ω. The input circuits of the switch are not shorted in the machine harness. Proceed to Test Step 12. NOT OK- One or more resistance measurements are less than 5 Ω. Repair: A short exists in the harness between the signal circuit and the wire with the low resistance reading. Refer to the schematic listed above for your machine. Repair or replace the machine harness. 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
12. Check the Operation of the Switch. A. The key start switch remains OFF. B. Check the operation of the switch. Refer to the table for the suspected faulty switch at the beginning of this procedure for switch operation.	The switch operates correctly.	OK - The switch is operating correctly. Proceed to Test Step 13. NOT OK - The switch is not operating correctly. The switch has failed. Repair: Replace the switch. STOP
13. 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. C. Reconnect all harness connectors. D. Turn key start switch and disconnect switch ON. E. Operate the machine. F. Check the status of the diagnostic code.	The diagnostic code is not active.	OK - The diagnostic code is not active. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor connection or a short at one of the connectors that was disconnected and reconnected. Resume normal operation. STOP NOT OK- The diagnostic code is active. Check the circuit again. Repair- If the cause of the problem is not found, the ECM may have failed. Prior to replacing an ECM, always contact the Technical Communicator at your dealership for possible consultation with AVSpare. This consultation may greatly reduce repair time. If the cause of the diagnostic code is not found, replace the ECM that has activated the diagnostic code. Refer to Troubleshooting, "ECM - Replace". STOP