844K Wheel Dozer Caterpillar

Switch Circuits - Test

Usage:

844K K4Y

Transmission ECM

Operator controlled ON/OFF or momentary switches are primarily included in this information element. Two-position and three-position switches can be included under this troubleshooting title as well

The following is a list of diagnostic codes related to the switch circuits associated with the Transmission ECM.

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Table 1
Transmission ECM (MID 81)
DTC	Description	System Response
1834-2	Ignition Key Switch: Data Erratic, Intermittent, Or Incorrect	Machine start function is disabled.
3797-3	Operator Seat Belt Switch: Voltage Above Normal	Machine start function is disabled.
3797-4	Operator Seat Belt Switch: Voltage Below Normal	Machine start function is disabled.

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 signal is permanently open.
A short to battery exists in the 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 short to ground.
The switch has failed.
The ECM has failed. An ECM failure is unlikely.

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Illustration 1	g03648449
Transmission ECM wiring connection for Key Start switch.

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Illustration 2	g03649175

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Illustration 3	g03358088
This illustration is a drawing of the seat belt receptacle and associated cable for the Operator Seat Belt Switch. The switch is connected to the Transmission ECM at locations J2-52 and J2-53.

Note: The diagrams above are simplified schematics 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, UENR4996, "844K Wheel Dozer (T4F) Electrical System Schematic" for the complete schematic.Electrical Schematic, UENR1697, "844K Wheel Dozer (LRC) Electrical System Schematic" for the complete schematic.

Diagnostic Trouble Code Procedure

Note: 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.

Note: The following test procedure may create other diagnostic trouble codes. Ignore these created diagnostic trouble codes and clear the diagnostic trouble codes when the original diagnostic trouble code has been corrected.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Identify Active FMI Code Associated With The Switch 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 8.
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 is as expected. 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 Harness A. The disconnect switch and key start switch remain in the OFF position. B. Inspect the harness. C. Check the connectors for proper mating. D. Check the exposed wires for nicks and abrasions. E. Check for moisture, dirt, or corrosion at connector locations.	The harness appears to be correct.	OK - The harness appears correct. Proceed to Test Step 10. NOT OK - The harness appears to be damaged. Repair: Repair the machine harness ot replace the machine harness. STOP
Begin Process For FMI 3 Troubleshooting HERE
5. Check The Signal Circuits For An Open A. Turn the disconnect switch and the key start switch to the OFF position. B. Disconnect the J1 machine harness connector from the ECM. C. At the J1 harness connector, measure the resistance from the Normally Open contact to the ground contact with the switch in the Normally Open position. The switch is pressed. D. At the J1 harness connector, measure the resistance from the Normally Closed contact to the ground contact with the switch in the Normally Closed position. The switch is not pressed.	Open resistance should be greater than 5K Ω. Closed resistance should be less than 5 Ω. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged.	OK - The measurements are correct. Proceed to Test Step 6. NOT OK - One or more of the measurements was incorrect. Repair: 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
6. Check The Resistance Of The Switch A. Measure the resistance from the normally open contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes. B. Measure the resistance from the normally closed contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes.	Open resistance should be greater than 5K Ω. Closed resistance should be less than 5 Ω. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged.	OK - The measurements are correct. Proceed to Test Step 7. NOT OK - One or more of the measurements was incorrect. Repair: Replace the switch. Verity that the new switch corrects 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 circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. STOP
7. Check the Ground Circuit Of The Switch In The Harness A. Turn key start switch and disconnect switch OFF. B. Disconnect the switch from the machine harness. C. Measure the resistance between the return contact on the harness to ground.	The resistance is less than 5 Ω.	OK - The circuit is correct. Proceed to Test Step 10. NOT OK - The resistance is greater than 5K Ω. The circuit is open. Repair: 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
Begin Process For FMI 4 Troubleshooting HERE
8. Check The Switch A. Measure the resistance from the normally open contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes. B. Measure the resistance from the normally closed contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes.	Open resistance should be greater than 5K Ω. Closed resistance should be less than 5 Ω. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged.	OK - The measurements are correct. Proceed to Test Step 9. NOT OK - One or more of the measurements was incorrect. Repair: Replace the switch. Verity that the new switch corrects 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 circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit. STOP
9. Check The Signal Circuits For An Open A. Reconnect the switch to the machine harness. B. Repeat Test Step 7, however instead of measuring the resistance from the switch contacts, measure from the corresponding contacts on the ECM harness.	Open resistance should be greater than 5K Ω. Closed resistance should be less than 5 Ω. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged.	OK - The measurements are correct. Proceed to Test Step 10. NOT OK - One or more of the measurements was incorrect. Repair: 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
10. 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 still active. Repair: Check the status of the diagnostic code. If the cause of the problem is not found, the ECM may require replacement. Prior to replacing the ECM, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, see Troubleshooting, "ECM - Replace" STOP NOT OK - The continuity check is not correct. Repair: There is an open in the signal circuits of the machine harness. Repair or replace the machine harness. STOP