C7.1 Engines and Generator Sets Caterpillar

Power Take-Off - Test

Usage:

C7.1 770

Note: This procedure only applies to engines equipped with Power Take-Off (PTO) switches.

Use this procedure under the following circumstances:

The correct supply voltage to the PTO switches is suspect.
Operation of the PTO switches is suspect.

Note: Some applications may only have one PTO switch.

The PTO switches provide the operator with the ability to select the desired engine speed. Engine speed will decrease with increasing load. The PTO switches can be used to control the engine speed.

The engine has the following options of set speed control:

Single speed
No speed (no PTO control)

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Illustration 1	g06154479
Schematic for the PTO switches

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Illustration 2	g01981273
View of the pin locations on the P1 connector for the PTO mode switches (18) Switch ground (41) PTO mode - disengage (56) PTO mode - ON/OFF (58) PTO mode - raise/resume (60) PTO mode - set/lower

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Table 1
Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Turn the keyswitch to the OFF position. B. Thoroughly inspect the J1/P1 connectors on the Electronic Control Module (ECM), the switch connections and battery connections. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. C. Perform a 45 N (10 lb) pull test on each of the wires in the switch connector and the ECM connector that are associated with the fault. Refer to Illustration 1. D. Check the screw for the ECM connector for the correct torque of 6 N·m (53 lb in). E. Check the harness for corrosion, abrasion, and pinch points from the PTO mode switches to the ECM.	Loose connection or damaged wire	Result: There is a fault in a connector or the wiring. Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all the seals are properly in place and ensure that the connectors are correctly coupled. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points. Proceed to Test Step 2.
2. Check the "PTO Mode Switches" on the Electronic Service Tool A. Turn the keyswitch to the OFF position. B. Connect the electronic service tool to the diagnostic connector. C. Turn the keyswitch to the ON position. D. Observe the status of the PTO mode switch on the electronic service tool while cycling the PTO ON/OFF switch. E. Use the electronic service tool to observe the status of the PTO mode switch while cycling the PTO Set/Lower switch. F. Use the electronic service tool to observe the status of the PTO mode switch while cycling the PTO Raise/Resume switch.	Switch status changes from "OPEN" to "CLOSED"	Result: The switch status changes on the electronic service tool as the PTO switches are cycled. Use the electronic service tool to clear all logged diagnostic codes. Return the engine to service. Result: The switch status does not change as the PTO switches are cycled. Proceed to Test Step 3.
3. Check the Status of the PTO Mode Disengage Switches A. Use the electronic service tool to observe the switch status while the PTO mode disengage switches are operated OFF and ON. Note: The PTO mode - Disengage switches usually function by the operation of the brake, clutch, or the operator switch. These switches should be operated separately for this test.	Switch status changes from "ENGAGED" to "DISENGAGED"	Result: The PTO mode - Disengage switch operates correctly. Use the electronic service tool to clear all logged diagnostic codes. Return the engine to service. Result: The PTO mode - Disengage switch does not operate correctly. Proceed to Test Step 4.
4. Check the Suspect PTO Switch A. Turn the keyswitch to the OFF position. B. Remove the two wires from the suspect switch. Use a suitable jumper to join the two wires together. C. Turn the keyswitch to the ON position. D. Monitor the status screen on the electronic service tool while the jumper wire is being disconnected and reconnected.	Switch status changes when jumper is installed	Result: When the jumper wire is connected, the status of the PTO mode switches is "CLOSED". When the jumper wire is disconnected, the status of the PTO mode switches is "OPEN" - The fault is in the switch. Repair: Replace the switch. Use the electronic service tool to clear all logged diagnostic codes and then verify that the repair has eliminated the problem. Result: With the jumper wire, the status of the PTO mode switches is "OPEN" or without the jumper wire, the status of the PTO mode switches is "CLOSED". Proceed to Test Step 5.
5. Measure the Resistance of the Cables at the ECM A. Turn the keyswitch to the OFF position. B. Disconnect the suspect switch. C. Disconnect the P1 connector from the ECM. D. Measure the resistance between P1:18 and the appropriate pin on the P1 connector for the suspect switch. Refer to Illustration 1. E. Repeat the procedure for each of the PTO mode switches.	Less than 2.0 Ohms with switch ON. Greater than 1k Ohm with switch off.	Result: The measured resistance is more than 2.0 Ohms with the switch ON. The measured resistance is less than 1k Ohm with the switch OFF. There is a fault with the wires between the suspect switch and the P1 connector. Repair: Repair the faulty wiring or replace the faulty wiring. Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault. Result: The measured resistance is less than 2.0 Ohms with the switch ON. The measured resistance is more than 1k Ohm with the switch OFF. Contact the Dealer Solutions Network (DSN).