C27 and C32 Engines for Caterpillar Built Machines Caterpillar

Speed Control - Test

Usage:

990K A9P

Use this procedure to troubleshoot the electrical system if a problem is suspected with the throttle switch.

Show/hide table




Illustration 1	g02310333
Location of the throttle switch

The throttle switch provides the operator with the ability to select the desired engine speed. The throttle switch is a three-position momentary rocker switch. The three positions are Neutral, Rabbit, and Tortoise. The throttle switch can be used to select high idle or low idle. The throttle switch can also be used to adjust the maximum engine speed.

High Idle - To increase engine speed to the high idle, push the top of the switch (Rabbit) one time and release the switch.

Low Idle - To decrease engine speed to the low idle, push the bottom of the switch (Tortoise) one time and release the switch.

Set Maximum Speed - Set the engine speed to high idle. Push the decelerator pedal until the desired speed is reached. When this desired speed is reached, push the top of the throttle control switch and hold for 3 seconds. The current engine speed will be electronically set as the maximum operating speed. The decelerator will function normally in order to reduce engine speeds below this maximum speed. In order to return to high idle as maximum speed, press the top part of the throttle control switch.

The throttle switch is connected to the four throttle inputs of the ECM. Each position generates a specific on/off pattern on the throttle inputs. A diagnostic code is generated if a pattern that does not correspond with any of the switch positions is detected.

Voltage at the inputs to the ECM for the throttle switch is 7.5 ± 0.5 VDC when the throttle inputs are open. The voltage is less than 0.5 VDC when the throttle inputs are closed.

Caterpillar Electronic Technician (ET) can be used to view the status of the inputs for the throttle switch.

Show/hide table




Illustration 2	g02305993
Schematic for the throttle switch

Show/hide table

Table 1
Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the main disconnect switch to the OFF position. B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for additional information. C. Perform a 45 N (10 lb) pull test on the connector wires. D. Check the harness for abrasions and pinch points.	Connectors and Wiring	Result: The connectors and wiring appear to be OK. Proceed to Test Step 2. Result: There is a problem with the connectors and/or wiring. Repair: Repair or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. If the problem is not resolved, proceed to Test Step 2.

Show/hide table

Table 2
Throttle Input at the ECM	Neutral	Rabbit	Tortoise
#1 (tortoise N/O contacts)	Off	Off	On
#2 (tortoise N/C contacts)	On	Off	On
#3 (rabbit N/O contacts)	Off	On	Off
#4 (rabbit N/C contacts)	On	On	Off

Show/hide table

Table 3
Troubleshooting Test Steps	Values	Results
2. Check the Status of the Throttle Inputs on Cat ET A. Connect Cat ET to the service tool connector. B. Turn the keyswitch to the ON position. C. Observe the status of the throttle inputs on Cat ET while you operate the throttle switch in each position.	Throttle Switch	Result: The status of the throttle switch is correct. Repair: The throttle switch is functioning properly at this time. There may be an intermittent electrical problem in the wiring harness or in a connector. If an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for troubleshooting information. If the repair does not resolve the problem, proceed to Test Step 3. Result: One or more of the inputs is incorrect. There is a problem in the circuit for the throttle switch. Proceed to Test Step 3.

Show/hide table

Table 4
Throttle Input at the ECM	Neutral	Rabbit	Tortoise
#1 (tortoise N/O contacts)	Off	Off	On
#2 (tortoise N/C contacts)	On	Off	On
#3 (rabbit N/O contacts)	Off	On	Off
#4 (rabbit N/C contacts)	On	On	Off

Show/hide table

Table 5
Troubleshooting Test Steps	Values	Results
3. Check the Harness between the Throttle Switch and the ECM A. Turn the keyswitch to the OFF position. B. Fabricate two jumper wires that are long enough to create a short circuit across the connector for the throttle switch. Crimp spade terminals to each end of the jumper wires. C. Disconnect the wires for the suspect throttle inputs from the throttle switch. Refer to Table above. a. Turn the keyswitch to the ON position. b. Check the status of the suspect throttle inputs on Cat ET. c. Use the jumper wires to short the wires for the suspect throttle inputs to the return wire at the switch. d. Monitor the status of the suspect throttle inputs on Cat ET. D. Turn the keyswitch to the OFF position. E. Remove the jumper wires. Reconnect all wires to the original configuration.	Suspect Throttle Inputs	Result: The harness and the ECM are OK. Repair: There is a problem with the throttle switch. Replace the switch. Verify that the repair eliminates the problem. If the repair does not eliminate the problem, proceed to Test Step 4. Result: The status for the suspect throttle inputs does not change when the jumper wires are installed. Verify that the return circuit for the throttle switch is continuous to chassis ground. Ensure that the return circuit has a good connection to the chassis ground. Proceed to Test Step 4.

Show/hide table

Table 6
Terminal location at the ECM	Neutral	High "Rabbit"	Low "Tortoise"
P1-22	Off	Off	On
P1-23	On	Off	On
P1-40	Off	On	Off
P1-41	On	On	Off

Show/hide table

Table 7
Troubleshooting Test Steps	Values	Results
4. Check the Operation of the ECM A. Disconnect the J1/P1 ECM connector. B. Fabricate two jumper wires that are long enough to create a short between the ECM connector and engine ground. Crimp a connector socket to one end of each of the jumper wires. C. Remove the wires for the suspect throttle inputs from the appropriate terminals at the P1 ECM connector. D. Connect the J1/P1 ECM connector. E. Turn the keyswitch to the ON position. F. Check the status of the suspect throttle inputs on Cat ET. a. Use the two jumper wires to short the terminals for the suspect throttle inputs to engine ground. Refer to the Table above. b. Monitor the status of the suspect throttle inputs on Cat ET. G. Remove the jumper wires. Reconnect all wires and connectors to the original configuration.	Suspect Throttle Input	Result: The status for the suspect throttle input changes correctly. Repair: There is either an open circuit or a short circuit in the wiring between the ECM and the throttle switch. Repair the wiring harness. Verify that the repair eliminates the problem. Result: The status for the suspect throttle inputs does not change correctly. Repair: The ECM is not responding to the switch inputs. There appears to be a problem with the ECM. Before you consider replacing the ECM, consult the Dealer Solutions Network (DSN) for assistance.