3176C Engines for Caterpillar Built Machines Caterpillar

Use this procedure to troubleshoot any suspect problems with the throttle switch.

This procedure covers the following diagnostic code:

• 91-02 Incorrect Throttle Switch inputs

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 high idle, push the top of the switch (Rabbit) one time and release the switch.

Low Idle - To decrease engine speed to 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 on the decelerator pedal until the desired speed is reached. When this desired speed is reached, push on the top of the throttle control switch and hold for three seconds. This will electronically set the current engine speed 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 Electronic Control Module (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.

Once a diagnostic code is generated, the ECM ignores the throttle input signals and the desired engine speed is set to 1000 rpm, unless the actual engine speed is below 1000 rpm. If the actual engine speed is below 1000 rpm, the desired engine speed is set to the current engine speed. The desired engine speed is set to low idle if the engine is not running.

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.

Illustration 1	g01280401
Schematic for the throttle switch

Test Step 1. Inspect Electrical Connectors and Wiring

1. Remove the electrical power from the ECM.

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Illustration 2	g01183529
Location of the J1/P1 ECM connector (typical left side engine view)

2. Thoroughly inspect the J1/P1 ECM connector. Refer to diagnostic functional tests Troubleshooting, "Electrical Connectors - Inspect" for details.

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Illustration 3	g01280419
Terminal locations at the P1 ECM connector (P1-22) Throttle input #1 (low) (P1-23) Throttle input #2 (low par) (P1-40) Throttle input #3 (high) (P1-41) Throttle input #4 (high par) (P1-29) Digital Return

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Illustration 4	g01250541
Terminal locations at the throttle switch (Terminal 1) Throttle input #1 (low) (Terminal 2) Digital return (Terminal 3) Throttle input #4 (high par) (Terminal 4) Throttle input #2 (low par) (Terminal 5) Return (Terminal 6) Throttle input #3 (high)

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and at the connector for the throttle switch.

4. Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and wiring for corrosion, for abrasion, and for pinch points from the throttle switch to the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Status of the Throttle Inputs

1. Connect the Cat ET to the service tool connector.

2. Restore the electrical power to the ECM.

Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

3. Observe the status of the throttle inputs on Cat ET while you operate the throttle switch in each position.
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   Table 1

   Throttle Input	Neutral	High "Rabbit"	Low "Tortoise"
   "#1 (Low)"	Off	Off	On
   "#2 (Low Par)"	On	Off	On
   "#3 (High)"	Off	On	Off
   "#4 (High Par)"	On	On	Off

Expected Result:

The status of the throttle switch corresponds with the table above.

Results:

• OK - 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.

  STOP

• Not OK - One or more of the inputs is incorrect. There is a problem in the circuit for the throttle switch. Proceed to Test Step 3.

Test Step 3. Check the Harness between the Throttle Switch and the ECM

1. Remove the electrical power from the ECM.

2. Fabricate a jumper wire that is long enough to create a short circuit across the connector for the throttle switch. Crimp spade terminals to each end of the jumper wire.

3. Disconnect the wires for the suspect throttle inputs from the throttle switch.

   1. Restore the electrical power to the ECM.

   2. Check the status of the suspect throttle inputs on Cat ET. Refer to Table 1.

   3. Use the jumper wire to short the wires for the suspect throttle inputs to the digital return wire at the switch.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

   4. Monitor the status of the suspect throttle input(s) on Cat ET.

4. Remove the jumper wire. Reconnect all wires to the original configuration.

Expected Result:

The status of the suspect throttle inputs change when the jumper wire is connected.

Results:

• OK - 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.

  STOP

• Not OK - The status of the suspect throttle inputs do not change when the jumper wire is installed. Proceed to Test Step 4.

Test Step 4. Check the Operation of the ECM

1. Remove the electrical power from the ECM.

2. Disconnect the J1/P1 ECM connector.

3. Remove the wires for the suspect throttle input(s) from the appropriate terminals at the P1 ECM connector.

4. Install a 208-0059 Adapter Cable As (70-Pin Breakout) at the J1/P1 ECM connector.

5. Connect the J1/P1 ECM connector.

6. Restore the electrical power to the ECM.

7. Check the status of the suspect throttle inputs on Cat ET.

   1. Use a jumper wire to short the terminals for the suspect throttle inputs to the digital return at the breakout T.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

   2. Monitor the status of the suspect throttle inputs on Cat ET.

8. Remove the jumper wire and breakout T. Reconnect all wires and connectors to the original configuration.

Expected Result:

The status of the suspect throttle input changes correctly when the jumper wire is connected.

Results:

• OK - The status of the suspect throttle inputs change 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.

  STOP

• Not OK - The status of the suspect throttle inputs do not change correctly.

  Repair: The ECM is not responding to the switch inputs. There is a problem with the ECM. Refer to Troubleshooting, "Replacing the ECM" before you replace the ECM.

  STOP