3126E On-highway Engine Caterpillar

Use this procedure under the following situation:

Use this procedure to determine if the fast idle switch is operating correctly.

The following background information is related to this procedure:

A fast idle switch (momentary switch) and a fast idle lamp can be installed. The operator can use the fast idle switch in either of the following ways:

• Press and release the fast idle switch in order to use the engine speed that is programmed into the "Fast Idle RPM #1" parameter.

• Use the accelerator pedal to accelerate the engine to the desired engine speed. Press and release the fast idle switch in order to maintain the engine speed at the desired engine speed.

A second programmable parameter "Fast Idle RPM #2" provides a second engine rpm set speed. The ECM will increase the engine speed from low idle to the engine speed that is programmed in the "Fast Idle RPM #1" parameter when the fast idle switch is pressed and then released. The ECM will set the engine speed to the rpm that is programmed in the "Fast Idle RPM #2" parameter when the fast idle switch is pressed and then released again.

Input 18 (terminal 40) is used as a switch input for fast idle operation. This feature does not require an input selection to be programmed to enable the switch input. A momentary connection between terminal 40 and a sensor common will initiate the fast idle operation. The "Fast Idle RPM #2" and/or "Fast Idle RPM #1" parameters must be programmed to the desired engine operating speeds.

The engine rpm set speed will not be maintained if any of the following actions occur:

• The service brake is depressed.

• The clutch pedal is depressed.

• The neutral switch indicates that the transmission is in gear.

A lamp can be connected to output 9 in order to indicate when fast idle is in operation. The "Fast Idle Enable Lamp" parameter must be programmed to "J1/P1:21" or "J1/P1:31" to enable the lamp operation.

Illustration 1	g00770407
Circuit schematic

Illustration 2	g00770414
Terminal locations for ECM connector P1

Test Step 1. Check the Electrical Connectors and the Wiring

1. Thoroughly inspect the ECM vehicle harness connector J1/P1, terminal 40, and the firewall bulkhead connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the fast idle switch circuit.

   The wires are on the following terminals:

   • J1/P1:40

   • J1/P1:5

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and the wiring for abrasion and pinch points from the battery to the ECM. Then, check from the ignition key switch to the ECM.

   Refer to Illustration 2 for terminal locations for the ECM.

Expected Result:

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

Results:

• OK - Proceed to Test Step 2.

• Not OK - Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.STOP

Test Step 2. Use Cat ET to Check the Status of the Fast Idle Switch

1. Connect Caterpillar Electronic Technician (Cat ET) to the cab data link connector.

2. Turn the ignition key switch to the ON position.

3. Operate the switch in the ON position and the OFF position.

4. View the "Fast Idle Switch" status on Cat ET.

   Note: A fast idle rpm must be programmed in order to automatically go to a set speed.

Expected Result:

The status screen should indicate "ON" if the switch is turned on. The status screen should indicate "OFF" if the switch is off.

Results:

• Yes - The switch is operating normally. Continue troubleshooting if the original condition is not resolved.STOP

• No - The ECM is not reading the change of the switch status. Proceed to Test Step 3.

Test Step 3. Check the Switch Circuit for the ECM

Illustration 3	g00770457
Terminal locations for the breakout T

1. Turn the ignition key switch to the OFF position.

2. Install a breakout T to the ECM vehicle harness connector J1/P1.

3. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to both ends of the wire.

4. Insert the jumper wire into terminal 40 of the breakout T. Connect the other end of the jumper wire to terminal 5 in the breakout T. Terminal 5 is AP sensor/switch common.

5. Connect Cat ET to the cab data link connector.

6. Turn the ignition key switch to the ON position.

7. Alternately remove the jumper wire and then insert the jumper wire from terminal 5. At the same time, monitor the status screen on Cat ET.

Expected Result:

The switch status changes to "ON" with the jumper wire in place. The switch status changes to "OFF" when the jumper wire is removed.

Results:

• Yes - The ECM is functioning properly at this time. Proceed to Test Step 4.

• No - The ECM is not functioning properly.

  Repair: Perform the following repair:

  1. Temporarily connect a test ECM.

  2. Remove all jumpers and replace all connectors.

  3. Recheck the system for active diagnostic codes.

  4. Repeat the test step.

  5. If the problem is resolved with the test ECM, reconnect the suspect ECM.

  6. If the problem returns with the suspect ECM, replace the ECM.

  7. Verify that the repair eliminates the problem.

  STOP

Test Step 4. Insert a Jumper Wire at the Switch

1. Turn the ignition key switch to the OFF position.

2. Reconnect the ECM vehicle harness connector J1/P1.

3. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to both ends of the wire.

4. Insert the jumper wire between the two switch terminals of the fast idle switch.

5. Turn the ignition key switch to the ON position.

6. Alternately remove the jumper wire and then insert the jumper wire at the switch terminals. At the same time, watch the status screen on Cat ET.

Expected Result:

The switch status changes to "ON" with the jumper wire in place. The switch status changes to "OFF" when the jumper wire is removed.

Results:

• Yes -

  Repair: Perform the following diagnostic procedure:Replace the fast idle switch.Verify that the repair eliminates the problem.

  STOP

• No - There is a problem in the wire harness between the fast idle switch and the ECM. Proceed to Test Step 5.

Test Step 5. Insert a Jumper Wire at the Bulkhead Connector

1. Turn the ignition key switch to the OFF position.

2. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to both ends of the wire.

3. Locate the socket for the fast idle switch in the engine side of the bulkhead connector for the wiring to the ECM.

4. Insert the wire jumper pin between the switch socket and the sensor common connection. Install the jumper wire on the engine side of the bulkhead connector for the wiring to the ECM.

5. Turn the ignition key switch to the ON position.

6. Alternately connect and then disconnect the jumper wire. At the same time, monitor the status screen on Cat ET.

Expected Result:

The switch status changes from "ON" with the jumper wire in place. The switch status changes to "OFF" when the jumper wire is removed.

Results:

• Yes - The problem is in the vehicle wiring between the bulkhead connector and the switch. Inspect the vehicle wiring and then repair the vehicle wiring. Otherwise, send the vehicle to the OEM dealer for repair. Verify that the original condition is resolved.STOP

• No - The problem is in the vehicle wiring between the bulkhead connector and the ECM. Inspect the vehicle wiring and then repair the vehicle wiring. Otherwise, send the vehicle to the OEM dealer for repair. Verify that the original condition is resolved. STOP