3126E On-highway Engine Caterpillar

Use this procedure under the following situation:

Use this procedure to determine if the Service Brake Pedal Position (Switch 2) is operating properly.

Service Brake Pedal Position (Switch 2)

The switch for the service brake pedal position (switch 2) is normally open when the respective pedal is released. Depressing the brake pedal should close the individual circuit. This switch is OEM supplied. The service brake pedal position (switch 2) is typically a pressure switch.

Illustration 1	g00770825
Circuit schematic for the service brake pedal position (switch 2)

Test Step 1. Inspect Electrical Connectors and Wiring

Illustration 2	g00770850
Pin locations for the ECM connector P2

1. Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector and the terminal 64 (service brake pedal position (switch 2)).

   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 switches.

   Refer to Illustration 2.

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 wiring for abrasion and pinch points from the sensor to the ECM.

Expected Result:

All connectors, pins and sockets should be 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: Perform the following 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 Service Brake Pedal Switch 2 on Caterpillar Electronic Technician (Cat ET)

1. Access the Cat ET status screen.

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

3. Start the engine. Ensure that the air system is charged if the vehicle is equipped with air brakes. Depress the service brake while the status of the service brake pedal position (switch 2) is being observed. Also, release the service brake while the status of the service brake pedal position (switch 2) is being observed.

   Refer to Table 1 for the status of the switch or for the status of the pedal position.

   Note: If the status indicates "Not Installed", check the programming of the "Transmission Style". This parameter must be programmed to "Automatic Option 2", "Automatic Option 3", "AT/MT/HT Option 2", or "AT/MT/HT Option 3".

Expected Result:

The switch status changes per the information in Table 1.

Results:

• Yes - The switch is operating normally.STOP

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

Test Step 3. Check the Switch Circuit

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 wires.

3. Disconnect vehicle harness connector P1 from the ECM.

4. Connect a breakout T to ECM connector J1 and connect P1 to the breakout T.

5. Install the jumper into terminal 64 (service brake pedal position switch 2) of the breakout T. Connect the other end of the jumper to ECM connector P1:52 (unswitched +battery) of the breakout T.

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

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

8. Access the Cat ET status screen.

9. While the status of the service brake pedal position (switch 2) is being monitored on the Cat ET status screen slowly remove the jumper from terminal 52 (unswitched +battery). Now, slowly insert the jumper into the terminal 52 (unswitched +battery).

   Refer to Table 2.

Expected Result:

The switch status changes per the information in Table 2.

Results:

• Yes - The ECM is functioning properly. 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 at the Service Brake Pedal Position (Switch 2)

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

2. Ensure that ECM vehicle harness connector J1/P1 is connected.

3. Find the switch for the service brake pedal position (switch 2) in the vehicle.

4. Disconnect the wires from the switch terminals.

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

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

7. Access the Cat ET status screen.

8. While the switch status is being monitored on the Cat ET status screen slowly connect the switch wires and slowly disconnect the switch wires.

   Refer to Table 3.

Expected Result:

The switch status changes per the information in Table 3.

Results:

• Yes -

  Repair: Perform the following repair:Replace the faulty switch.Verify that the repair eliminates the problem.

  STOP

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

Test Step 5. Insert a Jumper 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 wires.

3. Find the switch for the terminal for the service brake pedal position (switch 2). Also find the terminal for the sensor common for the +battery in the engine side of the bulkhead connector for the vehicle harness.

4. Insert the jumper wire between the two terminals in the engine side of the bulkhead connector.

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

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

7. Access the Cat ET status screen.

8. While the switch status is being monitored on the Cat ET status screen alternately remove the jumper wire between the two terminals, and alternately insert the jumper wire between the two terminals.

   Refer to Table 4.

Expected Result:

The switch status changes per the information in Table 4.

Results:

• Yes - The problem is in the vehicle wiring between the bulkhead connector and the switch.

  Repair: Perform the following repair:Inspect the vehicle wiring and repair the vehicle wiring, as required. If the problem still exists with the wiring, send the vehicle to the OEM dealer.

  STOP

• No - The problem is in the vehicle wiring between the bulkhead connector and the ECM.

  Repair: Perform the following repair:Inspect the vehicle wiring and repair the vehicle wiring, as required. If the problem still exists with the wiring, send the vehicle to the OEM dealer.

  STOP