3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Personality Modules that have a Software Date Code dated earlier than OCT01.

Use this procedure to determine if the fast idle lamp (P1:31 output 9) is operating properly.

Output 9 can operate as a fast idle lamp or a wait to start lamp. The "Output #9" parameter defaults to "Fast Idle Lamp" and the ECM will turn on output 9 when the fast idle is active.

Note: For "GM Truck Manufacturer" configurations, the "Output #9" parameter is unavailable and output 9 functions as an output only for the fast idle lamp.

Electrical Connections of the Lamp

One terminal of the lamp must be connected to battery voltage through the vehicle wiring. The other terminal is connected to the ECM at the vehicle harness connector P1:31.

The ECM provides a path to ground that will turn on the lamp.

Illustration 1	g00832955
Schematic for the fast idle enable switch

OCT01 Software

OCT01 and newer Personality Module Software also offers an alternative output that can be used for a fast idle lamp. The parameter "Output #9" is not used in the OCT01 software. The parameter "Fast Idle Lamp" has been added. "Fast Idle Lamp" can be programmed to "J1/P1:31" output 9, "J1/P1:21" output 8, or "None".

Illustration 2	g00834354
Schematic for the fast idle enable switch (OCT01 Option)

Test Step 1. Inspect Electrical Connectors and Wiring.

Illustration 3	g00834349
Location of Output 8 and Output 9

1. Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector, and the terminals for the fast idle lamp.

   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 lamp.

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 for 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: 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 for Normal Operation of the Fast Idle Lamp.

1. Verify that a fast idle enable switch is installed.

2. Connect ET.

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

4. Access the ET status screen. Verify that the following switches indicate the correct status:
   • The service brake switch 1 is off.

   • The service brake switch 2 is off.

   • The neutral switch is on.

   • The clutch switch is off.

   If any of the switches do not display the indicated status, fast idle will not activate.

5. Use the ET status screen to monitor the fast idle switch and the fast idle rpm.

6. Depress the fast idle switch while the status of the fast idle enable switch is being observed. Also observe the fast idle lamp. Release the fast idle switch. The fast idle lamp should turn on when the fast idle switch is pressed and released.

7. Depress the service brake pedal. The fast idle lamp should turn off when the service brake is applied.

Expected Result:

The switch status changes per the above information. The fast idle lamp turns on and the fast idle lamp turns off per the description above.

Results:

• Yes - The fast idle lamp is operating normally.STOP

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

Test Step 3. Test the Fast Idle Lamp Circuit.

Illustration 4	g00834351
Pin locations

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. Insert the jumper into P1:31.

   Note: For OCT01 and newer Personality Module Software, insert the jumper into P1:31 or P1:21. The terminal location depends on the programming of the "Fast Idle Lamp" parameter.

5. Connect the other end of the jumper wire to P1:65 (−battery).

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

7. While the lamp is being watched, insert the jumper wire and remove the jumper wire.

Expected Result:

Result 1 The fast idle lamp turns on while the jumper is connected to both sockets. Also, the fast idle lamp turns off when the jumper is removed from one of the sockets.

Result 2 The fast idle lamp does not turn on while the jumper is connected to both sockets.

Result 3 The fast idle lamp will stay on while the ECM vehicle harness connector is disconnected.

Results:

• Result 1 - The fast idle lamp is functioning properly. Proceed to Test Step 4.

• Result 2 - The fast idle lamp did not turn on. The vehicle's lamp circuit is not functioning properly. The lamp is probably burned out or there is a problem in the wiring from the cab to either the ECM or the +battery connection. Repair the lamp circuit or send the vehicle to the OEM dealer for repairs.STOP

• Result 3 -

  Repair: Perform the following diagnostic procedure:The circuit between the ECM and the lamp is shorted to chassis ground. Repair the circuit or send the vehicle to the OEM dealer for repairs.

  STOP

Test Step 4. Check ECM Operation of the Fast Idle Lamp.

Illustration 5	g00834353
Pin locations on the Breakout T

1. Disconnect ECM vehicle harness connector J1/P1.

2. Insert a breakout T between ECM vehicle harness connector J1 and ECM vehicle harness connector P1.

3. Connect one probe of the voltage test lamp to P1:65 (-battery). Connect the other probe of the voltage test lamp to P1:52 (unswitched +battery) of the breakout T.

4. The test lamp should turn on. If the test lamp does not turn on, either the test lamp is faulty or the wiring to the ECM is faulty. Continue with this step if the lamp turns on.

5. Leave the probe of the test lamp connected to P1:52 (unswitched +battery).

6. Connect the other probe of the test lamp to P1:31 (output 9) of the breakout T.

   Refer to Illustration 5.

7. Connect an ET. Access the following display screens in order:
   • Diagnostics

   • Diagnostic Test

   • Special Test

8. Activate the "Fast Idle Enabled Lamp" test. Observe the voltage test lamp. The lamp should turn on when the test is active. Also, the lamp should turn off when the test is inactive.

Expected Result:

The test lamp turns on and the test lamp turns off per the above description.

Results:

• Yes - The ECM is operating correctly. There is a problem in the vehicle wiring or the lamp.STOP

• No -

  Repair: Temporarily connect a test ECM. Check the ECM operation of the fast idle lamp when the test ECM is installed. If the problem is resolved with the test ECM, reconnect the suspect ECM. If the problem returns with the suspect ECM, replace the ECM.

  STOP