3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Use this procedure to determine if the neutral switch is preventing normal operation of cruise control, fast idle, idle set speed, or PTO operation:

The following switch circuits can also prevent the correct operation of the cruise control, fast idle, idle set speed or PTO operation:

• Service brake pedal position (switch 1)

• Service brake pedal position (switch 2)

• Neutral switch

• Cruise control set/resume switch

• Cruise control on/off switch

• PTO on/off switch

• cruise control pause switch

The switches are described in the respective circuit tests in Troubleshooting.

All of the following Customer Programmable Parameters can affect cruise control, fast idle, idle set speed, and PTO operation:

• "Low Cruise Control Speed Set Limit"

• "High Cruise Control Speed Set Limit"

• "Idle Vehicle Speed Limit"

• "Fast Idle RPM #1"

• "Fast Idle RPM #2"

• "Cruise/Idle/PTO Switch Configuration"

• "Idle/PTO Bump rpm"

• "Idle/PTO rpm Ramp Rate"

• "PTO Vehicle Speed Limit"

• "Cruise Pause Switch"

The vehicle speed calibration can also affect the Cruise Control, the Idle Set Speed, and the PTO if the vehicle speed calibration is incorrectly programmed. Refer to Troubleshooting, "Customer Specified Parameters".

Automatic Transmission Neutral Switch

The automatic transmission neutral switch is required when the "Transmission Style" parameter is programmed to "Automatic Option 3", "Automatic Option 4", "AT/MT/HT Option 3", or "AT/MT/HT Option 4". This switch is used to indicate when the automatic transmission is in neutral.

The automatic transmission neutral switch is an open circuit when the transmission is in gear. Shifting the transmission to the neutral position should close the circuit, which connects the input to the battery voltage. Many other switches in the system connect the input to ground when the circuit is closed.

This switch may not be connected to an input on the ECM. The parameter "Transmission Neutral Switch" determines the input to the ECM. If the parameter is programmed to J1/P1:62 a switch must be connected to terminal 62. If the parameter is programmed to "J1939", the switch position will be transmitted to the ECM over the J1939 data link. If a problem is suspected with the J1939 data link, refer to Troubleshooting, "Powertrain Data Link Circuit - Test".

The following background information is related to this procedure:

The kickout switch refers to the switch that is used to exit the cruise control, the fast idle, the PTO, or the idle set speed.

The operation of the Caterpillar electronic engine cruise control is similar to the operation of the cruise controls that are installed in automobiles. The operation of fast idle, idle, and PTO are similar to the operation of cruise except that the idle and the PTO govern engine rpm instead of vehicle speed.

Note: Idle in this procedure is an engine idle rpm above the programmed low idle rpm. Idle is set by using the cruise control on/off switch and the set/resume switch. Refer to Troubleshooting, "PTO Switch Circuit - Test" for additional information regarding the programmable options for the Dedicated PTO.

Note: Fast idle in this procedure is an engine idle rpm above the programmed low idle rpm. Fast idle is set by using a dedicated fast idle switch.

Cruise Control On/Off Switch

This switch must be ON before cruise control or controlled idle can be activated. This switch is ON when the switch is closed. When the switch is closed the following terminals are connected:

• ECM connector J1/P1 terminal 59 (cruise control on/off switch)

• Terminal 5 (AP sensor/switch sensor common)

Note: If the vehicle is programmed to use the "Dedicated PTO", the PTO on/off switch overrides the cruise control on/off switch. The PTO on/off switch overrides the cruise control on/off switch when the vehicle speed is within the range of the "PTO Vehicle Speed Limit" that is programmed.

Set/Resume Switch

With the cruise control on/off switch in the ON position and the vehicle speed within the range of the programmed "Low Cruise Control Speed Set Limit" and the "High Cruise Control Speed Set Limit", momentarily pressing the set switch will activate cruise control, and the ECM will maintain the current speed.

After a speed has been set and the speed is then disengaged by using the brake, the clutch, the cruise control pause switch, or the on/off switch, the ECM will seek the previous set speed when the resume switch is toggled. This assumes that the vehicle speed is above the "Low Cruise Control Speed Set Limit" for cruise control or the vehicle speed is below the "Idle/PTO Vehicle Speed Limit" for the idle and the PTO.

After a speed has been set, pressing and holding the set/resume switch in position will cause the engine to establish a new set speed. The system's reaction depends on the programming of the "Cruise/Idle/PTO Switch Configuration".

When the set/resume switch is momentarily pressed, the cruise set point will change one mph. The rate of change is dependent on the programmed "Idle/PTO Bump rpm" when the engine is setting on idle speed.

Cruise Control Pause Switch

The cruise control pause switch is not a switch that is wired to an input. The switch position is broadcast over a J1939 data link. The parameter "Cruise Pause Switch" must be programmed to use a cruise control pause switch. After a speed has been set and the speed is then disengaged by using the cruise control pause switch, the ECM will seek the previous set speed when the resume switch is toggled. This assumes that the vehicle speed is above the "Low Cruise Control Speed Set Limit" for cruise control or the vehicle speed is below the "Idle/PTO Vehicle Speed Limit" for the idle and the PTO.

Kickout Switches

The brake pedal position switches, the neutral switch, the cruise control pause switch, and the clutch pedal position switch are used in the cruise control mode, the PTO mode, the fast idle mode, and the idle mode to discontinue cruise operation, PTO operation, fast idle operation, or idle operation. The capability to override the idle shutdown timer is determined by the "Allow Idle Shutdown Override" parameter setting. The "Allow Idle Shutdown Override" is a Customer Parameter.

Usage of Transmission Style Switches

The "Transmission Style" parameter determines the switches that will be used. The following switches can be used with being dependent on the parameter setting:

• clutch pedal position

• neutral

• service brake pedal position (switch 1)

• service brake pedal position (switch 2)

Refer to Table 1 for additional information.

If the "Transmission Style" parameter is programmed to one of the following options, the input for the clutch pedal position switch is not used:

• "Automatic Options 1"

• "Automatic Option 2"

• "Automatic Option 3"

• "Automatic Option 4"

• "AT/MT/HT Option 1"

• "AT/MT/HT Option 2"

• "AT/MT/HT Option 3"

• "AT/MT/HT Option 4"

A Service Brake Pedal Position (Switch 1) is required for all configurations. The Service Brake Pedal Position (Switch 1) connects to the ECM through connector P1 terminal 45. The Service Brake Pedal Position (Switch 2) connects to the ECM through connector P1 terminal 64. The Clutch Pedal Position Switch connects to the ECM through connector P1 terminal 22. The neutral switch connects to the ECM through connector P1 terminal 62.

Some engines that were built before JULY 1999 may have a Basic ECM. The Basic ECM was used only on General Motors chassis. Other chassis used engines that were built with a Full Feature ECM. Basic ECM software does not have the parameter for "Transmission Style". For these systems, a jumper wire must be installed between the clutch switch input and the sensor common when an automatic transmission is installed. When the jumper wire is installed, the "Clutch Switch" status will always indicate "OFF". Engines that were built after JULY 1999 use only one type of ECM that can be configured for "Basic" or "Full Feature" operation. A new parameter was added in order to provide this flexibility. The "Truck Manufacturer" parameter was added in order to allow the configuration of the "GM Basic" operation or the "Other Full Feature" operation. This parameter is programmed at Caterpillar when the engine is built. The parameter for "Transmission Style" is not available for engines that have software that is dated prior to SEP00 and the parameter for "Truck Manufacturer" is programmed to "GM". SEP00 and newer engines that are programmed to "GM" use the "Transmission Style" parameter. The factory default for the "GM" setting is the "Universal" option. The "Universal" option provides identical features as the "Basic" system that is described above. If the "Transmission Style" parameter is programmed to the "Universal" option, a jumper wire must be installed between the clutch switch input and the sensor common when an automatic transmission is installed. Otherwise, the "Transmission Style" parameter can be programmed to match the specific arrangement of the vehicle.

If the problem is with undetermined Cruise/Idle/PTO kickouts use the following procedure:

Operate the vehicle in Cruise/Idle/PTO mode.

After the kickout, review the "ET Status" parameter. The "ET Kickout Status" parameter indicates the cause. This must be performed before the ignition key switch is turned OFF. It is important to remember that the parameter will only indicate the last kickout since the ECM has been powered by the ignition key switch.

The following Kickout Status parameters are available:

• "Cruise Kickout"

• "Idle Kickout"

• "PTO Kickout"

• "Fast Idle Kickout"

This parameter is blank when the ECM is first powered up. If this parameter is blank, "No Occurrence" is indicated. This parameter remains blank until the ECM detects the use of the Cruise/Idle/PTO Mode. Also, this parameter remains blank until the ECM detects the disengagement of the Cruise/Idle/PTO Mode. Refer to Tables 2, 3 and 4 in order to interpret the status screen kickout status parameter.

Illustration 1	g00646460
Schematic for transmission neutral switch

Test Step 1. Determine the Type of Problem.

1. Connect ET to the cab data link connector.

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

3. If the vehicle will not allow setting a Cruise speed, an Idle speed or a PTO speed, check the following Customer Parameters:

   Cruise Control Parameters

   • "Low Cruise Control Speed Set Limit"

   • "High Cruise Control Speed Set Limit"

   Idle Parameters

   • "Fast Idle RPM #1"

   • "Fast Idle RPM #2"

   • "Idle Vehicle Speed Limit"

   • "Idle RPM Limit"

   • "Top Engine Limit" (TEL)

   PTO Parameters

   • "PTO Configuration"

   • "PTO Vehicle Speed Limit"

4. Ensure that the vehicle is not experiencing a problem due to one of these parameters. Refer to Troubleshooting, "Customer Specified Parameters" for a description of the parameters, if necessary.

5. Check the status screen that indicates the last cause of a kickout for one of the following modes:
   • Cruise Kickout

   • Idle Kickout

   • Fast Idle Kickout

   • PTO Kickout

   Refer to Tables 2, 3, 4, and 5 for the meaning of the ET status screen parameter.

Expected Result:

The problem is due to a parameter setting or the problem is due to a normal kickout.

Results:

• Yes - Explain the proper operation of system to the driver.STOP

• No -

  Repair: Refer to Tables 2, 3, 4, and 5 for recommended troubleshooting.If a problem is still suspected with the neutral switch circuit perform the following procedure:

  Proceed to Test Step 2.

Test Step 2. Inspect Electrical Connectors and Wiring.

Illustration 2	g00705233

1. Thoroughly inspect ECM vehicle harness connector J1/P1, the firewall bulkhead connector and the terminals for the following switches in the connectors:
   • neutral switch (terminal 62)

   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 3.

• 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 3. Check Neutral Switch Status on ET.

1. Access the ET status screen.

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

3. Shift the transmission into the Neutral position while the status of the neutral switch is being observed. Also, shift out of Neutral while the status of the neutral switch is being observed.

Note: If the status indicates "Not Installed", check the programming of the "Transmission Style" Parameter. The "Transmission Style" must be programmed to "Automatic Option 3" or "Automatic Option 4".

Expected Result:

The switch status changes per the information in Table 6.

Results:

• Yes - The switch is operating normally.STOP

• Intermittent Problem Suspected - Proceed to Test Step 4.

• No - The ECM is not reading the switch status change. Proceed to Test Step 5.

Test Step 4. Operate the Vehicle and Check the Kickout Status Parameter.

1. For an intermittent Cruise Control Kickout, talk to the driver in order to determine the conditions when the kickout occurs. Topics of examination could be the following examples:
   • specific speed

   • road conditions

   • weather conditions

   Take the vehicle for a road test in order to duplicate these conditions and set the cruise control. Operate the vehicle in cruise control until the problem reoccurs.

2. For an intermittent Idle Kickout, talk to the driver in order to determine the conditions when the kickout occurs. A topic of examination could be the following example:
   • Specific engine rpm

   Start the engine. Duplicate these conditions and set the idle rpm. Operate the vehicle in idle until the problem reoccurs.

   Note: The status screen will only indicate the last kickout. The status screen will lose this information if the ignition key switch is turned OFF.

3. Connect ET and check the status screen for the last cause of the kickout. Refer to Tables 2, 3, 4, and 5 for an explanation of the status parameter.

4. If the status screen is blank, then either there was no kickout of the cruise control, or the power to the ECM was turned OFF before the information could be read. Repeat this test step.

   Note: A status screen that is blank indicates "No Occurrence".

Expected Result:

RESULT 1 The ET Kickout Status displays the following result:

• "Neutral"

RESULT 2 The ET Kickout Status displays the following result:

• "Switch Turned Off"

RESULT 3 The ET Kickout Status displays the following result:

• "Cruise Control PAUSE Switch"

RESULT 4 The ET Kickout Status displays the following result:

• "Brake"

RESULT 5 The ET Kickout Status displays the following result:

• "Vehicle Speed < Limit"

• "Bad Vehicle Speed"

• "Vehicle Speed ≥ Limit"

RESULT 6 The ET Kickout Status displays the following result:

• "PTO Switch ON"

RESULT 7 The ET Kickout Status displays the following result:

• "Clutch"

RESULT 8 The ET Kickout Status displays the following result:

• "No Engine Speed"

RESULT 9 The ET Kickout Status displays the following result:

• "Ser Switch Timeout"

• "Resume Switch Timeout"

Results:

• Result 1 - Proceed to Test Step 5.

• Result 2 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Cruise Control Switch Circuit - Test"

  STOP

• Result 3 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Powertrain Data Link Circuit - Test"

  STOP

• Result 4 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Service Brake Pedal Position (Switch 1) Circuit - Test"

  STOP

• Result 5 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Vehicle Speed Circuit - Test"

  STOP

• Result 6 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "PTO Switch Circuit - Test"

  STOP

• Result 7 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Clutch Pedal Position Switch Circuit - Test"

  STOP

• Result 8 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Engine Speed/Timing Circuit - Test"

  STOP

• Result 9 -

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Cruise Control Switch Circuit - Test".

  STOP

Test Step 5. Check the Switch Circuit for the ECM.

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 62 (neutral switch) of the breakout T. Connect the other end of the jumper to terminal 52 unswitched +battery of the breakout T.

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

7. Connect ET to the cab data link connector.

8. Access the status screen.

9. While the neutral switch status is being monitored on the status screen slowly remove the jumper from terminal 52 unswitched +battery. Now, slowly insert the jumper into terminal 52 unswitched +battery.

   Refer to Table 7.

Expected Result:

The switch status changes per the information in Table 7.

Results:

• Yes - The ECM is functioning properly. Proceed to test step 6.

• 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 6. Insert a Jumper at the Neutral Switch.

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

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

3. Find the neutral switch in the vehicle.

4. Disconnect the wires from the neutral switch terminals.

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

6. Connect ET to the cab data link connector.

7. Access the status screen.

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

   Refer to Table 8.

Expected Result:

The switch status changes per the information in Table 8.

Results:

• Yes - The switch is not functioning properly.

  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 7.

Test Step 7. 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 neutral switch terminal and the +battery connection 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 ET to the cab data link connector.

7. Access the status screen.

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

   Refer to Table 9.

Expected Result:

The switch status changes per the information in Table 9.

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