3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Use this procedure to determine if the circuit for the exhaust brake (output 3) is operating correctly.

The following background information is related to this procedure:

The exhaust brake relay circuit is provided by the ECM. The circuit indicates that conditions are acceptable for an exhaust brake to operate. Operation of the exhaust brake is inhibited during undesirable engine operating conditions.

When the cruise control on/off switch is in the OFF position, the following conditions exist:

All of the following conditions must be met in order to ensure the proper operation of the exhaust brake:

• Engine speed is above 1000 rpm.

• The accelerator pedal position is less than seven percent.

• The clutch pedal is released.

• The switch for the exhaust brake is on.

• The PTO on/off switch is off.

When the cruise control on/off switch is in the ON position, the following conditions exist:

"Exhaust Brake Mode" Parameter

When the cruise control on/off switch is on, this parameter provides two special options that allow the exhaust brake to be operated only after the driver has depressed the service brake pedal. The two modes of operation that follow are customer programmable:

• The "Coast" mode engages the exhaust brake when the driver depresses the service brake pedal. The exhaust brake disengages when the driver releases the service brake pedal.

• The "Latch" mode engages the exhaust brake when the driver depresses the service brake pedal. The exhaust brake remains engaged until the control detects a change in the control input. The following actions are examples of a change in a control input:

• The throttle is depressed.

• The clutch pedal is depressed.

• The engine speed drops below 900 rpm.

The third option for the Exhaust Brake Parameter is "Manual". The "Manual" mode operates in the same manner regardless of the position of the cruise control on/off switch. The driver is not required to depress the service brake pedal in order to initiate the exhaust brake. Depress the service brake pedal in order to initiate the exhaust brake in the "Latch" mode and the "Coast" mode.

Note: The "Latch" mode and the "Coast" mode are customer programmable options. The "Latch" mode and the "Coast" mode determine the operation of the exhaust brake only when the cruise control switch is in the ON position. The "Latch" mode and the "Coast" mode do not determine the operation of the exhaust brake when the engine is active in cruise control. "Latch" mode and "Coast" mode require the initiation of the service brake before acting. The action of the service brake disengages the cruise control.

Note: The output for the exhaust brake is disabled whenever the PTO on/off circuit is on and the customer parameter "PTO Configuration" is programmed to "Cab Switches", "Remote Switches", or "Remote Throttle".

Warm-up Mode

With OCT01 Software, the exhaust brake can be used to apply a parasitic load to the engine in order to aid engine warm-up. The exhaust brake will help the engine achieve normal operating temperatures. To use this feature, the parameter "Exhaust Brake Warm Up Configuration" must be programmed to "Warm Up Only" or "Exhaust Brake & Warm Up". Also, the on/off switch for the exhaust brake must be in the ON position and the parameter "Exhaust Brake Switch" must be programmed to "J1/P1:16" or one of the J1939 options. The "Warm Up Mode Idle Speed" parameter must be programmed to an engine speed between 700 rpm and 1400 rpm. If the preceding conditions are met, the engine will ramp up to the engine rpm that is programmed into the "Warm Up Mode Idle Speed" parameter.

Warm up mode will terminate when the engine reaches normal operating temperatures or when one of the following conditions are met:

• The service brake is depressed.

• The clutch pedal is depressed.

• The exhaust brake switch is turned off.

• The vehicle is in gear.

• The throttle is depressed.

• The vehicle speed is greater than one mph.

• The ECM detects an excessive load on the engine.

• The engine rpm is less than 500 rpm. The engine rpm is greater than 1450 rpm.

Exhaust Brake On/Off Switch

An on/off switch can be used to provide operator control of the exhaust brake in order to inhibit operation during undesirable conditions. Two different methods may be used. An in-line switch can be installed in the output circuit for the exhaust brake (terminal 12). The switch will turn the brake off by opening the circuit. This removes power from the brake relay. Opening the switch does not disable the output driver. Opening the switch disables the exhaust brakes.

With NOV99 and newer Personality Modules, an optional feature was added in order to provide an input to the ECM. The input is used to connect an on/off switch for the exhaust brake. The input uses terminal 16. When the switch is opened, the ECM will turn off the output circuit for the exhaust brake. This method allows the ECM to broadcast the correct status of the exhaust brake over the data link. With the first method that is described above, the brake can be disabled but the output remains active.

Note: If the on/off switch for the exhaust brake is installed in the output circuit, the "Exhaust Brake Switch" parameter must be programmed to "NOT INSTALLED". If the on/off switch is connected to the ECM switch input (terminal 16), the "Exhaust Brake Switch" parameter must be programmed to "INSTALLED".

OCT01 Software

Note: If the on/off switch for the exhaust brake is installed in the output circuit, the "Exhaust Brake Switch" parameter must be programmed to "NONE". If the on/off switch is connected to the ECM switch input (terminal 16), the "Exhaust Brake Switch" parameter must be programmed to "J1/P1:16". If the J1939 data link is used to transmit the status of the on/off switch for the exhaust brake, the "Exhaust Brake Switch" parameter must be programmed to "Cab Controller", "Body Controller", or "Instrument Cluster". If the parameter is programmed to one of the J1939 options, the switch status 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".

Illustration 1	g00729018
Schematic for the exhaust brake that is powered by a relay circuit

Illustration 2	g00837623
Schematic for the on/off switch that is connected to terminal 16

Illustration 3	g00837627
Schematic for the on/off switch that is connected in series with the output circuit

Illustration 4	g00729019
ECM terminal

Test Step 1. Inspect Electrical Connectors and Wiring.

1. Thoroughly inspect ECM connectors J1/P1 and the firewall bulkhead connector. 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 connections for the circuit for the exhaust brakes.

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 the 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. Connect ET and Check the Accelerator Pedal Position Sensor and the Clutch Pedal Position Switch.

1. Ensure that the cruise control on/off switch is OFF.

2. Connect ET at the cab data link connector.

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

4. Use the following procedure to check the accelerator pedal position sensor:

   1. Monitor the duty cycle of the throttle sensor on ET. Access the "Accelerator Pedal Position" display screen.

   2. While the duty cycle is being monitored on ET depress the accelerator pedal and release the accelerator pedal. Repeat this action several times.

5. If a manual transmission is installed, use the following procedure to check the status of the "Clutch Pedal Position Switch":

   1. Access the status screen onET for the "Clutch Pedal Position Switch".

   2. While the status screen is being monitored on ET, depress the clutch pedal and release the clutch pedal. Repeat this action several times.

Expected Result:

The duty cycle of the accelerator pedal position sensor is between 3 percent and 100 percent. The status of the "Clutch Pedal Position Switch" on ET changes from OFF to ON when the clutch pedal is depressed. The status of the "Clutch Pedal Position Switch" on ET changes from ON to OFF when the clutch pedal is released.

Results:

• OK - Proceed to Test Step 3.

• Not OK - Incorrect accelerator pedal position

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Accelerator Pedal (Throttle) Position Sensor Circuit - Test".

  STOP

• Not OK - Clutch switch status is incorrect.

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

  STOP

Test Step 3. Connect ET and Check the Solenoids and the Relays.

Illustration 5	g00769913
Breakout T

1. Connect ET at the cab data link connector.

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

3. Turn the switch ON for the exhaust brake.

4. Access the status screen on ET for the "Exhaust Brake Special Test".

5. Turn the on/off switch for the exhaust brake to the ON position.

6. Begin the "Exhaust Brake Special Test" while you listen for the solenoids to click. You may need to be closer to the engine in order to hear the click of the solenoid.

Expected Result:

All of the solenoids and all of the relays are operating.

Results:

• Yes - The ECM is operating correctly.STOP

• No - Proceed to Test Step 4.

Test Step 4. Use ET to Check the ECM.

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

2. Disconnect the ECM engine harness connector J1/P1.

3. Connect a breakout T to the ECM connector J1/P1.

4. Connect a voltage test lamp to terminal 12 (Output 3) and terminal 65 (-battery) of the 70-Terminal breakout T.

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

6. Access the special test for the "Exhaust Brake Special Test" on ET.

7. While the voltage test lamp is being observed, cycle the special test for the exhaust brake to the ON and OFF positions.

8. Stop the special test.

Expected Result:

The voltage test lamp behaves in the following manner:

• The voltage test lamp turns on when the test is active.

• The voltage test lamp turns off when the test is not active.

Results:

• Yes - There is a problem in the harness.

  Repair: Perform the following repair:Repair the engine harness or replace the engine harness. Verify that the repair eliminates the problem.

  STOP

• No - Verify that the switch for the exhaust brake is on and verify that the ET status screen reflects this condition. If the ECM is reading the switch status change, temporarily connect a test ECM. Repeat this test step. If the problem is resolved with the test ECM, reconnect the suspect ECM. If the problem returns with the suspect ECM, replace the ECM.

  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