System Operation Description:
Use this procedure under the following situation:
Use this procedure in order to determine if the auxiliary brake circuit is operating properly.
The following background information is related to this procedure:
Auxiliary Brake Operation (Auxiliary Retarder) The auxiliary brake output circuit is provided by the ECM in order to indicate that conditions are acceptable for an auxiliary brake to operate.
Operation of the auxiliary brake output is inhibited during undesirable engine operating conditions. The time period of fueling the engine is an undesirable engine operating condition. The “Auxiliary Brake” parameter must be programmed to J1/P1:12 in order to enable the auxiliary brake output. The output will function on the corresponding output that is selected.
• ECM connector J1/P1:12
In typical applications, the auxiliary brake output circuit operates a relay, which switches battery power in order to energize the auxiliary brake solenoids. An “Engine Brake On” switch will be wired in series with the relay and the “Engine Brake On” switch must be ON before the auxiliary brake will operate.
The ECM does not read the OEM installed Auxiliary Brake Relay Switches in order to determine operation. Only the conditions that are listed below are used to determine operation. The OEM installed auxiliary brake relay switches determine the path of the signal.
In order to ensure the proper operation of the auxiliary brake, the following conditions must be met:
• Engine speed is above 800 rpm.
• The percent of accelerator pedal position is equal to 7 percent or the percent of accelerator pedal position is less than 7 percent.
• The clutch pedal is released.
These conditions must be met regardless of the following parameters:
• Customer Specified Settings for the Engine Retarder
• Auto Retarder in Cruise
• Engine Retarder Minimum Vehicle Speed
Additional operating requirements must be met if the “Cruise/Idle On/Off Switch” is in the ON position.
Cruise Control Switch in the ON position When the cruise control switch is in the ON position,
two special options allow the engine retarder to operate only after the driver depresses the service brake pedal. The customer programmable modes of operation are listed below:
• Coast mode
• Latch mode
• Manual mode
The Coast mode engages the engine retarder when the driver depresses the service brake pedal. The retarder disengages when the driver releases the service brake pedal.
The Latch mode engages the retarder when the driver depresses the service brake pedal. The retarder remains engaged until the control detects a change in a control input. Examples of a change in a control input are illustrated on the following list:
• Depressing the accelerator pedal
• Depressing the clutch pedal
• The engine speed drops below 800 rpm.
The third option for the “Engine Retarder Parameter” is Manual mode. In the Manual mode, the retarder operates in the same manner regardless of the position of the cruise control switch. Unlike the Latch mode and the Coast mode, depressing the service brake pedal is not required to initiate the retarder in the Manual mode.
Note: Latch mode and Coast mode determine engine retarder operation only when the cruise control switch is in the ON position. Latch mode and Coast mode do not determine engine retarder operation when the engine is active in cruise control.
Latch mode and Coast mode require the initiation of the service brake before acting. The initiation of the service brake disengages cruise control.
The “Auto Retarder in Cruise” parameter does not affect the operation of the auxiliary brake output circuit. The “Auto Retarder in Cruise” parameter is used only when the retarder is connected to the engine wiring harness.
Note: If the “PTO Configuration” is programmed to “Cab Switches”, “Remote Switches”, or “Remote Throttle”, the Auxiliary Brake Output is disabled whenever the PTO On/Off circuit is on. If the vehicle is equipped with an Anti-Lock Brake System (ABS), the vehicle may have an additional relay in the switch circuit for the auxiliary brake solenoids. This is installed so the ABS system can turn off the auxiliary brake solenoids, if necessary. The relay should have normally closed contacts.
The “Engine Retarder Minimum Vehicle Speed” parameter will prevent the operation of the auxiliary brake output below the programmed vehicle speed when vehicle speed is present.
The “Engine Retarder Minimum VSL Type” parameter provides the following two options:
• Hard Limit (default)
• Soft Limit
When the parameter is programmed to the hard limit, the “Engine Retarder Minimum VSL Type” does not allow the auxiliary brake to operate under the following condition:
• The vehicle speed is below the “Engine Retarder Minimum Vehicle Speed”. The “Engine Retarder Minimum Vehicle Speed” is customer programmed.
The soft limit also requires the vehicle speed to be equal to or greater than the programmed “Engine Retarder Minimum Vehicle Speed” in order to initiate the activation of the auxiliary brake, but the soft limit allows the operation of the auxiliary brake to continue below the programmed “Engine Retarder Minimum Vehicle Speed”.
The “Engine Retarder Delay” parameter provides a programmable delay after all of the basic conditions that are required to turn on the auxiliary brake are met. Once the conditions are met the ECM will delay the activation of the auxiliary brake by the programmed additional time. The programmable range is 0 to 3.0 seconds in 0.1 second increments.
Test Step 1. Inspect Electrical Connectors And Wiring
A. Thoroughly inspect ECM vehicle harness connector J1/P1, and the firewall bulkhead connector. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.
B. Perform a 45 N (10 lb) pull test on P1:12: Refer to Illustration 49.
C. Check the ECM Connector (Allen Head Screw) for the proper torque of 6.0 N·m (55 lb in).
D. 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 the wiring or replace the wiring, if necessary. Repair the connectors or replace the connectors, if necessary. Ensure that all of the seals are in the proper place. Ensure that all of the connectors are connected properly. Verify that the repair eliminates the problem. STOP.
Test Step 2. Ensure Correct Parameter Programming
A. Connect the Caterpillar Electronic Technician (ET) to the cab data link connector.
B. Turn the ignition key switch to the ON position.
C. Access the customer specified parameter screen in order to make sure that the ECM is programmed to use the auxiliary brake output.
D. Ensure that the auxiliary brake output is connected to the programmed output.
Expected Result:
The circuit is connected to the correct ECM terminal that is selected for the auxiliary brake output.
Results:
• OK – Proceed to Test Step 3.
• Not OK – Program the customer parameter to the correct terminal. STOP.
Test Step 3. Check the Parameter for “Engine Retarder Minimum Vehicle Speed”
A. Connect ET to the cab data link connector.
B. Turn the ignition key switch to the ON position.
C. Access the customer parameters screen in order to view the parameter for “Engine Retarder Minimum Vehicle Speed”. Refer to Troubleshooting, “Customer Specified Parameters”for additional information regarding “Engine Retarder Minimum Vehicle Speed”.
D. Ensure that the vehicle is not experiencing a problem due to this parameter.
Expected Result:
The problem is due to this parameter.
Results:
• OK – Explain the proper operation of the retarder and auxiliary retarder solenoids to driver. STOP.
• Not OK – Proceed to Test Step 4.
Test Step 4. Use ET to Check the Accelerator Pedal Position and the Clutch Switch
A. Connect ET to the cab data link connector.
B. Turn the ignition key switch to the ON position.
C. Use the following procedure to check the accelerator pedal position:
a. Access the status screen on ET for the accelerator pedal position.
b. While the status screen is being monitored, depress the accelerator pedal several times and release the accelerator pedal several times.
D. Use the following procedure to check the clutch pedal position switch:
a. Access the status screen on ET for the clutch pedal position switch.
b. While the status screen is being monitored, depress the clutch pedal several times and release the clutch pedal several times.
Expected Result:
The accelerator pedal position is between 3 and 100 percent, and the clutch pedal position switch indicates that the pedal is being depressed and released.
Note: The clutch pedal position switch is turned on when the clutch pedal is depressed. The clutch pedal position switch is turned off when the clutch pedal is released.
Results:
• OK – Proceed to Test Step 5.
• Not OK – There is a problem with the accelerator pedal position.
Repair: Perform the following diagnostic procedure:
Troubleshooting, “Accelerator Pedal (Throttle)
Position Sensor Circuit – Test”
STOP.
• Not OK – There is a problem with the clutch pedal position.
Repair: Perform the following diagnostic procedure:
Troubleshooting, “Clutch Pedal Position Switch Circuit – Test”
STOP.
Test Step 5. Use ET to Check the Relay and Solenoids
A. Turn the ignition key switch to the ON position.
B. Access the “Auxiliary Brake Special Test” on ET.
Access the following display screens in order:
• “Diagnostics”
• “Diagnostic Tests”
• “Auxiliary Brake Special Tests”
C. Turn the dash switches to the “High Braking Level” for the auxiliary brake. This is not the retarder solenoid switches that are connected to the ECM vehicle harness connector J1/P1:23 & 40.
D. While you listen for the relay and solenoids to click, cycle the “Auxiliary Brake Special Test” from the ON position to the OFF position back to the ON position.
Note: You may need to be near the engine in order to hear the click of the relay and solenoids.
Expected Result:
The relay and solenoids are operating.
Results:
• OK – The ECM is operating correctly. If the auxiliary brake or the relay is not operating, send the vehicle to the OEM dealer for repair. STOP.
• Not OK – Proceed to Test Step 6.
Test Step 6. Use ET to Check the ECM
A. Connect ET to the cab data link connector.
B. Turn the ignition key switch to the OFF position.
C. Disconnect the ECM vehicle harness connector J1/P1.
D. Connect a 70-Terminal Breakout T between ECM connectors J1 and P1.
E. Connect a voltage test lamp to terminal 65 (?Battery) and terminal 12 (Output 3) of the Breakout T.
F. Turn the ignition key switch to the ON position.
G. Access the “Auxiliary Brake Special Test” on ET.
H. While you monitor the voltage test lamp, cycle the “Special Test” from the ON position to the OFF position back to the ON position.
I. Stop the “Special Test”.
Note: A multimeter can not be used in place of the voltage test lamp when the ECM outputs are being tested.
Expected Result:
The voltage test lamp turns on when the test is active. The voltage test lamp turns off when the test is not active.
Results:
• OK – The ECM is operating correctly. The problem is in the vehicle wiring. 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.
• Not OK – Temporarily connect a test ECM. Use the “Auxiliary Brake Output Special Test” on ET to check the ECM. If the problem is resolved with the test ECM, install the suspect ECM. If the problem returns with the suspect ECM, replace the ECM. Verify that the repair eliminates the problem. STOP.
