793F CMD Off-Highway Truck/Tractor Braking System Caterpillar


MID 116 - CID 0168 - FMI 02

Usage:

793F CMD RBT
Conditions Which Generate This Code:


Illustration 1g02748103
Schematic of the system voltage circuit

This diagnostic code is associated with the system voltage of the machine that is supplied to the Brake ECM. The FMI 02 diagnostic code means that the Brake ECM has detected that the system voltage is erratic or intermittent. The Brake ECM activates this diagnostic code when the system voltage is not in the range of 18.0 VDC to 32.0 VDC. This condition must exist for more than a few seconds.

The possible causes of this diagnostic code are listed below:

  • A poor system connection of the ground circuit

  • A poor connection of the sensor voltage supply circuit

  • A charging system component has failed.

  • The Brake ECM has failed. This situation is unlikely.

Note: Before performing this procedure, verify that all circuit breakers and fuses in the charging circuit and the supply circuit of the ECM system are closed. If a problem with a circuit breaker or a fuse is found, correct the problem. Verify that this diagnostic code is active before performing this procedure.

Test Step 1. CHECK THE SYSTEM VOLTAGE OF THE ECM

  1. Turn the disconnect switch and the key start switch to the OFF position.

  2. At the J1 harness connector for the Brake ECM, insert a 7X-1710 Multimeter Probe along the contact of the system power J1-31 (wire 176-RD(Red)). Use the other multimeter probe to make contact to frame ground.

  3. Turn the disconnect switch to the ON position.

  4. Start the engine and run the engine at half throttle.

  5. Measure the voltage between contact J1-31 (wire 176-RD(Red)) and frame ground.

  6. Observe the resistance measurement of the multimeter and wiggle the machine harness connectors for the Brake ECM. Gently pull on the wires and move the wires around.

  7. At the J1 harness connector for the Brake ECM, insert the 7X-1710 Multimeter Probe that was used for the frame ground contact along the system power supply battery(-) contact J1-13 (wire A252-BK(Black)).

  8. Measure the voltage between contact J1-31 (wire 176-RD(Red)) and contact J1-13 (wire A252-BK(Black)).

  9. Observe the resistance measurement of the multimeter and wiggle the machine harness connectors for the Brake ECM. Gently pull on the wires and move the wires around.

Expected Result:

Both voltage measurements are approximately the same. Both measurements are in the range of 18.0 VDC to 32.0 VDC at all times during the manipulation of the harness and the connectors.

Results:

  • OK - Each voltage measurement is approximately the same. Each voltage measurement is in the range of 18.0 VDC to 32.0 VDC. The system voltage is correct at all times during the manipulation of the harness and connectors. Proceed to Test Step 6.

  • NOT OK - Each voltage measurement is approximately the same, however the measurements are not stable. The voltage measurements are showing a large amount of variation. The manipulation of the machine harness and connectors does not affect the measurement. Proceed to Test Step 4.

  • NOT OK - The measurement from the +battery contact to frame ground is stable and is in the range of 18.0 VDC to 32.0 VDC, however, the measurement between the ECM battery(+) contact and the ECM battery(-) contact is not stable in the correct range at all times. Proceed to Test Step 2.

Test Step 2. CHECK THE GROUND CIRCUITS

  1. Turn the key start switch and the disconnect switch to the OFF position.

  2. Disconnect the machine harness J1 connector from the Brake ECM.

  3. At the J1 harness connector for the ECM, measure the resistance between each of the four battery(-) contacts and frame ground. The contacts for the battery(-) connections are illustrated in the connection diagram at the beginning of this procedure.

Expected Result:

Each resistance measurement is less than 5.0 ohms.

Results:

  • OK - Each resistance measurement is less than 5.0 ohms. The ground circuit is correct. Reconnect the J1 machine harness connector to the ECM before proceeding to the next test step. Proceed to Test Step 3.

  • NOT OK - One or more of the resistance measurements is greater than 5.0 ohms. There is an open circuit or a poor connection in the ground circuit.

    Repair: The open or the possible poor connection is in the ground circuit for the ECM (wire A252-BK(Black)) in the machine harness. Refer to the complete Electrical System Schematic of the machine. Check the rear frame ground connection point where wire A252-BK(Black) is connected. Ensure that the ground connection is clean, that the ground connection is tight and that the ground connection is in good condition. Check all of the connectors and splice points that are in the ground circuit. Ensure that all connections are clean, that all connections are secure and that all connections are in good condition. Repair the machine harness or replace the machine harness.

    STOP

Test Step 3. CHECK THE SUPPLY CIRCUITS

The key start switch and the disconnect switch remain in the OFF position. The machine harness J1 connector remains disconnected from the ECM.

  1. At the J1 harness connector for the ECM, using a length of spare wire, measure the resistance between the alternator B terminal (wire 109-RD(Red)) to each of the +battery contacts that are connected to the J1 harness connector. The contacts for the +battery connections are illustrated in the connection diagram at the beginning of this procedure.

Expected Result:

Each resistance measurement is less than 5.0 ohms.

Results:

  • OK - Each resistance measurement is less than 5.0 ohms. The supply circuit is correct. Reconnect the J1 machine harness connector to the ECM before proceeding to the next test step. Proceed to Test Step 4.

  • NOT OK - One or more of the resistance measurements is greater than 5.0 ohms. There is an open circuit or a poor connection in the supply circuit.

    Repair: The open or the possible poor connection is in the ECM system voltage supply circuit (wire 176-RD(Red)) in the machine harness. Verify that there are no open circuit breakers or fuses in the circuit.

    Refer to the complete Electrical System Schematic of the machine. Check all of the connectors and splice points that are in the supply circuit. Ensure that all connections are clean, that all connections are secure and that all connections are in good condition. Repair the machine harness or replace the machine harness.

    STOP

Test Step 4. CHECK THE OUTPUT CURRENT OF THE ALTERNATOR

  1. Before performing this test step, partially discharge the batteries. Discharging the batteries can be done by cranking the engine for approximately 30 seconds without starting the engine. A discharge can also be done by turning on the lights without running the engine for about 10 minutes.

  2. Turn the disconnect switch and the key start switch to the OFF position.

  3. At the alternator, connect multimeter probes between the alternator "+" terminal (wire CBL-RD(Red)) and the alternator case (frame ground).

  4. Connect a clamp on an 8T-0900 AC/DC Clamp-on Ammeter or an equivalent ammeter around the output wire CBL-RD(Red).

  5. Turn the disconnect switch to the ON position.

  6. Start the engine.

  7. Run the engine at approximately half throttle.

  8. Immediately check the output current of the alternator.

Expected Result:

The output current of the alternator at half throttle is approximately 40 amps, half the alternator full current output rating (80 Amps). The current measurement is stable.

Results:

  • YES - The output current of the alternator at half throttle is approximately 40 amps and is stable. Proceed to Test Step 5.

  • NO - The output current of the alternator at half throttle is not stable. The measurement is showing a large variation of current values. The current output of the alternator is not correct.

    Repair: Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures for the alternator.

    STOP

Test Step 5. CHECK THE VOLTAGE OUTPUT OF THE ALTERNATOR

The multimeter and the ammeter are still connected from the last test step. The engine is running.

  1. Run the engine for approximately 10 minutes at half throttle.

  2. Check the voltage at the alternator output "B" terminal.

Expected Result:

The voltage measurement is 28.0 ± 1.0 VDC. There is little or no variation in the voltage measurement.

Results:

  • YES - The voltage measurement is 28.0 ± 1.0 VDC. The voltage is stable. The voltage output of the alternator is correct. Proceed to Test Step 6.

  • NO - The voltage is not stable. There is a large variation in the measured voltage. The voltage output is not correct.

    Repair: Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures for the alternator.

    STOP

Test Step 6. CHECK THE STATUS OF THE DIAGNOSTIC CODE

  1. Turn the disconnect switch and the key start switch to the OFF position.

  2. Reconnect any harness connectors that were disconnected and checked.

  3. Turn the disconnect switch and the key start switch to the ON position.

  4. Operate the machine.

  5. Determine if the CID 0168 FMI 02 diagnostic code is active.

Expected Result:

The CID 0168 FMI 02 diagnostic code is active.

Results:

  • YES - The CID 0168 FMI 02 diagnostic code is active.

    Repair: Perform this procedure again. Verify that the measurements of the alternator are correct. Verify that the circuit connections for the system voltage are in good condition. Verify that the connections are tight.

    If the problem remains and no cause can be found, the ECM may have failed.

    A failure of the Brake ECM is unlikely. Exit this procedure and perform this procedure again. Prior to replacing an ECM, always contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

    STOP

  • NO - The CID 0168 FMI 02 code is not active. The problem does not exist at this time.

    Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors. Resume normal machine operation.

    STOP

Caterpillar Information System:

2011/12/21 Improved Air Conditioning (AC) System in 793D Off-Highway Trucks {1802}
521B and 522B Track Feller Bunchers Machine Systems Piston Pump (Constant Horsepower Flow Control) - Test and Adjust
793F CMD Off-Highway Truck/Tractor Braking System MID 116 - CID 0041 - FMI 04
793F CMD Off-Highway Truck/Tractor Braking System MID 116 - CID 0041 - FMI 03
299D and 299D XHP Compact Track Loaders and 272D and 272D XHP Skid Steer Loaders Machine Systems Gear Pump
Improving the Air Conditioning System in 793D Off-Highway Trucks{1802} Improving the Air Conditioning System in 793D Off-Highway Trucks{1802}
521B and 522B Track Feller Bunchers Safety Messages
2012/01/31 A New Adapter Assembly Is Now Used In the Steering Column Group on Certain Off-Highway Trucks {4310}
966M XE and 972M XE Wheel Loaders Power Train, Steering, Braking, Hydraulic, and Machine Systems Output Transfer Gears
R3000H Load Haul Dump Cab Air Filter - Clean/Replace - If Equipped
R3000H Load Haul Dump Bucket Pivot Bearings - Lubricate
R3000H Load Haul Dump Braking System - Test
521B and 522B Track Feller Bunchers Machine Systems Pump Control (Output Flow) - Adjust
793F CMD Off-Highway Truck/Tractor Braking System MID 116 - CID 0168 - FMI 03
553C, 563C, and 573C Wheel Feller Bunchers TA2 Technical Inspection{1000, 7000, 753T} 553C, 563C, and 573C Wheel Feller Bunchers TA2 Technical Inspection{1000, 7000, 753T}
C27 and C32 Engines for Caterpillar Built Machines Housing (Front) - Remove and Install
793F CMD Off-Highway Truck/Tractor Braking System MID 116 - CID 0168 - FMI 04
521B and 522B Track Feller Bunchers Machine Systems Swing Motor Relief Valve Pressure - Test and Adjust
259D, 279D, 289D, 299D, 299D XHP, 299D2 and 299D2 XHP Compact Track Loaders, 257D, 277D, 287D, 297D, 297D XHP, 297D2 and 297D2 XHP Multi Terrain Loaders and 236D, 242D, 246D, 262D, 272D, 272D XHP, 272D2 and 272D2 XHP Skid Steer Loaders Piston Pump (Work Tool) - High Flow
2011/11/02 Coolant Additive is Now used on Certain Motor Graders {1352, 1395}
C27 and C32 Engines for Caterpillar Built Machines Housing (Rear) - Remove and Install
521B and 522B Track Feller Bunchers Daily Inspection
299D and 299D XHP Compact Track Loaders and 272D and 272D XHP Skid Steer Loaders Machine Electronic Control System General Information
773G and 775G OFF-Highway Trucks Engine Supplement Hood - Remove and Install
Back to top
The names Caterpillar, John Deere, JD, JCB, Hyundai or any other original equipment manufacturers are registered trademarks of the respective original equipment manufacturers. All names, descriptions, numbers and symbols are used for reference purposes only.
CH-Part.com is in no way associated with any of the manufacturers we have listed. All manufacturer's names and descriptions are for reference only.