Section 5.1 MCM Wiring Harness

Section 5.1
MCM Wiring Harness

To determine if the MCM wire harness is causing starting difficulty, perform the following steps:‪

  1. Turn the ignition switch to the ON position.
  2. Install the Diagnostic Data Link (DDL) adaptor to the data cable and plug the adaptor into the DDL connector in the vehicle.
  3. Determine if MCM data is being received by the DDR. If no data is being received by the DDR, check for intermittent code or a fault and no codes by doing the following:
    1. Check for poor mating of the connector halves or terminals not fully seated in the connector body (backed out terminals).
    2. Look for improperly formed or damaged terminals. All connector terminals in the problem circuit should be carefully inspected to determine proper contact tension. Use a mating terminal to test the contact tension.
    3. Electrical system interference may be caused by a defective relay, or a switch causing an electrical surge. Look for problems with the charging system (alternator, etc.). In certain cases, the problem can be made to occur when the faulty component is operated as in the case of a relay.
    4. Verify alternator grounds are clean and making good contact. Disconnect the alternator belt to test.
    5. Wiggle wires and harnesses to try to make the problem active, or to occur again.
  4. If data is being received by the DDR, check the vehicle circuit breakers or fuses; refer to "5.1.1 Vehicle Circuit Breakers or Fuses Check" .

Section 5.1.1
Vehicle Circuit Breakers or Fuses Check

To determine if the vehicle circuit breakers are causing starting difficulty, visually check MCM circuit breakers or fuses to determine if circuit breaker(s) or fuse(s) are tripped or blown.‪

  1. If circuit breakers are tripped, determine cause and repair or replace as necessary; refer to OEM guidelines. Perform validation; "5.1.3.1 Test Engine with Repaired Power Harness"
  2. If circuit breakers are not tripped, measure the voltage at the MCM power harness. Refer to "5.1.2 MCM Unit Power Harness Voltage Test" .

Section 5.1.2
MCM Unit Power Harness Voltage Test

An Electronic Control Troubleshooting Guide is currently under development. Contact Detroit Diesel Customer Support Center at 313-592-5800 in the interim.‪

Section 5.1.3
Power Harness Repair

Perform the following steps to repair the power harness:‪

  1. Repair the damage to the power harness.
  2. Verify repair of the power harness; refer to "5.1.3.1 Test Engine with Repaired Power Harness" .
Section 5.1.3.1
Test Engine with Repaired Power Harness

To determine if the repair resolved the starter difficulty, perform the following steps:‪

warning

PERSONAL INJURY

To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.‪

  1. Attempt to start and run the engine, if the engine starts and runs, no further troubleshooting is required. Shut down the engine.
  2. If the engine fails to start and run, check for an empty fuel tank; refer to "5.2 Empty Fuel Tank" .


EPA07 MBE 900 DDEC VI Troubleshooting Guide - 6SE580
Generated on 10-13-2008

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