Section 1.2 Operator Information

Section 1.2
Operator Information

This section should serve as a guideline for the technician. Talk to the operator/driver. Be specific!


Ask the driver to answer the following questions before attempting to repair an intermittent concern, or a concern with symptoms but no diagnostic codes. Use their responses to these general questions as a guideline:‪

  1. How often does the concern occur? (Can the driver operate the vehicle and demonstrate the concern to you in less than 30 minutes? If the concern is repeatable, take the vehicle for a drive with the Detroit Diesel Diagnostic Link (DDDL) connected. Start the snapshot at the beginning of the road test, use the mark user event space to track problems, and end the snapshot at the conclusion of the road test. Ensure you can operate the vehicle after correcting the concern without duplicating the symptoms at the operating conditions before releasing the unit to verify the concern is corrected.)
  2. Has the vehicle been to other shops for the same concern? (If so, call the other shops and find out what has been done. Avoid replacing the same components again unless absolutely sure they are the source of the concern. It is unlikely the same component will fail again following a recent replacement.)
  3. Did the radio, dash gages, or lights momentarily turn OFF when the concern occurred? (If other vehicle devices are affected, this indicates there may be something wrong with the ignition wiring.)
  4. Does the concern occur only at specific operating conditions? (Operate the engine under similar load conditions.)
  5. Does the concern occur at a specific engine operating temperature? (Operate the engine at this temperature while attempting to duplicate the concern. Use the snapshot feature on the DDDL.)
  6. Does the concern occur at a specific engine operating altitude? (If possible, troubleshoot the concern at this altitude.)
  7. Does the concern occur only when above or below specific outside temperatures? (If possible, troubleshoot the concern in this temperature range.)
  8. Does the concern occur during other conditions, e.g. during or after rain, spray washing, or snow? (If so, thoroughly inspect the connectors for moisture entry.)
  9. Did the concern occur at a specific vehicle speed? (If the problem occurs at a specific vehicle speed, check the parameters affecting vehicle speed to verify they are programmed close to the vehicle speed where the problem occurs. Check Vehicle Speed and watch the DDDL {snapshot} for changes to see if the pulse wheel [Vehicle Speed Sensor {VSS} signal] is loose.)
  10. Does the concern occur at a specific engine rpm? (If the concern occurs at a specific engine rpm, unplug the oil, coolant, and air temperature sensors, and note any changes to the concern. Gather this data and contact the Detroit Diesel Customer Support Center at 313-592-5800.)

MBE 900 and MBE 4000 EGR Technician's Manual - 7SE940
Generated on 10-13-2008

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