This section should serve as a guideline for the technician:
- Intermittent Problems - Talk to the operator/driver. Be specific!
- Develop your own Driver Questionnaire. Refer to "6.2.1 Driver Questionnaire" .
Ask the driver to answer the following questions before attempting to repair an intermittent problem, or a problem with symptoms but no diagnostic codes. Use this and the response guideline to these questions.
- How often does the problem occur? Can you and the driver take the vehicle and demonstrate the problem in a short time?
- Has the vehicle been to other shops for the same problem? If so, what was done there?
- Did the radio, dash gages, or lights momentarily turn OFF when the problem occurred?
- Does the problem occur only at specific operating conditions? If so, at what load? Is it light, medium, or heavy?
- Does the problem occur at a specific engine operating temperature? If so, at what engine temperature?
- Does the problem occur only when above or below specific outside temperatures? In what temperature range?
- Does the problem occur during other conditions e.g. during or after rain, spray washing, snow?
- Did the problem occur at a specific vehicle speed? If so, at what vehicle speed?
- Does the problem occur at specific engine r/min? If so, at what engine r/min?
Questionnaire Response Guideline
The following are typical responses to the Driver Questionnaire:
- If the problem is repeatable, take the vehicle for a drive with the DDR connected and note the conditions when the problem occurs. Be prepared to take snapshot data using the DDR. Ensure you operate the vehicle after correcting the problem and duplicate the operating conditions before releasing the unit, to verify the problem is corrected.
- If the vehicle has been to other shops for the same problem, call the other shops and find out what has been done. Avoid replacing the same components again unless absolutely sure they are the problem! It is unlikely a component will fail again following a recent replacement.
- If other vehicle devices are affected, this indicates there may be something wrong with the ignition wiring. Refer to "91.2 Troubleshooting Vehicle Harness +5 Volt Supply" for information on inspecting the ECM battery connections.
- Operate the engine under similar load conditions. Check the fuel system for restrictions, primary filter, and fuel tanks for foreign objects blocking the fuel supply. Also, check the air system. Utilize the DDR snapshot feature.
- Operate the engine at this temperature while attempting to duplicate the problem. Use the snapshot feature on the DDR.
- If possible, troubleshoot the problem in this temperature range.
- If the problem seems to occur during or after the engine is subjected to rain/spray washing, thoroughly inspect the connectors for moisture entry.
- 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 DDR (snapshot) for changes to see if the pulse wheel (VSS signal) is loose.
- If the problem occurs at a specific engine r/min, unplug the oil, coolant, and air temperature sensors, and note any changes to the problem. Gather this data and contact Detroit Diesel Technical Service.
|DDEC III/IV Single ECM Troubleshooting Guide - 6SE497|
|Generated on 10-13-2008|