Usage:
Intermittent Problems
Intermittent electronic problems are extremely difficult to troubleshoot, especially when there is no diagnostic code logged. Recreating the intermittent problem is the first logical step. However, when the problem only happens once a week, it may take a week to recreate the fault. It is not cost effective to drive around for hours hoping the problem will reoccur. Randomly changing parts may fix the problem but usually results in future downtime for the truck. The purpose of this section is to provide step-by-step procedures which mechanics can use to troubleshoot intermittent problems without extensive road testing and random parts changing. Two types of intermittent failures are as follows:
Repeatable Intermittents - happen somewhat frequently (every 30 miles or several times an hour).
Unrepeatable Intermittents - do not happen frequently (every 500 miles or possibly once a week).
The mechanics time is best spent trying to recreate/isolate Repeatable Intermittents. However, trying to recreate/isolate an Unrepeatable Intermittent is not cost effective. Therefore, the first and most important step of isolating an intermittent problem is determining which type of intermittent it is. This should be done by questioning the driver and having he or she fill out the Driver Questionnaire which is supplied in this manual. Be sure to make copies of the questionnaire for future use. Finally, review the Test Status Checklist (if available) if the truck has been in a previous shop for the same repair.
P-101 Intermittent Engine Speed or Speed Burps
NOTE: The following procedure should only be used once the problem has definitely been determined to be Intermittent. Otherwise, refer to Section 2 of the 3406B Electronic Troubleshooting Guide, SENR3479, to isolate an Active problem.
Complete Steps 2 through 11
Each step will eliminate one subsystem (complete all steps).
Fill out a copy of the Unrepeatable Test Status Checklist at the back of this manual.
Return the truck to service with copies of both the Driver Questionnaire and the Unrepeatable Test Status Checklist.
Interview the driver once the truck returns.
If the problem is gone, work backwards using the "Diagnosis and Action When Truck Returns" column to determine which step has eliminated the problem.
