Symptom Analysis

PURPOSE OF THIS STEP
When an intermittent symptom occurs, get a full description of the symptom and the driving mode when it happens.

FINDING PROBABLE CAUSES
List sensors and actuators that could cause the symptom.

Refer to the Graphs and Charts and Diagnostic Reference Values.

Remember: Conditions and driving mode can provide clues to the cause of a symptom. For example, a hard start symptom with engine cold could indicate an Engine Coolant Temperature (ECT) sensor malfunction.

CHECK THE BASICS
Always make sure things like fluid levels, maintenance schedules, and proper vehicle use are okay. Old, clogged fuel filters can cause intermittent problems, as can low coolant levels and poor oil quality.

Good power and ground connections, and good harness condition are very important. Poor grounds and power connections (to injectors, for example) can cause intermittent symptoms.