Step 3: 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 the sensors and actuators that could cause the symptom.
- Refer to the EEC Graphs and Charts and the Diagnostic Reference Values in this section.
- REMEMBER: The conditions and driving mode can provide clues to the cause of the symptom.

Example: A hard start symptom with engine cold could indicate an Engine Coolant Temperature (ECT) sensor malfunction.

Check the Basics

- Always make sure of things like proper fluid levels, maintenance schedules, and vehicle use. Old, clogged fuel filters can cause intermittent problems, so can low coolant levels and poor oil quality.
- Good power and ground connections, and good harness condition are VERY important. Poor grounds and powers (to injectors, for example) can cause intermittent symptoms.