How to Diagnose By Symptoms

Since most of the fuel and emission control is electrically controlled, it is difficult to diagnose problems in the system. especially intermittent problems. Before undertaking actual checks, take a few minutes to talk with the customer who approaches with a driveability complaint. The customer is usually the best source of information on such problems, especially intermittent ones. By talking with the customer, one can find out what the symptoms are and under what conditions they occurred.

If a vehicle problem cannot be diagnosed using the Diagnostic Trouble Code section, it becomes necessary to troubleshoot the problem manually.

This section is divided into three major parts:

Symptom Identification Index: This index lists the most common emission system complaints, and provides a detailed description of each. Each listed complaint is assigned a symptom number.
Symptom Index

Quick-Look Diagnostic Chart: This chart identifies the relationship between the vanous components in the system and the assigned symptom numbers. It allows the user to quickly locate possible faults and to identify multiple symptoms having a common cause.
Quick Look Diagnostic Chart

Troubleshooting By Symptom: This portion contains diagnostic flow charts that show the procedures, inspection methods, and appropriate actions (repair/replace, etc.) necessary for fault isolation and removal.
Symptom Charts