Using Diagnostic Tables

Important: Understanding the table and using it correctly will reduce diagnosis time and prevent the unnecessary replacement of parts.

The Powertrain OBD System Check is an organized approach for identifying a problem. After the visual inspection is complete, the Powertrain OBD System Check should be performed. This Powertrain System Check will provide direction for diagnosis of the following:
^ A faulty or inoperative PCM
^ No serial data
^ Malfunction indicator lamp (MIL) inoperative
^ PCM DTCs.
^ Fuel system rich or lean
^ Customer Complaint Driveability Symptoms.
The Powertrain OBD System Check is designed as a Master table for driveability and emissions system diagnosis. The system check should always be used as the starting point for all engine control system diagnosis.


Diagnostic tables are an organized and systematic approach to diagnosing a Diagnostic Trouble Code (DTC). The table consists of five separate columns: step number, action, value, yes, and no. The step number indicates which step is being performed. The action column contains all necessary information about how to perform a certain test. The last sentence in each action block will always be a question. The question can only be answered yes or no. The answer to the question will dictate which column you will go to next - yes or no. The yes or no answer to each test will lead you to the next step to be performed or a particular action to take. Most boxes will have a Go to Step X statement. If a yes or no block does not have a Go to Step X statement, the text inside will be the last step taken on the table because it will either be a solution or a Fault not present condition.

Always begin with step 1 at the top of the table unless there is a notice or caution above it. Never skip steps or jump ahead in the table. Taking short cuts often leads to misdiagnosis. When a problem is found, make the necessary repairs and then verify the repair.